Advice on new telescope/accessories

[kkara4]

OK so bit of a noob when it comes to telescopes and have never owned one other than a Tasco 900mm 4 inch which my dad got as a birthday present back in the late 1980's!

Anyway feel the time is right to get one of my own now :)

I have done a fair bit of internet/forum trawling, so have come up with a list I think of what will be right for me, but looking to get advice from more knowledgable folk as to whether I am looking at the right things. There is a lot im not sure on, so ill start with what I know and then follow up with questions:


1) So in terms of use, I intend to never use an eyepiece and focus on using my Canon 5D MK III for photography or use the viewfinder/Live View for the viewing side of things.
2) I plan to get a scope around the 2000mm focal length mark. My thinking is that without an eyepiece that the magnification is purely a function of the focal length (could be wrong!) So 2000/50 = 40x magnification, which would mean something like the moon will fill the frame in the 5D viewfinder. I am judging this based on the 240-600mm lens I have at present which I use for all my astrophotography.
3) I plan to image primarily the moon and planets, and some of the smaller nebulae/DSO's.
4) I dont want anything rediculously heavy (<40Kg total would be nice).
5) Budget limit is $6K, but flexible.
6) High optical quality is essential, ie flat field, coma free as possible and aberration free as possible.

So based on these requirements, and looking at results that people have got , I am thinking the Celestron 925 HD is the right choice since:
-not too heavy
-not too expensive
-excellent image quality
-enough aperture to resolve detail on Jupiter/Saturn
-designed for use with DSLRs,
-2032mm focal length should be just right for imaging the moon
-Getting equilbrium temperature shouldnt take too long (<1.5 hours?) due to the vented tube (I am in Bellbowrie, Brisbane and the furthest I would go would be to Roma and that would be very rare, Wivenhoe dam would be much more common, but primarily backyard use. So I dont think dew/large temperature variations would be a big problem like they have in the USA or more colder/humid parts of AUS?)

along with a Televue powermate 5x and associated T ring/canon adapter since:
-general concensus is they are quality bits of gear they make
-not too expensive
-effective magnification (again not 100% sure if im right) would be 200x which should be generally useable in average-excellent seeing, and put a big enough image on the 5D sensor to get enough pixels on the target.
- I can always take it off when I want to image the moon.

After that, I kind of have no idea what else I need!

a) Due to the large magnification, I assume I will need some kind of motorised mount and tracking. Would Celestron's CPC GoTo mount be a good choice? I would like the whole tracking and alignment process to be as easy and smooth as possible.
b) I have heard that perhaps Celestron CGEM DX mount would be best since it is equatorial and motorised, but no idea what other equipment I would need in terms of tripod and scope mounting hardware?
c) Is the 9.25" aperture required to resolve good detail on Jupiter/Saturn? Would 8" be sufficient? I realise that the extra 1.25" would be welcomed for dimmer DSOs, and the approx 3.5kg difference in weight (telescope itself) isnt a big deal for me.
d) this could be a very silly question (so please forgive me) but is it possible to get a mount fast enough to track something like the ISS?
e) If neither of Celestron's mounts are a good choice, would it be worth getting just the optical tube assembly that they offer, and going to other companies for mounts/tripod?

Thanks in advance!

[astro744]

Note, focal length of C9.25 is 2350mm not 2032mm. That latter is for the C8.

A mount with an EQ platform would be better (dare I say essential) for astro-photography.

You can get a Meade LX80 8" OTA on HEQ5 mount for about $2.5k or a Meade LX600-ACF 10" f8 for about $7.3k. The latter has been designed for astro-photography and comes with many features especially for those imaging.

Both telescopes available from Bintel.

[kkara4]

Ah yes thanks for the pickup RE: focal length!

If the mount is fully computerised like the Celestron CPC, does that not track in the same manner that an EQ would? More for my understanding than suggesting id rather get fully computerised!

I will take a look at that Meade, for some reason I completely forgot about Meade's offerings!

[julianh72]

A computerized AltAz will tracks stars fine for visual use, but you will get "Field Roattaion" http://www.celestron.com/support/knowledgebase?article=http%3A%2F%2F www.celestron.com%2Fc3%2Fsupport3%2 Findex.php%3F_m%3Dknowledgebase%26_ a%3Dviewarticle%26kbarticleid%3D222 2%26group%3Diframe&title=What+is+field+rotation%3F+How +does+it+affect+my+scope%E2%80%99s+ viewing+and+imaging%3F which means that for long exposures, all stars will leave curved star trails around the centre of the image. For long exposures, you NEED an equatorial mount, and preferably with an auto-guider set-up attached.

[kkara4]

Thanks Julian. This makes sense now. What would the maximum exposure time realistically be for an altaz? I realise the answer to that probably depends on your magnification as well hmmm

[Amaranthus]

kkara, you can get away with about 25 sec exposures before field rotation starts to really bite and stars become too bloated from uncorrected random mount movement. I find 30 sec is pushing it a little too far and 15-20 sec is a bit underexposed.

Here are some examples of what I did on my alz-az mount with my 8SE.
http://www.astrobin.com/users/Amaranthus/

I doubt I'll be doing any more on this setup though, as I've now got my AZ-EQ6 mount up and running!

[kkara4]

Thanks Barry, those pictures are great! With your Saturn/Mars pictures I see you used a 2.5 Powermate, how is that enough magnification to get Saturn at such a good resolution? Or does the Neximage that you used have some kind of magnification associated with it?

[el_draco]

Just a few points, wont come close to answering all your questions but may help.

- The 9.25 inch HD is good scope and you have option of trying Hyperstar work at about F2 I wouldn't go 8". A bit small, C11 even better
- You'll also need to consider a starizona Microfoucser.
- Powermate 5X gives you a hell of of focal length and you miight like to consider the 2" 4x as an alternative. You can use it with 2 inch eyepieces as well.
- You can use the starizona cooling system to significantly reduce cool down time.

- Mount is going to be a balancing act. Long focal lengths require grunt and there a few alternatives.
a) dont know about CGEM's and don't know about the tracking of ISS
b) dont know about the build quality.
c) I owned and didn't like the EQ6 and I believe the EQ8 is problematic for some. Build quality may be an issue but I can't comment from experience. There are threads on IIS that talk about it.
d) I own a G11 G2. The build quality is beautiful but the operating system is a bit of a work in progress. They have been a workhorse for many people for many years for very good reasons, including flexibility and upgradability. Good news is they are pretty cheap at the moment and I think there are a couple in the classifieds. Bad news is they take some learning and you have to be prepared to do the learning. There are a lot of support resources available as well. I temporarily sold mine, then bought it back, which I guess says something. (Let the abuse begin ;))
The G11 is incredibly stable as well and will carry a lot of mass. It also separates in to a couple of easily managed units. The field tripod is a good option if you can get it.

- Undoubtedly, some will suggest an Astrophysics or TAK mount. I dont know much about either. Astrophysics makes good gear.

- C9.25 and G11 G2 are well within your budget and there are plenty of Losmandy plates for mounting everything

Overall, you are planning a good scope with a lot of potential to be a workhorse.

Man, you'll sure notice the difference over a 100 mm scope; wish I could be there when you see Saturn for the first time :eyepop:

Rom

[kkara4]

Many thanks for the reply Rom! I will look into using the 4x instead of the 5x, and agree I will need a rock solid platform to avoid vibrations and the like. Thanks for your opinions on the mounts, those Losmandy look pretty nice!

I just finished looking at the Meade's and that route is looking awefully expensive, while as you say the Celestron route comes in a bit cheaper.

I forgot to mention the scope is unusable at the moment, completely out of alignment after being shipped in a container from the UK when we moved here, and havent bothered aligning it!

Saturn comes up pretty good @ 600mm f/5.6 on my current unguided astro setup, but cant wait to make it a detailed view that doesnt have Saturn as a 25 ish pixels across size!

[Amaranthus]

kkara, you won't see planetary images like that visually - you need to use a planetary cam and take 1000s of frames, then stack the best ones. But visually, the C9.25 will still show really nice planetary views.

