off axis guiding

[monoxide]

hi guys,
i was wondering if an off-axis guider would be any good to me for use on the fs-102?
could this be used with the focal reducer somehow?

[AlexN]

I've used OAG's in a 102mm F/7 refractor, an 8" F/6 Newtonian, an 11" SCT and in an 8" RC... I think they are great tools to have, and I've rarely found an area of sky where I can't frame an image exactly as I want and have the guider find a usable star right there.. The trick is to have a very very sensitive guide camera. The QHY5/Orion SSAG will work in most of the sky.. I've only ever run into trouble twice using the QHY5 and OAG. I love to only need one scope on the mount when I image, as for setup and balance purposes, the OAG is a fantastically simple piece of equipment. Not only that, but it greatly reduces the overall weight on the mount, and ensures that you will not be plagued by flexture..

[monoxide]

yup, id like to try one just to lighten the load on the mount and make it easier to setup/balance, might be able to go deeper since im maxing out the mount at the moment.

next question is, the lumicon easy guider or the orion one?
the orion one sounds pretty good with the helical focuser for the guide camera, not sure if the lumicon has this?

[pmrid]

There are a couple of things about the Lumicon a I like and several I don't.
Like:
1. The fact that the internal prism is quite wide compared, for example with the celestron Radial Guider.
2. The fact that you can move the focuser assembly around PARALLEL to the optical plane of the scope. It helps to find those guide stars.

The don't likes:
1. The coupling to the telescope 2" compression ring adapter is rubbish. It is too shortr and is prone to slump. If you had a w" adapter with say 2 or 3 screws at 120 degrees then you can hold the OAG firmly. But as it is, only a slight bump will dislodge it. And because I have a couple of grand worth of camera hanging off it, this makes me jumpy;
2. The guide camera assembly cannot be indepoendently moved without also moving the imaging camera. By comparison, the Celestron Radial guider has the ability to swing the focuser around the main tune by about 140-150 degrees and lock it in. Thismakes for a lot of flexibility finding a guide star and means you don't ave to redo flats every time you move to another object.
3. The fitting at the back of the Lumicon makes it very hard to attach a Canon EOW style camera directly - because the flash assembly fouyls the focuser assembly.

I only have a Celestron OAG suited to a SCT so have't experimented wioth others but I find it is much better at dealing with guide stars than the Lumicon. I prefer the Lumicon overall becase it uses much less back focus.

I find that the OAG works really well on my 127 mm refractor. Stars are quite sharp and clear whereas stars in the 8" Newtonian tend to be somewhat distorted by coma and other optical effects that flow from the fact that the image is being snagged from the very edge of a mirror that has built-in coma because of being quite fast.

SO on a refractor, I say GO and for choice, I say borrow a couple of different types and see what works best with your imaging equipment. Depending whether you're using a DSLW or a CCD, you may go for different brands/designs.

Peter

[AlexN]

I agree with Peter.. Get a hold of a few if you can borrow them off people and see which you like... I've had the Orion, the Lumicon Easy Guider, the Celestron Radial Guider and some generic no name branded thing... The no name one was a monster pain in the bum.. The Orion was perfectly suited to my setup, being that its backfocus is matched to suit the Orion SS Pro cameras, and the Orion SSAG (QHY5) so focusing these two cameras together was a dream.. However the problem with this for me was that I could no longer get the correct spacing between my camera and the MPCC, so it was either have perfect focus in both cameras with no mess, no fuss, or have a flat field of view... Naturally, I opted for the flat field of view.. The radial guider was great in my SCT, until I put a 2" focuser on the back of it, then the radial guider was not suited, as it connects via an SCT thread. Sure, you could get a 2" to SCT thread adapter made up for it, but I didn't bother, I just moved on to the Lumicon Newtonian Easy Guider. I finally settled on the easy guider. As Peter mentioned It takes up very little back focus, and whatever short comings it has (mostly, the things peter mentioned) can be easily accommodated for..

Recently I've been considering going back to an OAG... Maybe its time for me to do that..

