A GSO 12" F4 with 3" focuser

[h0ughy]

i just saw this advertised at Andrews? a 12" F4 for astrophotography - what a great new toy to play with and the price under a grand!!! Could this be too good to be true? would like to know more about the focuser etc.

12" f/4 3" M-LRN Astrophotography-optimised OTA reflector
(300mm x 1200mm) Has strong and smooth 3" diameter linear focuser $999.00

[gbeal]

Likely the same as the Astronomics AstroTech 12" Huff. I have the AT8", a stunning scope, and outstanding value for money.
If there is a fly in the ointment, it is the collimation, F4 is a magnitude more demanding than my other newts (F5).
Gary

[h0ughy]

http://www.astronomics.com/main/product.asp/catalog_name/Astronomics/category_name/W783G2XG7GFD9G312JK1P6GQ65/product_id/AT12IN

thanks Gary

[gbeal]

Pretty sure it is same beast Dave, or a very close cuzzie.
Biggest beef is the sheer weight, it isn't light, and will tax many a mount.
Maybe the 10" would be more user friendly, but like I said to me the 8" is the sweet spot. Hopefully the "mods" had to make to get the AT8" running nicely will now be standard fare in the later models, the 12" F4 especially.
Bit more info on the Astronomics site than what you posted at the start, and it is interesting to note that it is back-ordered anyway, so the "April" guess from Andrews is likely right.
Gary

[robz]

Nice scope.
Pity about the weight......rolled steel tube............madness ? :screwy:
I guess that brings the price down though. O.K if you have a Paramount:rolleyes:

[erick]

6" - 12" f4 OTAs are listed on the Guan Sheng Optical site:-

http://www.gs-telescope.com/

No details or photos, however.

[casstony]

I reckon it won't be long before carbon fibre tubed versions are available, either from GSO or Synta. A 12" f/4 carbon fibre newt is in the Skywatcher catalogue along with a bunch of other yet to be released stuff, some of which was shown at Astrofest in London earlier this month.

[robz]

Not meaning to be an , but so did a number of 5 element apochromats, the EQ7............now becoming an EQ8:question: :confused2:..................none of us are holding our breath as it seems that this ''new stuff'' is science fiction.........or might as well be before we get it here in Aus. :rolleyes::shrug:

[casstony]

Holding your breath is not a good idea but the new gear will be here eventually - patience :)

The bigger 5 element apo's are actually triplets with a flattener on the focuser.

EQ8 at Astrofest: http://www.youtube.com/watch?v=Mg6WLerTKZg

[Waxing_Gibbous]

Its a shame about the weight. Given that the cost of CF tube in China / Taiwan is much less than in the US or Europe, you'd think it would be at least an option.

[multiweb]

The specs sound real good but I'd love to see a corrected CCD field on that thing with the coma corrector/flattener advertised. Similar systems (well corrected) cost an arm and a leg.

[casstony]

Found this about Astrofest:

On display at the Optical Vision Ltd stand at this year's Astrofest will be the following new Skywatcher products:

Skyliner-400P 16" Flextube Go-To Dobsonian, a prototype of the forthcoming EQ8 Synscan Go-To mount, the SkyTee-2 Dual Alt-Azimuth mount, the new QUATTRO-series f/4 Carbon-Fibre Imaging Newtonians and ED150 3/5 Element Apochromatic Refractor.

[robz]

Looks exactly like the defunct EQ7??.
I like when he mentions it's a comparable to an AP900 or 1200 !!!:lol:....................yeah... .........o.k........;)

Sorry hOughy..............got carried away with the language there mate.............won't happen again.

[robz]

Hopefully the Skywatcher tubes will be comparable in price and will probably be just as good?

[RobF]

The really nice thing about a Newt vs RC is the with the shorter F ratio you get a nice FOV, tracking a bit easier and really suck down the photons (not to mention price!). I'm biased, but I still think 8" is a sweet spot too until exotic tube materials become the norm. Great to see the focuser, flocking etc getting well need attention. Presumeably a bigger 2ndary too. Would need a good set of collimation tools I guess.

[robz]

I have an 8 inch F4 astrograph newtonian.
It's capable of revealing a lot more than it should in light polluted skies - M42 is stunning:eyepop:
However, with it comes a huge secondary, thick secondary vanes, coma city and very careful collimation required.:rolleyes:

[gregbradley]

I had a Vixen RS200 F4 Newt and I could not collimate it. Then I got one of those cheap laser collimators and collimation was reasonably good within 5 minutes.