The NexImage 5 has a chip with a diagonal of 7mm, so on my f10 C8 the magnification was about 290x (or 720x at f/25)

[kkara4]

Thanks Barry, oh yes I assumed that you did a big stack, I use DSS for my widefield stuff and had a small play with Registax for some AVIs that I did but need a lot more practice I think! I guess what i meant to say was how great it looked in terms of the size in the image and the resolution you got it at, which makes perfect sense given you were magnifying at 290x effectively!

Since the 5D is a full frame sensor I need the powermates to boost up my effective focal length to get me an equivalent resolution image to perhaps what some of the CCDs can achieve...currently I get about 20 pixels across the rings edge to edge at 580mm = about 12x magnification. With the 2350 C9.25 and 4x powermate = 9400mm = about 188x magnification, I should get about 300 pixels across on Saturn. Just my initial calcs/thoughts!

[kkara4]

Rom is this the focuser you were referring to:
http://starizona.com/acb/Feathertouch-SCT-MicroFocuser---Celestron-Edge-HD-925CPC-925CGEM-925-P2994C654.aspx

And the cooler:
http://starizona.com/acb/Cool-Edge---SCT-Cooler---925-P3497C0.aspx

Both very reasonably priced (in the USA at least) i must say, I thought they would be a lot more expensive/lot more complicated!

[el_draco]

Yes. There are also replacement motorised vents for the HD scopes that vent air around the primary. You can leave them on all the time. If you get fancy, the microfocuser can be powered using a Starizona temperature compensation motororised setup. This connects directly to the microfocuser. You can also get dedicated focusers such as the Moonlight Crayfords to attach to the back of the scope. Pricey, but beautiful. You'll need to watch for the loss of backfocus if you go this way.

I have had a number of Celestron OTA's. All good; Meade has been hit and miss in the past. You may also consider a fast imaging Newtonian and there are lots to chose from Some amazing stuff I have seen from a few of them as well. G11 will cope with a 30cm F4 Maybe not as good for planetary though.

Rom

[kkara4]

Thanks Rom, I can see this hobby can spiral out of budget control pretty fast haha!

I have looked at the Newtonians but is IQ a fair bit lower than an Edge HD setup?

Also what would your suggestion be for the mount as opposed to the G11?

[el_draco]

Yes, well, we dont talk about budgets here. Some of us would have paid the mortgage out a LOT sooner but for astronomy... me included. :rolleyes:

IQ? I am assuming you mean image quality. Well, that'll cause a brawl for sure:rofl:

Its a matter of debate amongst amateurs that refractors are better than reflectors and SCT's because they dont have the central obstruction of a secondary mirror. But there is a lot more to it than that, including optics quality, aperture, seeing, mount, alignment, observer etc etc etc. You can look at a lot of images from different scopes and make up your own mind on that one. I have seen, recently, some shots through fast 8inch newts that make my jaw drop and images through big scopes that make you cringe. Many factors influence the result.

Most will say a TAK 150 is the ultimate bang for bucks in refractors but the competition aint far behind, and a lot cheaper! (TAK owners, I don't care and I am not telling you where I live :lol:) but from a beginners point of view, its not an issue; play with the top shelf stuff when you know you are in this for keeps.

I like the versatility of the HD's in terms of Hyperstar options F2, and long or medium focal length, (you can look that stuff up easily) They have a smaller visual FOV but lots of advantages including compactness. My C14 is about 1m long, (try doing that with a big refractor) and that has advantages for mounting.

I have built and used lots of scopes with the exception of an RC., ranging in size from 10"-29" (yes) newtonians; 2"-6" refractors and 8" to 14" SCT's. They all have their merits and image quality can vary dramatically in all of them. My first "big scope was a 12" F5 newtonian, and I loved it to death, (dropped the mirror:rofl:)

As far as mounts go, for your budget, and acknowledging that my knowledge of most mounts is limited, I would go G11 every time but there will be a range of opinions and some will vehemently disagree with me. History, however, looks favourably on the G11. Look in the equipment and reviews sections. See what others are using / saying. My last scope was C11 on a G11, G2 but I am currently "upsizing" and the dome is slowly rising. If you want to be mobile, I would not go bigger than this.

After decades of this hobby the one thing I have learned, and I still ignor it :D, is to keep it simple. This hobby will eat you alive if you let it. :lol:

[kkara4]

Thanks again for the reply Rom! Yes IQ was image quality, and I can understand the debate it will cause! I like all the images people have gotten with the C9.25 HD, that is one thing I did was to trawl around and look at what images I was happy with and the ones I wasnt. This was based on looking for basic things like coma, aberration, etc, and then sharpness. A lot of this has to do with the final CCD/camera choice I know, but I simply dont know enough people with scopes or have the time to go to star parties and things.

I really think I want to avoid a Newtonian, primarily due to the sheer size of it to meet my requirements. This will mean I will just look at it, and not ever use it. The same will happen if whatever I buy weighs as much as me. And that would be the worst buy ever since it would basically be a several thousand dollar display piece!

The G11 looks great, I think with the G2 version ill be blowing the budget though. I guess I have to decide on whether go to is really important or not to me. One feature I like is the ability to control the scope by ethernet/internet with the Gemini system though, that is awesome. I wonder if people on the other side of the world would be able to control it that would be pretty cool!

I havent looked into dedicated astrographs, I wonder if that is a route worth considering given that the camera will essentially be the eyepiece...hmm

[el_draco]

Yep, CCD does have a big impact on the final result. You'll also need to deal with the mono V colour issue. Many buy one shot colour and regret it because it precludes more complex imaging, Tri-colour, LRGB for example. Mono's more versitile in the end but you have to get a filter system at some point ... ah more $$.

You are correct in that newt's are physically bigger with issues around balance as well as size.



ah ha. Been looking at boxes for over a year. Very wise move




One of the biggest mistakes newbies make is under-rating the importance of a good mount. Spend a fortune on any OTA and whack it on something dodgy and you'll regret it terribly. Conversely, a good mount will make a less than ideal OTA better to use. I'd rather a 80mm refractor on a SB MX than a TAK 150 on an eq6. I finally entered the PME set last year. It meant I could not afford to set it up straight away but the payback will be in the fact that I wont need another mount, ever. :thumbsup:

Goto is not so important and until relatively recently, (20 years ago), goto was not available. We went "star hopping" However, tracking accuracy is paramount and a good G11 does that well. Yes, you can use it over the net, world wide.

A G11 at Bintel is about $5k but you can get them second hand cheaper:

http://www.iceinspace.com.au/forum/showthread.php?t=118101 (Good price @ $2800 if the tripod is with it) Same applies to the C9.25; they come up occassionally.

You might ask some questions of the owner or advertise in the wanted section for a G11. They come up surprisingly often.

[Camelopardalis]

Depending on your climate, a SCT may or may not be suitable. Down here in Sydney, I find that the corrector starts dewing around 85% humidity. So long as it stays around that it can be somewhat controlled with heaters, but at that point you're introducing additional local thermals that could affect your image quality.

I also have the Tempest fans fitted to my C11 Edge HD and they're great for equalising temperature gradients but have also found I need to watch the dew situation as they push so much air - and potentially moisture - thorough the tube, I've had it dew up on the inside a couple of times :sadeyes: I've just learned to use them sparingly. They are great though and don't introduce any discernible vibration into the image.

Take a look at the RC scopes such as http://www.bintel.com.au/Telescopes/Cassegrain/Bintel-GSO-RCA-200-f/8-Astrograph--Carbon-/602/productview.aspx they cost less at least in the smaller sizes than SCTs and have no corrector to dew up. I'm very happy with my Edge HD scope, but I'm mostly into visual...

Also, I'm no DSLR expert, but for planetary you might be better off with one of the faster frame rate CCD cameras, but a 5D should be nice for DSO imaging and at f/8 the RC-8 should give you a wide choice of the fainter targets to work on :)

Just a suggestion, but an RC-8 on AZ-EQ6 might be an interesting place to start, but the mount is everything as the focal length increases...

[kkara4]

Thanks for the reply Dunk. Those RCs look great, I will have to browse the specs/reviews on their 250 (10 inch) versions to see what they come with and what extra things I may need.