[Merlin66]

I like some of the others have tried most of the available OAG. My need was something to help guiding the spectroscope. I have Meade SCT's and a couple of ED80's, so there's always the choice of 2" or SCT fittings. ( BTW on the refractors I found I could machine an adaptor which screwed onto the end of the drawtube (M55) and has a SCT male thread). Makes using something like the Celestron OAG much easier.
Using the #1209 zero shift focuser means going for 2" fittings anyway.
The best I've found so far is the Lumicon Newt OAG followed by the Orion Deluxe. I agree the Lumicon has some issues but certainly does the job.
All my gear ALWAYS has a safety strap fitted - to hold everything in alignment (no sag) and stop things falling to their death!!!

[coldspace]

Alex,
Was that ST10 you sold to Mark a self guiding one?

Whats your thoughts on these self guiding St's for ease of use?
I don't have a guide scope so when I make the next plunge deeper into imaging these self guiders (from the sbig site) sound really good.
I was thinking of getting one in the new year to help and maybe discover with S/Nova discoveries with upto 1 minute exposures as they are high QE but if I want to do some imaging with narrowband and RGB will need to guide so these sound like they will be good at long focal lengths?
I was looking at either the ST8 self guider or maybe even the ST10.

I read that these self guiding chips don't like narrow band filters but Astronomik put out a range of Narrowband thats suited for the Sbig line self guiding.
Have you had or heard of experiences with these filters and self guiding?


Regards Matt.

[AlexN]

Matt, My ST10 was the XEI model, no self guiding chip.. However my ST-9E was self guiding, and I can tell you now, I can not wait to go back to a self guided SBIG... If you want a setup that only requires one scope, and you want it to be easy to use, Go get yourself an SBIG... My ST-9E was capable of self guiding through a 13nm Ha filter without a worry, I did 2 second guide exposures with the guide chip at bin 2x2 and never had a single trouble finding a guide star... From what I understand, the newer ST cameras have a much more sensitive guide chip than my old ST-9E, so this could only mean that provided your Ha filter is not too narrow (read : 3~4.5nm) you should be able to self guide without an issue.

Definitely if you're looking to do s/nova searches with short exposures, the ST10XME is the tool for the job... It will excel in that field, whilst still offering great resolution and field of view for "pretty picture" photography. The ST10XME also has one of the most sensitive sensors available today with a peak QE of 95%, you really can't go wrong...

Just for reference, Im looking to get another ST10 in the next short while, and at the moment with the STX series set to be released very soon, the prices are becoming very reasonable.. Optcorp in USA have a sale going, buy the ST10XME for $4995USD and get a CFW9 filterwheel for just $390 more.. Can not go wrong.

Yes sir... I like SBIG self guiding. I like it a lot!

[coldspace]

Sold!!!!!!!!!!!

You just confirmed my thoughts on these wonderfull cameras. I should have the funds by Feb/March, once I get all my Christmas/family expenses done with.
I was looking for a option with just one scope and these ST10XME sound really nice with 95% QE. They also have a high QE across a large portion of wave lenght.
So when a friend of mine gets his next S/N I will be able to go image it easily.
I was after a camera like this as well so when I start doing some "Pretty Pics" in RGB and especially narrow band in my light hell hole with a resonable amount of real estate.
If I am going to spend this sort of money I want a camera that can do both tasks.
What focal length would be the fastest to image withon a 12 200R? with one of these chips before distortions would be apparant?
I use an Optec F7, F5, and F3.3 ultra wide reducers with my small Mallincam chip with no issues but with the much larger ST10's chip whats the formular to work out these things?

I have a hunch that F5 would be the limmit but with that much real estate on the ST10's chip maybe F7 compared to what I am used to with a DSI or Mallincam video cameras.

Regards Matt.

[AlexN]

I think you'd get away with F/5.. F/3.3 would be out of the question. F/5 may show a little distortion, but I suppose, its a case of cross that bridge when you come to it.. Or, take a few shots with a DSLR at F/5, the ST10 is approximately half the real estate of a Canon 20/30/40D.. So if majority of the field is ok on a DSLR sensor, you should be right as rain with the ST10..

You will not be disappointed with the ST10XME, Mine was the earlier XEi version, without the microlens on the sensor. This model had 30% less QE than the current XME model, and despite that, I've posted up a couple of shots, M16 and M8 that are 60x1minute exposures through a 13nm Ha filter...