You need a good coma corrector. The Vixen one seemed OK for small chipped cameras perhaps up to a DSLR. Baader makes a MPCC coma corrector which is popular.

Perhaps a 3 inch Wynne corrector from Philip Keller may be the go for the 12 inch.

Greg.

[Tandum]

That will cost more than the scope .. ouch :sadeyes:

[gregbradley]

Yes, I thought of that after I posted it. Your right, it probably would cost more than the scope.

Baader MPCC then.

Greg.

[Moon]

According to the Astronomics web site the focuser is 3.3 inch, not 3 inch.

[Moon]

Bintel now have it listed for $999 and Andrews have since dropped the price to $899.
Still a lot of basic information is missing: size of secondary, design of primary mirror cell, amount of backfocus available...

[renormalised]

They're not going to list that on a site like Bintel...you'd have to ask the guys if they knew the full specs, which they may or may not.

[TrevorW]

Take one GSO 12" f/4 add carbon fibre tube with some baffles and you have one cheap astrograph
Google Astro-tech 12" f/4 for further details

[alistairsam]

Hi,

I've been seriously considering getting the 12 f4 OTA from andrews.
will have to call them for the weight and secondary size.

but wouldnt a 2" coma corrector suffice as if you're using a dslr, the coma corrector would be only an inch or so from the ccd chip of the dslr or the focal plane, and at that point, the light cone wouldn't be over 2". just guessing.

I wonder if it would be possible to cut out sections of the OTA tube to make it lighter, but still retain stiffness. anyone done anything like this?

other option is to buy just the mirror and build the rest.
is it possible to get a decent mirror cell for a 12"? any recommendations?

[Satchmo]

Bintel list it at 18.4kg without rings or mounting plates- so I guess you can bank on 25kg by the time it is all kitted up to take exposures ( with guidescope and rings , camera etc)

I noticed that they will have their own branded coma corrector available for it soon too.

[Moon]

The Eagle has landed.
To give you can idea of the size, it just fits on the back seat of my car.
For the record, Andrews website currently has it listed at $799 and Bintel at $999.
That's about all I can say at this stage.
James

[Zaps]

Now this is going to be interesting! Please keep us posted.

[Terry B]

The scope is not big, you just clearly just need a bigger car.:P

[Moon]

First impressions posted here:
http://deepspaceplace.com/at12in.php
I'll update this page as I progress. The first step will be to stabilise the OTA under the focuser.
James

[gbeal]

Great to hear about this James, watching with interest.
A shame to see that the issues that were exposed with the AT8" (of which I see you have as well) haven't been addressed. The collimation system on the primary is farcical, one set pushing, and one set pulling OK, but not when they are "apart", as all it means is the cell twists or alignment is altered. I simply removed the "push" knobs on my AT8".
Again, the AT8" focuser base area is pathetic, I made a stiff metal reinforcing section that helped the stiffness of the tube. And that is with the AT8" with a 2" (Feather Touch in my case) focuser.
Baffles or flocking on the agenda soon?
Regards,
Gary

[Moon]

It needs some flocking. I like the plastic baffles in the AT8IN, too bad they are missing here.


I did the same to mine, and I added some bigger springs I got from Cost Less Bolts. The difference was amazing. Will do the same again this time.


Can you share a picture how you did it? I'm open to ideas. I also had to do this to my AT8IN and I plan to do it the same way this time : put a big sheet of Aluminium inside the OTA, curve it around, cut a hole for the focuser and secure with lots of stainless steel bolts, and paint black. It worked a treat last time, but this is a bigger tube and it moves a lot more - but only in the direction at right angles to the tube. Length wise it's ok. It's made worse by the grub screws on sides of the base of the focuser - it rocks on those too. But the base is also moving. Added together it moves a lot. The focuser itself is fine - for example the focus lock does not impact the collimation at all. :)

James

[steve000]

it could be deliberate..