I really dont want to go towards CCDs, and instead try and utilise what I have to keep things simple and easy (and still potentially achieve great results). I think I will have to do some more reading on CCD vs DSLR imaging, because as I see it the 6.25 micron pixels on the 5D MK III should be able to get me good enough sampling on the planets provided the optical magnification is high enough. Basically need to understand for myself I guess why people use CCDs vs DSLRs. Later on down the line I suppose I can always go to a CCD if needed.

[Camelopardalis]

Absolutely..try it...the 5D III is quite a camera :thumbsup:

I use a little CMOS camera on my scope, magnification works out around 1000x (assuming my calculations are correct :D) based on C11 focal length along with a 2.5x powermate. This is my first season experimenting and it's a lot of fun :)

[raymo]

DSLRs used with skill and commitment, can get very close to the image quality of CCDs. I look at the best images from both, and wonder whether
the small difference is worth the extra cost,[ unless you are one of the world's finest imagers, and demand the absolute best]. If you really like
your 5D, I suggest you stick with it, for now at least.
raymo

[kkara4]

thanks Dunk and Raymo for the replies - I will stick to the 5D for now then and see what I end up with!

[kkara4]

Dunk, would this be the dew shield required if I did have a dewing problem?

http://starizona.com/acb/Astrozap-Aluminum-Dew-Shield---Celestron-925-Edge-HD-P3167C121.aspx

I think I would be naive to believe that I wont have a dewing problem, id rather consider it and be prepared for it than not. At the same time I dont want to make things too complicated!

I had a look at those GSO RCs, and then looked up some info on advantages and disadvantages of RC vs SCT for astrophotography. After reading this thread http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5836112/page/0/view/collapsed/sb/5/o/all/fpart/all/vc/1, I think I want to stick with SCT, I dont like the sound of collimating an RC constantly! It also sounds perhaps like the Edge HDs have maybe a slight advantage over the RCs, although I must admit I dont understand some parts of the discussion in that thread! (yet)

[The_Cat]

re: Undoubtedly, some will suggest an Astrophysics or TAK mount. I dont know much about either. Astrophysics makes good gear. "

In this day and age Electronics is very cheap but precision mechanics is always very expensive.

If you are looking at these mounts then the Takahashi mounts are better value for us in Australia. EM200 class is very good at c. $7000. The AP mounts are exceptional the smaller one is the mach1GTO BUT if you order one remember that every thing is an option so the price will be (in $us) very high and Customs will love you for importing one.

... Go on get one and help reduce the country's deficit !!

Clear skies,

Jeremy.

[kkara4]

Thanks Jeremy but I think I won't contribute to the defecit for the time being :P.

I will take a look at the mach1GTO though, but sounds way too expensive at this stage!

[Camelopardalis]

I use the Astrozap flexible dew shield (http://astrozap.com/Scripts/prodView.asp?idproduct=162) (for 11") as I find it squishes into a space in the car better :lol: I also have the heated version, although at some point I will get my hands on a separate heater tape as there is some evidence that heating the aluminium tube just behind the corrector is more effective at keeping it dew free than heating the thicker black (steel?) ring around the corrector. If you're serious about dew, check out the DewBuster (http://www.dewbuster.com/index.html) ;)

I've heard the RC can be a bit more interesting to collimate, but it also lacks a corrector. It's a difficult choice :D

As everyone has said, choose your mount carefully.

[kkara4]

Thanks Dunk, so it looks like there are heated and unheated dew shields then? Hopefully some other Brisbanites can provide some recommendations! Otherwise a heater sounds like an idea. Wont a heater though give you tube currents?

[Camelopardalis]

They're the same thing, pretty much - the heated shields just have the heater band in the (scope) end of the shield, that wraps around the thick metal around the corrector. The heater tape is more versatile IMO, in that you can vary the position more easily and find what is most effective for your scope/where you are.

Certainly, there's the risk of tube currents. It comes down to a bit of experimentation...if the heater is up too high, you can pretty easily see the heat haze, at least through an eyepiece.

[kkara4]

Thanks Dunk, I agree the tape version sounds better, I suppose there is a learning curve with all of these things and experimenting is the key!

[Camelopardalis]

Yeah, all part of the fun :D

[kkara4]

And as for the mount, looks like im about to pull the trigger on a G11 G2. I think it will be excellent for a C9.25 sized instrument (from all the replies so far and reading Ive done elsewhere) and all the accessories, and the weight will be manageable to boot. I like all the features and options for adding things in the future as well.

[Camelopardalis]

Very nice mate :)

Btw, just my opinion, but the Edge HD scopes are a nice visual scope - try it with an eyepiece sometime :lol:

[kkara4]

Thankfully it comes with one! As to how decent the included one is I havent looked into but I certainly plan to stick it in every now and then :P.

[Camelopardalis]

:lol: ah it'll be OK for a look now and then :D

[kkara4]

haha. OK so here is the shopping list:

Celestron 925 Edge HD OTA
Losmandy G11 G2 with tripod (trigger pulled)
Starizona cooler
Starizona feather touch microfocuser

And things im unsure of:

Televue PowerMate 2" 4x
Televue PTR-4201 T-Ring Adapter
Canon T-Ring adapter (from somewhere?)
Celestron dovetail adapter to mount to the G11 (needed?)
Dew Shield/heater TBD
12V power for mount?

Anything im missing?

Also has anyone bought from:
http://www.andrewscom.com.au/site-content-section-10-celestron.htm, and have any regrets?

[Camelopardalis]

What's the Starizona cooler you're looking at? If it's a gizmo that goes up the baffle tube you won't be able to use it since the Edge HD models have the corrector lenses lurking up there. For cooling your primary mirror area, I'd recommend the TEMP-est (http://www.deepspaceproducts.com/content/p/8/catid/4243) system.

Feathertouch micro focuser...not essential IMO...but check on the scope first whether it's got the large rubber focus knob (like the C11) or the smaller one (like the C8) as it's pretty straightforward to find focus with the bigger knob.

You'd probably benefit from a bahtinov mask or similar focusing aid - you can either make one yourself or buy one suitable for the scope.

Canon T-ring adapter shouldn't be hard to find, for example, BinTel one (http://www.bintel.com.au/Astrophotography/Camera-Adapters---T-Rings/Canon-EOS-T-Ring/36/productview.aspx)

You'll also need to interface the camera with the rear cell of the scope. The Edge HD 9.25" uses a 3.25" rear thread like the C11, so if it was just the camera, you could use something like the Celestron adapter (http://www.optcorp.com/ce-93646-t-adapter-for-9-25inch-11inch-14inch-edgehd.html), but I'm not sure how you'd interface the Powermate with it...the Celestron adapter has a male T-thread.

[Camelopardalis]

Btw, this is rolling of the tongue relatively easily because I recently decided to start doing some photography with my own Edge scope (with the guidance and teaching of best bunch of guys you could hope for :) ), so I'd not long back done all this reading around myself :thumbsup:

[kkara4]

Thanks Dunk! Always helps when someone is looking to go down a similar route!

The cooler I was looking at was
http://starizona.com/acb/Cool-Edge--...5-P3497C0.aspx

Although that may not be necessary if the Temp-est system is used?

I am just assuming that the powermate goes where the eyepiece would normally, but actually have no idea if that is correct or not, so thanks for your rear thread comment! I will have to look into this further.

[The_Cat]

Regarding:

"Canon T-ring adapter shouldn't be hard to find, for example, BinTel one "

Please note that if you intend to use a full frame size CCD be it EOS or any other you must consider a "Wide T" mount. Using a standard bayonet fitting on a standard T2 thread will show edge darkening , aka vignetting, of the image on these large CCD's.