I too loved the ST10 for its ability to shoot narrowband, as I image from fairly heavy light pollution most of the time... Which is also most of the reason I'm keen to get another one.. I'm still tossing up between the ST10XME or an STX8300 when they are released.. for pretty pics, the STX8300 is the better option, however no matter how much more real estate it has over the ST10XME, the super high QE of the ST10 keep drawing me back.. I could essentially get equal data with a similar field of view in the same time by doing a 2 panel mosaic with the ST10...

Cheers mate...

Alex.

[AlexN]

oops... heres those pics..

[coldspace]

also,

I know that the ST10 model has 17% more area than the ST8 but because it has 6 micron pixels compared to th 8's 9micron size would this make the ST 8 more sensitive but at a cost of resollution?

Would the ST8 suit my long focal lenght 12R better than the ST10 or would it not be too much in it other than area?

I note that the ST10 seems to be the perfect companion to a nice Apo.
Is the less resolution going to make much difference in my location in Brisbane?
I am mainly interested in imaging galaxies so maybe I will need larger pixels for sensitivity? but then more resolution may be whats needed as well:shrug:.

Thoughts on the two would be a great help in deciding.

Regards Matt.

[coldspace]

Wow, thats great sensitivity, the new model with 30%higher QE must be a treat.

What scope were these taken through?

Matt.

[coldspace]

I forgot about binning, I could just bin and get more sensitivity and still have room to move on the ST10.

Matt.

[marki]

Matt, you could always bin to make the pixels bigger or use a reducer. I think the optec next gen 0.7 would be ok for that chip as it can deliver a nice field up to 18mm. No good for my QHY9 though.

Mark

[coldspace]

Thanks for the feed back, don't tell my wife ;) you guys will you about my dreams for the new year.

I think we have gone of the OP topic (sorry for high jacking, you tend to get into discussions really easy) better get back on track on OAG's.

Regards Matt.

[AlexN]

The ST8's QE is lower than the ST10, QE is not just a factor of the pixel size, but also the inherent sensitivity of the CCD. The ST9E has 20 micron pixels, but is not as sensitive as the ST10XME.. Remember also that you can bin the ST10 upto 3x3 making the pixel size 18 micron, and still having 17% more real estate...

Oversampling is always better than undersampling in my opinion. Its better to have less than 1arcsec per pixel than 2arcsec per pixel as processing routines like deconvolution tend to really appreciate oversampled data.. not to mention that on nights of great seeing, you'll get better resolution.. I think the ST10 is the best choice of all the current SBIG cameras for what you're attempting to achieve.. The ST8 would be close, but not as sensitive, more noise, less resolution and only 1.6mp vs 3.2mp... When taking pretty pics MP is a big thing, its all well and good to have an image that looks fantastic, but if its not big enough to set it as a desktop background, or have printed out at least A4, then really, whats the point?

Yes, I was amazed at the sensitivity of the ST10XEi and my first thoughts were "imagine what it would be like with the XME! 30% more QE would have made a noticeable difference I think.. The scope I was using was a GSO 8" F/8 RC.. Unfortunately I never got a chance to use the ST10 in my TMB!.. I did however get a pic of M8 through my WO ZS70ED, This is attached to this post.. That was 60x1min subs with 13nm Ha also.. so again, you can see the sensitivity and resolution..

A great place for you to have a look at would be This Site (http://fredsastro.googlepages.com/home). Fred (Bassnut) on these forums used his ST10XME with his meade 12" LX200R scope at both F/10 and F/6.7 to deliver some breathtaking images.. If those pics dont tell you that the ST10 and a long focal length scope are a good match then I don't know what will! :)

[AlexN]

Ps.. Moving to self guided CCD's is not really off topic when you're talking about OAGs. Essentially the both achieve the same results through a different method.. Although yes, I think that this is all information that Tj simply doesn't need in his thread.. :) If you have more questions, perhaps make a new thread or PM...

Cheers.

[monoxide]

stop tempting me with self guiding ccd's!! :P:D

seriously tho if i had a choice between upgrading to a G11 and keeping my current imaging gear or sticking with the HEQ5 and spending the same amount on a new camera id definately take the camera.

back on topic though i think ill check out the orion OAG, its less cash to outay, looks a bit more user friendly and if i dont really like it then its not a big loss.