I have a 12" skywatcher with steel tube and about 70% of it is on the focuser side of the center of the dovebar attachment point.

so much weight is in the mirror and assy.. only about 10% of the scope actually sticks out the back from the rings. if it were CF maybe there would be too little tube to attach to the rings... maybe

[gbeal]

Elegant it is not, but it does work. If the weight is significant, and the flex objectionable, maybe a complete circle of stiffener, sized to be a tight fit within the tube? Mine I simply secured with the Feather Touch attachment bolts.
Gary

[Moon]

Thanks Gary.
I tried a large thin sheet of Aluminium. I tested it last night with the Catseye XLK installed, but it didn't work. Still lots of movement in the tube. I'll see if I can find a thicker sheet like yours.
James

[tlgerdes]

Have a look at Mike Sidonios 12", it has a brace around the outside near the focuser. You could get another set of tube rings and do the same, then drill and screw or rivet the the tube to the tube ring.

[Moon]

Trevor,

I really like that part of Mike's scope - for me new rings will be plan "C". Before I added the Al sheet, I moved the rings really close to the focuser as a test and tightened them up as much as possible (but no screws / rivets) - it made no difference at all.

I've just got back from Bunnings, this time I have 3mm instead of 1 mm Aluminium. Hopefully this will be enough.

James

[strongmanmike]

James

If it helps and in case you haven't seen it, you can see the inside of my tube here (http://www.pbase.com/strongmanmike2002/image/132998031/original) and the rings here (http://www.pbase.com/strongmanmike2002/image/133046310/original)

Cheers

Mike

[Moon]

Thanks Mike, it looks very solid. Would be nice if they were all built that way in the first place...

[Alchemy]

My 3c worth, large tubed newtonians are just plain difficult to work with. The flex in the tube. Lack of strength in the area surrounding the focuser.
For 1000 all up throw the focuser away and buy a decent one.
Wind effect on the tube whilst imaging.
It just goes on and on.... Been there done that.

If you must use one of these creations then do yourself a favor and get an SBIG with built in guide chip, or perhaps a large off axis guider.

In reality someone needs to rip out the mirror and cell, start again with a custom made truss setup.

Edit.... Mikes scope cost a lot more than these so you'd expect it to be a better unit ( my critique for unit doesn't apply)
Clive

[Moon]

True, but those extra rings are non standard even for Orion, which was the point of my comment.
James

[Derek Klepp]

Just to let you know not all is myth I have just received my 16" Skywatcher GOTO Dob from My AStroshop and although a light shroud for it will have to be home made it is a very nice and large scope and the views are great.Simple to put together and easy to operate.I'm not the most photogenic person however

[Alchemy]

Hmmmm perhaps I haven't given due attention to all the details throughout the thread......
Anyway, having used a 12 inch gso newt for imaging for quite some time, I would not have another go in the configuration it is sold in.... Try by all means, but having been through the process myself, the scope needs a LOT of work to make it a really viable imaging scope.

[Moon]

I just posted a Youtube video (http://youtu.be/TTGCutUicp4) showing how I tested the OTA wall strength.
It's a lot better now with the 3mm aluminium reinforcing, but still not perfect. When the tube is vertical (i.e. pointing at Zenith) it hardly moved at all.
James

[alistairsam]

wow, did'nt realize tubes flexed so much. nice and simple test. would you know what the weight of the camera is?
i'm guessing it would flex a bit less when the camera is in the focuser as the load would be distributed across various points along the drawtube and there would be less torque at the top end of the focuser, for this test it is concentrated at the top edge of the focuser.

[Moon]

The camera is about 2.3kg.
It's a very sensitive test - there's a cool animated gif on this (http://www.catseyecollimation.com/autocol.html) page that shows the relationship between what you see and the error expressed in degrees.
Remember almost all the movement is from the OTA tube wall, and not the focuser.
James

[bmitchell82]

Well I use the qhy9 which is a DSLR size chip and the MPCC keeps it flat edge to edge. it doesn't matter if the light cone is bigger than the MPCC, as long as enough light is getting to the sensor, eg, if your MPCC sucks in say 80% of the 100% light cone you wont loose anything!

As for the Secondary on a 12" F4 if it isn't around the 90mm size you will probably loose out due to vingetting or your illuminated circle will be small hence light drop off will be a issue. My 10" is running a 70mm secondary with approximately 27% Central Obstruction and i have measured with CCD inspector about a 7% light fall off in the corners on the 40d it got to just on 10% so im pretty much using 100% of the 254 mirror's capacity.