Jeremy

[Camelopardalis]

Yeah it's still fresh in my mind, still experimenting but been getting some interesting results! Very exciting times :)

The Cool Edge basically goes in the hole opened up when you remove the Fastar secondary mirror. This is fine if you want to cool it down quickly at the start of a session, but you have to remove it and put the secondary mirror back in place before you can do any imaging ;) The Tempest system also do a secondary fan, same problem obviously. The more interesting ones are the Tempest fans that replace the side vents on the Edge HD tubes, as these are permanently mounted (it's only 2 little screws) and can be on while you're imaging, drawing a constant stream of air past the back of your mirror. As I've found out, just be careful if the air is moist and the temperature dropping as it'll draw moist air in there too and I've had my corrector mist up on the inside :sadeyes: maybe I should have just had the dew heater up higher :lol:

I'll be interested on what you find for the powermate... at the moment, I use a Clicklock visual back with Televue 2" to 1.25" adapter before the 2.5x powermate... but my little camera is only the size of a 1.25" plossl :D

[kkara4]

Ah thanks Jeremy! Televue do a wide T-ring adapter 2.4". I might have to get in touch with Televue to see what exactly I will need I think, that way no mistakes are made.

[kkara4]

haha yes the 5D is quite a big thing in comparison to yours! I will find out. I will look into the tempest system further, for some reason I thought the Cool Edge still allowed the use of the secondary (not sure why I thought that!). I can always turn the Tempest off as well if I find the tube currents get too strong/mist builds up! Will look into that further tonight!

[Camelopardalis]

Yeah the Tempest you can just pull the plug, or flick the switch if you put a switch inline :D

Down here in Sydney I don't find the temperature drops all that fast after the major post-sunset drop, which is when I have the fan running, but having the fans is better than not as you can somewhat control the temperature inside the tube...the fans move quite a volume of air!

[kkara4]

Sounds great Dunk thanks. I will do some breakfast reading up on the Televue stuff available as well as the Temp-est systems! So I would still need a heater with the Tempest system though wouldnt I, such as the dew shield that you use? Just making sure I understand it all!

[Camelopardalis]

Yeah you'll still need a dew heater tape AND controller, so you can vary the amount of heat/current through it.

So fans to cool the mirror at the back and heaters to keep the corrector at the front as clear as possible...nobody said it was a perfect system :lol:

[The_Cat]

Greetings,

Here are a couple of pics taken a few nights ago, please note the relative sizes of the moon and Saturn.

Interestingly the gear has similar base specs to what you are considering:

Telescope 254mm / F10 ... 2500mm focal length ... 2.5 m
Camera EOS 5D ... pixel size = 8.4 micro-metre ... 8.4e-06 m

Moon exposure ... 1/320 s
Saturn exposure ... 1/8 s

Moon occupies 1800 arc-sec diameter
Saturn largest at 20 arc sec max.

Image scale ... 8.4e-06 / 2.5

= 3.36e-06 radians per pixel

= 57.294 x 3600 x 3.36e-06 arc sec per pixel
= 0.69 arc sec per pixel

So, Saturn occupies 20.7 / 0.69 = 30 pixels
Moon occupies 1800/0.69 = 2597 pixels.

For a 9.4m focal length I would expect ( 9.4/2.5) x 30 pixels

ie. about 113 pixels. on the 5 D.

With pixels, say half size, one would expect Saturn to occupy about 230 pixels and this would make for a "respectable" size photo.

Clear Skies and kind regards,

Jeremy.

[kkara4]

Thanks Jeremy!

Your thoughts and calcs are inline with what I was predicting. I should note that the 5D MK III has 6.25 micron pixels (i know previously in my replies ive just stated "5D" and not the MK III part).

So on your rig if you have 5D MK III would be 2.5 rad/pixel = 0.516 arcsec/pixel. Then 20/0.516 = 39 pixels. Then 9.4/2.5 * 39 = 146 pixels.

using the powermate 5x would yield potentially 146*1.25 = 183 pixels on the disk of Saturn. I suppose trying it out will ultimately show me how happy I am with it. No choice but to go to an expensive CCD after that which I want to avoid doing if I possibly can.

I suppose there is a limit to the magnification madness, how steady mount is, how good seeing is, scope properly cooled and collimated etc.

ive yet to figure out how the powermate installs, but pretty sure now it goes in the Edge HD visual back like an eyepiece would.

[Camelopardalis]

The scope will come with a visual back, but I never used mine because it secures accessories with set screws and I replaced it with the Baader visual back (http://agenaastro.com/baader-2-sct-click-lock-eyepiece-adapter-visual-back-3-25-sct-thread.html) immediately. Astro Phyics also make a different one (http://www.astro-physics.com/index.htm?products/accessories/focus_adap/focus_adap). The Edge 9.25 has the 3.25" threaded cell like the 11 and 14, not the 2" one that the XLT 9.25 has.

The 5x powermate is only a 1.25" device, so you'd need a 2" to 1.25" adapter. Something sturdy. The last thing you want is something that has any play in it, as that can make all the difference when you're trying to get the object on the chip at high magnification! Not sure if it's worth considering, but the 4x powermate is a 2" device, so would clamp right into a 2" visual back. This should eliminate any vignetting from the 1.25" specs, although in reality if you're planetary imaging you probably don't care about that and would be capturing just at the centre of the chip anyhow.

Then you've got your TV powermate to T-adapter.

Another gizmo worth considering is a flip mirror...part of the fun I've had is getting the object (Mars) on the chip at high magnification (1000x)...it's on my wish list :D

Oh and collimation... Bob's Knobs :D the default screws are phillips type and precarious to adjust in the dark (I could only watch, with hands over my eyes :lol: )

[kkara4]

Dunk thanks for all the fantastic advice you have given!

I think you and the various articles around the place have sold me on the TEMP-est system. Think i'll go for the fastar option as well. :thumbsup:

I got a price of $3300 for the Edge 9.25 including insured freight, which is the best price ive been able to find so far. The sales director is extremely helpful and explained their tube checking processes which all made sense.

Good point about the 2" eyepieces, I forgot about the fact that the 5x powermate is a 1.25" device. Yes I will have to decide on whether the vignetting is important to me or not. I wonder how the 1.25 vs 2 inch size difference correlates to the percentage of the image vignetted on the sensor.

I also wonder if you can stack the 2x and 4x powermates together in 2" size. That would be 18800mm equivalent lol.

Looks like flip mirror for DSLR is unnecessary, because it pretty much has one in it already! Focus through viewfinder with Bahtinov Mask (or live view) then take picture!

[kkara4]

I also cant believe i havent heard of a Bahtinov mask before, and found an awesome generator online. Ive been struggling for years manually focusing my sigma lens on the Moon/Jupiter/Saturn :screwy:.

Just checked with my local acrylic cutter, going to get one laser cut out of black acrylic for the scope (when I get it to get accurate measurements) and for my Sigma lens too! $30 flat cost for laser cutting, A3 sheet for around $10. Not bad for 2 masks.:thumbsup:

[Camelopardalis]

Yeah you're right about the flip mirror - sorry! Must refrain from posting before the coffee is working :lol:

Bahtinov masks are pretty awesome, although on my DSLR I don't find it all that hard to get nice little discs of stars...the mask removes the element of ambiguity, and that appeals to the OCD side of me :D

[el_draco]

I've used the Baader Visual back on a C11. FABULOUS bit of kit. Will hold anything like a vice.

[kkara4]

Thanks Rom/Dunk, Baader Visual Back (3.25 to 2") is added to the shopping list. Might be able to get it from the same store as the OTA, will find out tomorrow!

Just to confirm it is this part?
http://agenaastro.com/baader-2-sct-click-lock-eyepiece-adapter-visual-back-3-25-sct-thread.html

So i think the way to do it is --Baader Visual Back -- Powermate 4x 2" -- Wide T ring adapter -- Canon T ring.

if i want to go visual, simply eye piece straight into the Baader.

if I want to go prime length, --Baader Visual Back -- 2" to Wide T ring adapter -- Canon T ring.

Hmm just need to find the wide t ring adapter and 2" to wide T ring adapter now.

The Televue 31mm Nagler looks like such a nice eyepiece but so much $$$! Perhaps Ill leave that out for the time being

[Camelopardalis]

Yeah that's the right visual back :thumbsup:

If you try any visual you'll also want to use a diagonal, but iirc Celestron include one in the box.

For prime (f/10) you might want to consider the Celestron T-adapter for Edge HD as it gets the backfocus right when using a Canon :) You basically remove the visual back and it screws on the rear thread, presenting a male T-thread, see here http://www.optcorp.com/ce-93646-t-adapter-for-9-25inch-11inch-14inch-edgehd.html

Regarding the Nagler...beautiful piece of kit, but if you'd only be visual occasionally the ES 82 30mm is practically as good at f/10 and a fraction of the price.

[astro744]

I think you need the Tele Vue PTR-4201 4x Powermate T-ring. See http://www.televue.com/engine/TV3b_page.asp?id=123&Tab=_acc#.U5bXs9oaySM

See also http://www.televue.com/engine/TV3b_page.asp?id=123&Tab=_con#.U5bZetoaySM

The top of the Powermate unscrews and the PTR-4201 screws on instead. The standard camera T-ring screws onto the PTR-4201.

There is a version for the 2x Powermate as we'll as one that is suitable for both 2.5x and 5x Powermates. These adapters allow the Powermates to be used for imaging as designed without vignetting and at the correct magnification.

[kkara4]

ahh many thanks for the reply, I see now. And since the T adapter is for the 2" size it should inherently be a "wide" version! Then all I need is the canon T-ring from somewhere.

would I be correct in saying:

1) if i wanted to do prime focus id have to take out the Powermate, and get a separate Wide T ring to 2" adapter?
2) if I wanted to go back to normal visual, just remove the powermate and insert eyepiece straight into Baader visual back?

[astro744]

1) Yes. Prime focus = T2 adapter + camera specific T-ring
2) Yes, but you may need extension tube to reach focus or a better solution is to use star diagonal for visual which also gives a more comfortable viewing angle.

[The_Cat]

Sorry about the late reply just attended a meeting of the " Solar Citizens".

My camera is the EOS 5D Mk 1 ... The old one! and the scope is a Takahashi Mewlon 250CR ... A corrected version of the original Mewlon.

These calcs are correct if not simple as they say nothing about the optics or seeing etc. the main thing to note is the dimensions I've put ar the end of the lines.

I'm sure there is a limit to magnifying an image a big problem is the mount and its stability. With a focal length of 4.9 m it is a real problem keeping things steady. If the wind blows or one walks near the rig one will see movement. seeing will cause a major problem especially as the diameter increases. But for planetary ( put out a call to Mr Paul H.) for all the fine points on this specialised field.



The main thing about all this stuff is to "Do It" and you will get better and better. don't bother with overly expensive stuff ... Some of the niceest images I've taken were with an EOS 350D. if you like I can post a couple for you ... Remember the camera was an EOS 350D.


Jeremy.

[kkara4]

Thanks for the reply. Is a T2 adapter the notation typically used for a wide T adapter as opposed to a normal one? Just trying to understand the jargon!

EdgeHD 9.25 comes with a 2" star diagonal which slips into the 2" visual back and accepts a 2" eyepiece so all good there then!

[kkara4]

Thanks Jeremy.

I have the MK I as well, and love the MK III in comparison that's for sure! Since I already have the MK III thought I might as well put it to use on the telescope, hopefully I manage to get some good pictures.

I think the Losmandy G11 (with upgrades) should perform well for me.

Now something I havent thought of is the guiding, but I will talk to the G11 seller to see what is included on that front.

[astro744]

No, T2 does not refer to wide version. See history of 'T' mount at http://en.wikipedia.org/wiki/T-mount

I cannot remember who sells the wide body T2 adapter. If the barrel of the adapter is 2" then the only other restriction is inside the adapter and the T-ring. You may be able to get a special SCT wide T2 adapter from Baader that is larger than 2". I'm not familiar with what is available here.

[kkara4]

thanks, I will take a look at that article and have a read! I got an email back from Televue from John Rhodes, managed to dig up his email address from google. He has been most helpful, but will fire back a few questions to confirm a few things, then should be able to complete the shopping list :)

[Camelopardalis]

OK, so I was curious about this so here's what I've found so far...

I measured my T-adapter for EOS...the clear aperture is 42mm...which coincidentally appears a lot in Celestron's white paper for Edge HD :D

Then I did some basic calculations... the 5D Mk III has a chip size of 36x24mm, which gives a diagonal of 43.26mm. So from that, I'd guess you might see a little vignetting in the corners :confused2:

It might be a little worse than that because any scope->T or powermate->T has to have some additional incursion into that diameter, even if it's thinly constructed. I'm no optical path expert but from my basic understanding you might see some vignetting when you try to utilise the absolute full frame, but it'd be interesting to see by how much.

[astro744]

I found this one with a 47.5mm clear aperture and integral Canon EOS T-ring.

http://www.bluefireball.com/product-p/p-11.htm

Note this will be good for prime focus alone but you will need a separate Canon EOS T-ring to screw onto the Powermate T-ring adaptor when using Powermates.

Available at http://agenaastro.com/parts-accessories/adapters/camera-adapters.html?manufacturer=87 but currently out of stock of EOS model.

[mithrandir]

http://www.telescopeadapters.com/ have a one-piece T-ring and 2" tube for Canon. 2" UltraWide Prime Focus Telescope Adapter They don't vignette like the ring and tube ones do. I have them for my Sony cameras and find the no-undercut version works better on my scopes.

[astro744]

Thanks. That's the website I had in the back of my mind but couldn't find it and then found the Blue Fireball site which has a similar one piece T-adapter.

[kkara4]

Thanks a lot for the replies guys. When I get some time tonight ill have a look at all the options/links you have all provided!

[kkara4]

ok so something that is still confusing me is what exactly I will need for the guiding part. As I understand it, guiding with high precision is required for high magnification imaging? Can this be done relatively inexpensively? If so what components do I need?

The G11 I have bought has been tested to have periodic error less than +/- 2 arcsec, but as I understand it guiding must be used so as to minimise the periodic error and drive it to near-zero.

Also with polar scopes, does that alignment also have to be done extremely precisely? I believe the G11 comes with a polar scope but not sure at this stage how good it is or if it will suit my intended imaging targets

[Amaranthus]

Polar scopes and software algorithms are great for EQ visual, but only get you so-so close. In the end, for AP, you must drift align. The most efficient way to do this, IMHO, is the DARV method or variants thereof.
http://www.cloudynights.com/item.php?item_id=2838

[astro744]

The more accurately you align the less you will have to correct when guiding. Use the drift alignment method for polar aligning. You will get field rotation if you are doing long exposures and are correcting often due to poor polar alignment.

[kkara4]

Thanks for the reply Barry.

the DARV method seems to be ideally suited to what I am doing since I am mostly going to be using a DSLR!

But just to clarify, is this DARV method to achieve correct polar alignment as opposed to contrinuous guiding? I have some more questions about the DARV method linked though, am confused by a few steps and what happens between some of the steps!

[kkara4]

Thanks for the reply!

This makes sense, but isnt guiding still required because the periodic error must be near zero for high magnification photography?

Like even with 1 arcsecond period the image would still drift around enough to cause the image to be blurry if I took say a 2 minute video of Saturn at 200x power wouldnt it?

[Amaranthus]

Accurate Polar alignment + AG are definitely required for long-exposure AP.

D.A.R.V. type corrections + PEC are sufficient for 1-2 min unguided, maybe more for your G11 which is a quality mount.

[Amaranthus]

Here is a short summary, modified from another helpful post on IIS that I struggled to re-locate!

1. Point telescope east roughly 30 deg above horizon.

2. Start the webcam/CCD/DSLR with a 45 sec exposure

3. Wait 5 secs, at guiding speed, move mount using RA controls for ~20 secs, then reverse direction for the remaining 20 secs (no pause)

4, The image will show a star trail in a "V" pattern. The gap is how far out your Polar Alignment is.

5. Adjust your Alt manual adjustment a little. Then repeat the above exp/move again.

6. If you have adjusted the mount in the right direction the gap in the "V" should have gotten smaller, if bigger you've adjusted the mount in the wrong direction. Make appropriate adjustments again.

7. Continue until you get a straight line.

8. Then slew to about DEC zero (celestial equator) and near the Meridian, and repeat but this time adjust the azimuth and repeat until line is straight.

Go longer exposure for a better PA. The reason for the 5 sec pause means you can tell which line is which as on will have a blob at the start.