If the focuser is anything like the Linear 3" or 2" focuser seen on most GSO scopes... bad news and you will most likely be upgrading very quickly so add a extra 400 bucks to that budget. once again its all good to have a f4 newt, but if it isn't collimated then your off to comet ville! Tube droop kills your collimation/ location of the MPCC! bad joo joos

My 10" has close to 120mm of back focus which is good for a OAG, FW, CCD, MPCC. As for collimation, the only way to do it isn't with a laser it only gets it rough, if you want to do it right Cats eye auto collimator, sight tube and collimated cheshire is the only way to be cirtain that your scope is bang on and preforming well and oh it doesn't have to be cats eye, but a Autocollimator is very advisable! The last thing is the collimating gear on the scope mirror cell and secondary. if its like the skywatcher standards for secondarys... :( if they have made them thicker and given them beef then Kudos!

As for flexure... All newts suffer! like Clive has already said you need OAG or SBIG tech to quell the angry mobs! hence what i did! OAG with a 3"FT focuser. the tube doesn't flex that much at all around the focuser due to the secondary vanes that are tight as a guitar string strengthing the circular hollow section!

Sometime soon i will be writing a little novel about my travels and findings for making a cheap newt work like a good quality astrograph.

Brendan

[Moon]

Brendan,
The secondary is 87mm which is a bit on the small side. A bigger problem is the location of the focuser. It's too close to the primary - so the CCD is too far away from the secondary and this causes unnecessary vignetting. The 8 inch version had a similar problem.


Yes you should!

James

[bmitchell82]

the vingetting is more than likely coming from the secondary being too small On the standard skywatcher 254mm dobsonian the fully illuminated circle came in a a whopping 6mm..... at 78mm for the 12" F4 like i said you would be looking a minimum of 90 odd mm to start getting close, but more like 100mm to do the job properly!.

Have a look at this image (http://brendanmitchell.net/?page_id=10&album=15&photo=59&occur=1) Just to give you a idea thats close to 400mm from the OTA surface to the sensor + about 150mm to the secondary! It missed out on focus with a Starlight adaptive optics unit + Starlight OAG + QHY9 and filter wheel! by about 5mm.

Im only talking with experience on my own rig but i have done alot of reading and looking at the designs for it. I have even designed a 8" F4 GSO mirror newt and that required a 70mm secondary to get a 20mm 100% illuminated circle! which doesn't even cover my qhy9 properly.

Brendan

[Moon]

Small update: The 3 inch Wynne corrector arrived and I got to try it out last night. Luckily it fits in the focuser like a glove. I had to add a few grub screws to the focuser tube to hold the corrector in place - but it wasn't too difficult. Because the corrector extends the full length of the focuser drawtube (and then some), it seems reasonably secure.

When focused on a star, the bottom of the corrector is almost exactly level with the OTA wall - i.e. perfect.
So even though the focal point **seems** a long way out, it is in fact ideal for the 3 inch corrector. To put it in perspective, the corrector is 137mm long and the focal plane is 58 mm out from the end of the corrector. So the focal plane is around 195mm out from the OTA wall.

So yes the only realistic option to improve the vignetting in this scenario now would be a bigger secondary.

James

[Satchmo]

James

My calculations suggest the nearest commercial size 4" minor axis secondary to get 100% lighting to the edges of the KAF 1100 chip, with the 8" back focus from tube wall. A good source would be Antares Optical. You will probably need to replace the secondary holder and spider as that supplied does not look adequate to support a piece of glass like this.

[Moon]

Finally! Weather and work have been unkind over the last month, but I have managed to get my first image with this scope:
http://deepspaceplace.com/show.php?id=ic4628

I'm really happy with the coma corrector - no halos or reflections I can spot.

James

[strongmanmike]

Pretty good, you should be happy with that James :thumbsup:

Are there pictures anywhere of what you have done to the OTA?

Mike

[Moon]

Not yet - I'll post some on my site soon. All I've done so far is:
- one strip of aluminum inside the OTA under the focuser
- a few tiny grub screws in the focuser tube to hold the coma corrector in position (I had to remove the compression ring becaase it was too small)
- dew heater on the secondary
- I **think** I put stronger springs in the primary cell? My memory isn't what it used to be...
- robo focus (after that picture was taken)

All in all not too many changes. Now I just need to spend more time on it. For example, last night I finally got Focusmax and all that v-curve stuff working properly after lots of mucking around.

The more I look closely at that image, the happier I am with it.

James

[Satchmo]

James

What kind of coma- corrector are you using ?