[astro744]

Precise polar aligning eliminates north or south drift (DEC axis).

Guiding corrections east or west may be needed to counteract slow/fast movements in RA drive. PEC should typically correct this depending on how good it is.

Note if you align so that there is no drift in DEC for say 10 minutes then you can photograph for 10 minutes without an issue. The PEC function of the drive should correct in RA axis. You don't have to align so accurately that you don't get drift for say 30 minutes if you don't intend on taking single exposures 30 minutes long.

[kkara4]

Thanks Barry, what does PEC stand for?

[kkara4]

thanks guys starting to make sense, and Barry that makes much more sense with the DARV procedure now! I still fail to see though how one would slew to true 0 declination without being in the middle of the ocean so you have a proper 0 horizon? and then do you find a star just as it comes above the horizon?

[Amaranthus]

DEC zero, not ALT zero :) At my horizon, this is about 55 degrees altitude at the Meridan. Look up "Celestial Equator" for the theory.

PEC = Periodic Error Correction - corrects systematic anomalies in your worm drive, after a few cycles of training.

[kkara4]

Ahhh thanks Barry, my bad! All makes perfect sense now. So DARV gets you pretty much perfect polar alignment, then only the periodic error which must be dealt with, either with PEC or true autoguiding.

That is awesome, means I wont have to worry about a polar scope at all, even if one ends up coming with the G11.

Now if I did want to do long exposure (lets say 30 minutes +), what would I need for the guiding side of things in terms of equipment?

[Amaranthus]

You can do PEC + AG if you use pulse guiding. Then AG is only correcting for the stochasticity, leaving PEC to deal with the determinism ;)

If you are working at a long FL you'll ideally want an off-axis guide port and sensitive CCD guidecam. If shorter FL (widefield), then a guidescope and CMOS guidecam are fine (this is what I currently use, even for my C8 @f/6.3)

[kkara4]

Thanks Barry. What would I need exactly for the AG part in your first paragraph?

For your second paragraph, what do you use for the guidescope and guidecam?

[Amaranthus]

A sensitive guider that uses a CCD for an OAG setup. Lodestar or similar.

I use a NexImage 5 planetary cam or Orion SS G3 as my guider (the latter is my basic mono CDD imager, I use it as a good AG when imaging with my DSLR). Guidescope is either my ED80T CF (when imaging with the C8), or my SW120 achro (when imaging with the ED80T). But most people go for a dedicated 80 mm achro guidescope.

[kkara4]

Thanks Barry

I think What I will do is stick to un guided at first, purely from a cost perspective, and if I find I end up desiring an autoguided setup I can always invest in a dedicated guidescope then :). Because sounds like we are talking $2K plus to autoguide, way blowing the budget (which ive already blown lol).

I think with 1 minute of unguided accuracy I should be fine, and I dont think planets will be an issue because frames which drift could simply be discarded anyway.

[Amaranthus]

Not necessarily You can get a basic but robust AG package for under $600:
http://www.bintel.com.au/Astrophotography/Autoguiders/Orion-Awesome-Autoguider-Package/404/productview.aspx

[kkara4]

Thanks Barry that looks awesome! i thought i was pretty much looking at a proper 80mm refractor and all the trimmings to get a decent guiding setup!

[kkara4]

well I now own a 9.25 Edge HD :) Should arrive next week, as well as the G11

now to have fun buying all the other bits!

Assuming the G11 comes stock as it would directly from Losmandy, do I require a dovetail plate or anything like that to mount the scope?

Also are these good quality? http://www.deepspaceproducts.com/d-series-side-by-side-dual-dual_8_4234_8985.html

am thinking of widefield rig on one side (300mm lens/camera) and the edge on the other

[astro744]

Bintel sell the genuine Losmandy one. See http://www.bintel.com.au/Accessories/Dovetail-Plates---Adapters/141/catmenu.aspx

There is also an Orion model at Bintel for a bit less although I'm not sure if it is an exact copy. What you want to look for is what holes are pre-drilled and tapped in each plate to make sure it suits your needs. Also look at how the tightening knobs feel to turn and how well the clamps release. I've only ever gone with the genuine saddles not wanting to try the others just in case and the price of the genuine has always been reasonable.

I think you will have balance issues at certain angles with one heavy SCT on one saddle and a much lighter camera and lens on the other. You may be better off piggy backing the camera on top of the SCT.

[kkara4]

Awesome Astro thanks a lot for the link and advice! The balance issue makes perfect sense now that I think of it. I will wait till my Edge arrives so I can measure the holes in its dovetail to ensure I buy the right version :)

[Amaranthus]

You must be soooooo excited.

I've always bought genuine Losmandy saddles/mounting plates. I figure that these are 'buy once in your lifetime' items, so may was well get the best.

[kkara4]

I am indeed keen as!

I also share your mantra Barry, I have no intention of getting other than a Losmandy plate at the moment!

It would have been nice to buy a Nagler 31mm eyepiece as well, but alas that will stretch my budget beyond what I am willing to stretch beyond what I already have :lol:.

Looking forward to the learning curve as well, i think its fun playing with new toys (albeit a very expensive toy!)!

[Amaranthus]

A Panoptic 24 mm could be a good cheaper widefield eyepiece to secure in the interim. I also plan to eventually buy a Nagler 31 -- once I get to dark skies (which will be in a few months when I move to rural Tasmania). It gets spoilt by the wash-out effect of light pollution where I currently live.

[kkara4]

I will check out the Panoptic thanks Barry. Id rather just use the included EdgeHD one till I save up enough money again for the Nagler though :P

[el_draco]

I would be a little careful going SBS. It adds a degree in complexity when it comes to balance that I dont think is justified. You will also need to have a counter weight system to balance the scopes, despite the ability to slide the SBS on the mount head.
(eg) http://www.bintel.com.au/Accessories/Counterweights/Losmandy-Counterweight-br-DVDWS-with-2-5lb/1391/productview.aspx

You may find it easier/ cheaper to go for top and bottom D plates with radius blocks designed to fit your scope. Losmandy stocks all you'll need and you can get it through Bintel.

(eg) http://www.bintel.com.au/Accessories/Dovetail-Plates---Adapters/Losmandy-Celestron-9-25--Dovetail-Plate/606/productview.aspx

Losmandy also have various camera platforms you can use to mount the camera
(eg) http://www.bintel.com.au/Astrophotography/Astrophotography-Accessories/Losmandy-Three-Axis-Camera-Mount/1284/productview.aspx

Use the KISS principle as much as possible.

Rom

[kkara4]

Thanks for the reply Rom, the Edge HD i believe requires the DC925N dovetail, which is good because it is $30 cheaper than the one linked! I will double check when the scope arrives though :)

I will stick to the piggyback method then - with those radius blocks provided, do you just undo screws in the existing OTA housing and mount the blocks to them?

[el_draco]

The holes in the radius blocks match those in the OTA. Get rid of the orange bit of junk on the edge, flimsy and dumb. Couple of losmandy plates look good and are very rigid. The build is beautiful. When changing the plates over, go gently and undo from below. Any flakes of paint that come loose will come out the hole. when screws go back in, do this VERY gently, the threads are identical and there should be no binding.

Rom

[kkara4]

Thanks Rom, sounds good. Not sure what you mean by the orange part but sounds like ill see it once I have the scope in my hands!

[Camelopardalis]

Barry and I disagree on this :lol: but a 24mm Panoptic is not a wide field eyepiece in a long focal length scope :P

Stick with the Axiom/Luminos that it comes with...it'll have a wider field stop and show you more sky :thumbsup: and really, they're not as bad as they sound. Sure, it's no Nagler in a fast Newtonian, but it's well suited to a f/10 SCT.

[kkara4]

Thanks Dunk, Ill wack in the included one and see how things look! What makes an eyepiece "suited" to a particular telescope?

[Camelopardalis]

Optical design...telescopes inherently have field curvature and it depends on design, focal length, etc as to how much. This can cause the image to be out of focus at the edges while in focus in the centre, i.e. the focal plane is not flat.

From what I understand (not much!) - and there are experts here that know way more about this than I - eyepieces can also exhibit field curvature and the combination of that from the scope and the eyepiece can either cancel each other out or make it worse, depending on design parameters. SCTs typically have a fair bit of field curvature so it's speculated that the eyepieces Celestron supply have taken that into consideration by design.

Needless to say, this is probably further complicated - or maybe not - for the Edge HD scopes, which have the correcting lenses in the baffle tube to help give them a flatter field i.e. the focal plane is less strongly curved so that the edges and centre are closer to or are at focus at the same point.

I've oversimplified here and I'm sure there are other factors too...

[Amaranthus]

If you observe with the f/6.3 FR/flattener fitted, then you get a nice wide, flat field. It is great for visual in addition to AP. Then take it out for high power (if you want) or planetary, where the FC is irrelevant anyway.

[kkara4]

1) Prime focus: Canon 5D --> CWT-2070 --> RAD-1074 --> Baader Visual Back 3.25 Clicklock
2) Powermate 4x: Canon 5D --> CWT-2070 --> RAD-1074 --> Powermate 4x 2" --> Baader Visual Back 3.25 Clicklock

These are Televue part numbers that John Rodes suggested from Televue. Anyone see any glaring issues with this on the Edge 9.25?

[Camelopardalis]

I'm pretty sure you're going to need a spacer for prime focus at least, as the back focus will be nowhere near optimal. Check out the Edge HD white paper, I'm pretty sure it lists 146mm for all except the 8" Edge.

[astro744]

Interesting why John did not recommend the PTR-4201 adaptor as follows:

2a) Powermate 4x: Canon 5D --> CWT-2070 --> PTR-4201 --> Powermate 4x 2" --> Baader Visual Back 3.25 Clicklock

The only thing I can think of is the CTW-2070 does not fit the PTR-4201 in which case you would need a third party Canon T-Ring as follows:

2b) Powermate 4x: Canon 5D --> Canon T-Ring --> PTR-4201 --> Powermate 4x 2" --> Baader Visual Back 3.25 Clicklock

I'm sure both options work and maybe you get vignetting with the standard T-Ring option especially with a full frame 36 x 24mm camera.

Maybe ask John out of curiosity if you are likely to get vignetting with my option 2b) and also ask what is the magnification factor with his option 2), (not using PTR-4201). Is it still 4x?

Addendum:

Maybe ask John when is the PTR-4201 recommended?

[kkara4]

Astro, in my haste to post this up while rushing to do other things, I forgot to mention he did in fact suggest the PTR-4201, in the configuration exactly as per your 2b). However, since you use a standard T ring in 2b) dont you get vignetting as you say?

He specifically suggests the RAD-1070 method for prime focus stating that it will help reduce vignetting, so I assumed this would also be best for the powermate added in as well!

I will ask him both of your questions Astro, will see what he says. He doesnt seem to want to reply anymore :(

[kkara4]

Dunk, I have asked him this exact question in my latest reply to him, will see what he comes back with :). It may well be the case that he suggests going the PTR-4201 route to add the effective extension length it provides

[killswitch]

I didnt need a spacer to achieve prime focus with my DSLR and C8. The T-ring/adapter from my refractor just went straight into the Clicklock.

SCT's have plenty of focus travel.

[kkara4]

thanks Edison, I was doing more reading this evening and a few people on CN have similar thoughts. I am really thinking of going for the 2.4" route as opposed to the standard T ring. I will give Televue a call directly in the morning to finalise things.

[Camelopardalis]

I'm just quoting their white paper, where they're specify a tolerance of 0.5mm, as hard as it is to believe.

With my refractor, incorrect spacing was really obvious in the captured image (once I got it on my computer screen). I use the Celestron T-adapter with my C8 so it's already at the right spacing...or so I'm led to believe :lol:

[Amaranthus]

I don't use a spacer on my C8 with a DSLR either. I just go Visual Back --> T-Ring --> DSLR and it comes to focus with plenty to spare.

[kkara4]

thanks Barry/Dunk.

So this morning I got on to Televue, didnt quite catch the fella's name, but he was more than happy to provide advice...ended up being a 25 minute conversation :P.

He brought up the EdgeHD white paper on his computer and we had a chat.

He advised that it is always better with an SCT to have the camera further back than the specified prime focus distance as opposed to too close to the rear cell, but otherwise there is plenty of range at which focus can be achieved.

Lets look at prime focus photography first:

As stated by the white paper (page 13), T mount to sensor distance for DSLRs is usually 55mm. This is the same for the CWT-2070. The RAD-1074 adds about 3mm to the overall length (it has a very thin shoulder). Now on page 13/14 of the white paper, it can be seen that the Large T Adapter adds 91mm of extension from the rear cell, so with the 55mm standard T-sensor distance you get guess what 146mm. The Baader visual back provides a lot less (not sure how much) extension, so the Televue gentleman recommended the use of a X3C-0009 3.5" (88.9mm) 2" extension tube, thus getting me very close to the 146mm mark.

It sounds to me like Celestron want you to get it to the 146mm mark to get you in the middle of the forward/back focus range of the mirror.

The gent also recommended the use of their ACC-0003 2" visual back, where apparently the ring from the celestron diagonal threads onto so that you dont need a 3.29" to 2" thread adapter. However this is 2.1/4" long, so i dont think the 3" extension would be required, he then suggested the X2C-0008 2" extension, which again gets me close but slight further back.

So for prime focus full frame DSLR, his recommendation and my preferred option is:

Baader 3.25 Visual Back --> X3C-0009 --> RAD-1074 -->CWT-2070

Now his comments about the powermate 2" sizes were interesting. Apparently there may be an issue with inserting the powermate in place of the X3C-0009 above (or in between the X3C and RAD), because the glass element of the powermate would be too far physically from the camera sensor. There may also possibly be a problem with internal reflection. The gentleman recommended this instead:

Baader 3.25 Visual Back --> X3C-0009 --> Powermate 4x --> PTR-4201 --> standard Canon T ring.

Although the T ring is 42mm, because it is much closer to the glass element of the powermate physically, apparently there will be minimal vignetting. If I try the CWT-2070 and RAD-1074 combo with the powermate, then I would not need the extension tube (and ill have the CWT-2070 and RAD-1074 anyway), so I have a number of options to test out. I still feel ill get vignetting with the PTR-4201 though :question:

[kkara4]

John Rodes reckons the Baader 3.25 visual Back --> Powermate --> Rad-1074 --> CWT-2070 would still work though (approx same total back focus distance). I will confirm this with him as soon as I can. Havent even got to the diagonal yet!

[astro744]

Very informative! Thanks for filling in others on this forum with so much detail.

You probably spoke with David Nagler (Al's son) or the man himself, Al Nagler. They are full of knowledge and always ready to help sort out any issues and give good advice.

Don't be too surprised if in time you end up getting all the options and then you can tell use what works best. Extension tubes and adapters always come in handy and you can often use them on other telescopes. I've invested in multiple adapters, some I hardly ever use but they're there if I do need them.

Since you've done your homework and very well too, go with the recommendation and see what results you get.

[kkara4]

cheers Astro, I was thinking the same thing, just buy it all and sell what I don't find I need later!

Now I just need to confirm the visual back detail with Dunk, and then figure out what to do in terms of a Diagonal - the way I see it the Diagonal can be used in place of the extension tube since it is itself an extension of sorts, but then with a powermate hanging on the end it might want to always rotate like a big lever!

I have a feeling it was Al, because I heard the word "Al" in the earpiece and then there was a little break in the line, and maybe I was confused because I was expecting to hear more than just "Al" :lol:

[Camelopardalis]

Yeah it's interesting to see what sort of focal length the Powermate is introducing. The other thing to consider is that at the focal length you'll be at with the Powermate inline is such that the vignetting may be minimal, but also if you're imaging at f/40 then the chances are you're mostly interested in the bright planetary object in the middle of the field :D

Given what you're spending, chuck in the Celestron one (http://www.optcorp.com/ce-93646-t-adapter-for-9-25inch-11inch-14inch-edgehd.html) for sh*ts and giggles...it's inexpensive and simple.