[Moon]

The 3" Wynne from ASA (http://www.astrosysteme.at/eng/correctors.html)
I also got them to make me a custom adaptor of the correct size for my camera.
James

[Satchmo]

Just having a look at your picture full size your system seems to avoid those unsightly halos around brighter stars evident in pictures taken with the Orion AG12. I suspect that the halos are caused by poor ghosting analysis in the design of the corrector ( but I'm open to other suggestions) , which the Keller corrector seems to be free of.

[strongmanmike]

Well Mark there is more to it than that actually.

Firstly ghosting in a corrector lens system usually manifests in images as odd reflections that appear in the frame somewhere and not as halos around stars themselves...or perhaps you were referring to something else?

Halos around stars of various shapes and sizes can be caused by a number of things, including: the focuser barrel, adapters, chip cover slip, the CCD window, the filters or the corrector and the coatings on any one of the optical surfaces near the chip, or in some cases a combination of some or all these factors. As a result different combinations of scope corrector/flattener, filter, CCD window and chip cover slip give different results with different filter makes and even different filters within a single brand line.

The halos you are refer to in my images I have noticed are present most prominently when using the Ha filter and to a lesser extent the OIII and SII and they are weaker in the R G and B filters and basically non existent in the Lum. Now the intersting thing is that my Lum filter is a brand new not released Astronomik filter that Gerd Neumann sent me to try - this low halo effect is evident in my recent M7 image actually and I would say the degree of haloing in this bright star data set is no worse than many FSQ and other optical configuration images I have seen ;)

If you also care to take a look at Adam Jesionkiewicz and Peter Shah's and other AG users work (http://www.orionoptics.co.uk/customergallery.html) who use various combinations of cameras, adapters and filter brands (but the same corrector), you will see your theory about the Orion Optics corrector being the culprit is likely not accurate.

Mike

[gregbradley]

There was a lot of internet posting about reflections and halos about 2 -3 years ago when the first Apogee and FLI 16803 chipped cameras were released.

The STL11 chip is half the size of the 16803 so you are not comparing apples with apples there and the reflection debate started with the 16803.

It seemed to mainly be prevalent with scopes that use correctors.

To be clear that is all scopes with a 16803 chip. Even an RCOS. An RCOS probably could get away without using one but it would lose its tight stars further offaxis which the correctors/flatteners fix.

The usual fixes were:

1. A new range of antireflection coatings on filters (Astrodons were some of the worst offenders as they are mirrored type filters) So you now have several offering Generation 11 filters. I use Astrdon Gen 11 filters and those coatings work well.

2. Cameras had aperture masks installed.

3. Apogee and FLI offer no cover slip versions of their cameras as these can cause small halos around stars.

4. CCD Window needs to have antireflection coatings and be of good quality material. FLI addressed this very well.

5. Edges of filters need to be blackened. Baaders need to have the blackening extend onto the face of the filter 1mm as the coating ends just before the edge (a different manufacturing approach).

6. Most reflections seem to bounce off the correctors/flatteners and the filters and then bounce around anything not nailed down reflection wise. As Mike says any bright parts, anything anodised (highly reflective in IR).

But the biggest fix seems to be the choice of filters.

So if you are thinking of getting one of these cameras chose the filters carefully. They don't all perform the same.

Greg.

[Satchmo]

Thanks for the detailed discussion on halo causes, guys. I wonder if surface roughness on the filters could be causing some near field scattering as well ?.

Mike: Proper ghost analysis requires an examination of both on axis and off axis ghosting. It seems clear from your results and from others that its a filter/ camera issue rather than the corrector.

[Moon]

I don't have many data points from personal experience, but I have looked at a **lot** of images online and I see halos or whatever you want to call them in images taken with ASA and Orion newts, including the people mentioned by Mike above. Guess which image in the attachment is from an ASA 12" and which one is from an Orion AG12?
I was fully expecting this when I ordered my coma corrector and I won't be surprised if and when it happens. So far, it hasn't.

[strongmanmike]

Yeh that's right, not sure what the issue is with them anyway, every telescope/corrector/CCD/Filter system shows some sort of particular star aberration, halo or out of field rays etc anyway.

Oh and the left image is the Orion the right image is the ASA :thumbsup:

Mike

[Moon]

Go to the top of the class!

[strongmanmike]

Ha ha I have an incredible memory for images too ;)... the left image is with Adam Jesionkiewicz's Orion Optics AG12 and the right image is with Florent Poiget's ASA N12

:thumbsup:

Mike