Don't get me wrong, the TV stuff is nice...really nice, they always make good stuff, but it 4 pieces when 2 would do? :shrug:

Likewise, the Baader stuff is good quality stuff too. They really think about their target market. I use their visual backs on both my Edges.

[kkara4]

Thanks Dunk, and thanks for the PM!

Another interesting thing, apparently you can have insertion depth issues with visual backs on the 9.25 and 14 edge, because if you look at the white paper you can see the lens elements in the baffle tube are right near the threaded opening. For example, you cant use the Astro-Physics maxbright diagonal in their 3.25-2 visual back for this reason, it doesnt fully insert.

Not sure how much "taller" the baader is compared to the Astro-Physics though (I forget which edge you have Dunk!)

[Camelopardalis]

I use the Baader visual back and I've just got a tape to it and it's 54mm (give or take) long, from the base of the thread to the 2" aperture. So long as the nose of the diagonal isn't longer than that, you should be OK. Likewise the powermate.

I've just measured the protrusions on the parts I use, and the Everbrite nose is 35mm, the Baader diagonal 25mm, and the 2.5x Powermate 37mm (no idea what it would be for the 4x though :( ). Unscrewing the visual back, the thread is 13mm long (give or take)...

So for me, I get... 54mm - 13mm - 35mm = 6mm ... so the nose of the Everbrite diagonal is 6mm away from the outside end of the thread.

Obviously, this doesn't cause me any concern with the 8" or 11", but the 9.25" does seem to have the correcting lenses much closer to the end of any of the scopes :help: but so long as the thread is the same length/depth, and the Powermate insertion depth isn't more than 40mm, you should be OK. This ignores any additional spacer you might use of course.

[killswitch]

Did he happen to mention the downside of having it so close to the cell?

[kkara4]

Thanks a lot Dunk! What is the length on the baader visual back from the opening to the top of the thread shoulder then? This measurement i know ill be good with. I am 99% sure the 2x powermate is exactly the same insertion depth as the 4x.

Also here is a reply I just received from John Rhodes:

Krishan,
The SCT can focus from with-in itself to 3 feet behind it. you won’t need an extension tube of any sort.
You would on other scopes though…

Well there is less chance of vignetting wit the CWT and you need it anyway for Prime focus… Why have two connectors.

The light that leaves the PM leaves it as Parallel light rays this is the beauty of the PM’s here is the approximate change for every inch
if you were to add any.

http://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_app

You see the 2X is negligible and the 4 has a very small increase of less than IX and all this is at 4 inches of extension.

The CWT and RAD1074 is just as short as the Powermate T ring adapters and a standard T ring. Or very close.



John Rhodes

Technical Sales Rep.
Tele Vue Optics Inc.


So looks like I wont be bothering with the PTR-4201 and associated T ring, and this will simplify swapping between setups (prime focus, powermate, visual and visual powermate) greatly. Also looks like I wont be bothering with the extension tube from John's reply.

Dunk do you find you can get focus just fine on your 11" no matter what combination of tubes/diagonal/powermate you use?

[kkara4]

He did not, but looks like John has cleared up all the issue anyway! But then I come across things like this:

http://www.celestron.com/c3/support3/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=2427

so in the end I think I will just get the extension tube as Astro said, and sell it later if needed!

[Camelopardalis]

The thread is 13mm depth, and the visual back threads on all of it.

I've not used my C11 for DSO imaging yet, only planetary...focus is easy with a bahtinov mask, although to be fair it's fairly straightforward with the big rubber knob as it allows relatively fine focus movements.

The issue as I understand it with the back focus is because the field of the Edge HD isn't perfectly flat, Celestron only specify that it's 3x flatter than a conventional SCT. This means that away from the optimal back focus distance, focus across the whole field is harder to achieve. I'm less likely to notice this with my aps-c sensor, but as you're full-frame you're more likely to find it an issue.

[kkara4]

After a few rainy/cloudy days and battling the flu/some other nasty bug which pretty much confined me to bed for Friday and Saturday, finally had the strength to put the G11 together, install the losmandy dovetail on the OTA and have a little go at using the hand controller for Gemini 2. Only thing I did was enter my GPS coords and date and time.

Took the scope outside at about 6pm, 7pm put it all together on the lawn in about 5 minutes chucked the astrozap dew shield on (no heater), found Saturn as quick as I could and just watched it:eyepop: for about 15 minutes. This was through the stock Celestron eyepiece. No problem picking up Titan, Dione, Tethys and Rhea. The clarity was incredible. At 100x power though couldnt make out any detail in the rings/on the disc.

I really dont like the Celestron eyepiece though, I find it really awkward to look through properly, but when I do get the angle right it is a great view! Anyway all the Televue stuff is on its way, so when I get all that ill chuck the camera on there and probably sell the Celestron eyepiece :D.

And to top it all off, i decided to take a pic with my phone (Galaxy S2) through the eyepiece, adjusted curves slightly in photoshop, and am stoked with the result I got just with that crude method!:

http://i1186.photobucket.com/albums/z377/kkara4/Space/20140622_192556_crop_zpsd966758c.jp g

At about 8pm (about 1 hour after setup, 2 hours after cooldown start), the corrector started misting up, and the body started to get wet as dew started to condense on it. Even the finderscope and eyepiece started to mist by the time I had packed up. All the grass started to get wet as well. I looked up the history of dew point/air temperature and they came very close together at this time, so I suspect that even if I had a dew heater I would have been done regardless. Humidity was >90%. All the previous days rain probably didnt help the situation!

Ah well it is good to know what the extreme limit is, and im stoked that I got as long as I did with it outside. Going back inside was no problem, house was heated to >25 degrees so the mist evaporated in a matter of minutes :)

[Camelopardalis]

Nice one mate, glad to hear you're feeling better :)

I've had mine a few years and it came with the Axiom LX 23mm and it's a nice enough eyepiece. Not sure if it works with the same way with the Luminos (assuming that's what came with your scope!), but if you twist the black rubber band around the middle of the eyepiece, the face pushes out making it much easier to use IMO.

Regarding dew, I find with my 11" once it gets beyond mid-80s I'm on borrowed time..I need a better dew solution for that one. The 8" keeps going like a champ though...hopefully your 9.25 will prove more like the latter. Still, without a shield and heater you were lucky to get that far with that humidity ;)

[kkara4]

Cheers Dunk, I had the shield on, so probably pretty normal considering...at least I know what the limit is now!

Yep I have the push out thingy ill try using that next viewing session...pretty sure its the Axiom you speak of (23mm) :).

Will start looking into a DIY heater solution, can easily make one up. Also want to start adding some temp sensors and things to measure mirror and tube temps...hmmmm

[Camelopardalis]

There's a local business opportunity :D

[kkara4]

haha :P. Way too busy unfortunately with other ventures :P.

Great success tonight. Connected ethernet cable to hub, got all the computer controlled Gemini stuff working, then interfaced it successfully with Stellarium!

Spent a few minutes messing about moving the mount around and practicing slewing the scope to point to various things. I suppose the accuracy will be very dependent on the settings ive programmed the Gemini with in terms of time and location, and also my polar alignment.

Next thing to try will be setting up a VPN, and logging in to the network via laptop, on which Stellarium and appropriate drivers and things are installed.

Step at a time :thumbsup:

[kkara4]

well the Televue stuff arrived yesterday, such unbelievably high quality made gear. Held in the hand is like holding a great big hunk of gold :D.

The CWT-2070 and RAD-1074 were the right choice are my initial thoughts. I screwed them together and there is roughly 30mm between the glass element of the powermate and T ring shoulder. I havent managed to figure out the total optical path length through the everbrite or Celestron diagonals yet, but am pretty sure I wont need the Televue 3.5" extension tube, so will probably sell it after testing to make sure I dont need it. Initially I was thinking of using it in place of the diagonal for prime focus, but this will be extremely awkward, so I think I will always use a diagonal no matter what.

For now I have to use the Celestron diagonal till the Baader clicklock arrives (hopefullly this week!).

Last night seeing was poor so didnt bother taking the scope out. I dont think I can contain myself today though, I wanna see Saturn at 400x powaaaaaa. haha. then i might even try photographing it with the MK III at 200x power.