[pmrid]

A point I overlooked, in favour of the Orion, is the helical focuser for the guide camera. Getting te best focuse on the guide camera can be a fiddly business on most OAGs because it usually involves you manually sliding the cam up and down in the cradle while watching a live feed. And by the time you then tighten the 2 nuts to hold it in place, it has usually slipped a bit or the alignment has alters slightly so you end up with lesxs than optimal focus. The helical focuser is a plus. The other side of that coin is that once you have got your guide cam parafocal with your imaging setup, you don't have to move it again unless you change the imaging cam setup. So the helical focuser thingy is nice but probably not going to be the determining factor in your decision.

Peter

[AlexN]

too true there. With the lumicon i had to use a parfocalising ring to hold focus, and never really had sharp focus on the guider. It was pretty damn close, but never focused.. That said, guider focus isn't of all that much importance.. Although being able to get it close easily with a focuser would have been nice.

[Hagar]

I have been sitting watching this thread with interest since it began.
On topic, I have had a lumicon OAG and found i to be a real pain in the backside to use. A small guide scope is my choice when it comes to guiding.
Off Topic but in reply to the above quote, The most usefull item of any astrophotography set up is the mount. To forego a good mount for a camera is a sure fire recipe for disaster. The HEQ5 while a reasonable mount is really not up to the specs required for imaging with anything bigger than an ED80 and a light weight DSLR.

The other term which seems to be bandied about is the word real estate with regards to CCD imaging. The realestate spoken about must be taken in context of the imaging system used. It must be realised that every camera smaller than a full frame CCD suffers from a crop factor, the smaller the CCD the larger the crop factor and the narrower the apparent field of view you can image. In todays CCD market the ST10 has a quite small CCD and when used with long focal length scopes produces quite a narrow field of view.
When trying to image nebulas this can be quite restrictive even with some quite short focal length scopes.
I understand the QE of the ST10 to be brilliant but QE isn't everything extended exposure can and does help to pad out somewhat lower QE.

Just something to think about when looking at cameras, mounts and imaging systems in general. Nothing is clear cut and easy. Spend the time before spending the money.

[Merlin66]

The only difference between the self-guiding CCD camera and the OAG solution is that the camera has a built in OAG guide chip ( Usually the TC-211, the same as the original ST-4 guider.. large pixel size but quite sensitive)
The OAG, yes does take a little more work to focus, but no more than a guide scope... and when it's set up you can get as big if not bigger FOV to guide on, the choice of guide cameras (QHY5, DMK, Atik etc) and the flexibility of positioning the guide chip to suit the field. Some OAG allow you to pick off the guide star prior to the filters so there's no significant light loss to the guide star.
Even if you have solid guide rings and support, you still have focuser "droop" to contend with; at least the OAG gives you some hope...
My 2c.

[coldspace]

I am spending the time ATM to do lots of research on what I will end up buying next year to add to my observatory kit. This is why forums are my friend on doing research not just in my addiction in Astro stuf but my many other interests.
I am not really interested in doing large field imaging ATM as my intrest is in imaging small faint fuzzies so will need high QE and if I want to do pretty pictures then I will most likely need to use Narrow band anyway so high QE is good here.
The self guiding chip seems appealing to me ATM as its a one camera/scope system, I could then use a something like a light weight piggy backed 90mm Raptor for wider field imaging if I wished to get into it by just pulling the camera out of the 12R and plugging it into the piggybacked refractor. The AO system sounds really good as well and would suit this camera especially on a wedge mounted 12R to help a little to "sharpen up the images" from minor mount errors. Compared to what I am used to the ST10 has acres and acres of real estate.
My images that I get now are so bad I would not even bother posting them but I don't care as I like them and been not very "Tech" savy on this sort of stuff makes my learning curve so much harder but I usually always buy the right thing that suits me after lots and lots of research both on Astro toys and other things as well.
I agree, that the mount is everything, but for now my 12R suits me fine and in a couple of years maybe sell it and put a 14R on a AP1200 mount like a friend of mine uses which is so sweet.
I will be looking at all options for my next camera with all accessories under 10K and will probally buy in about 4 to 6 months after my homework has finished.
So be prepared IIS members for lots of questions coming up on user feed back on various cameras:thumbsup: over the next several months.
Thanks Doug for your feed back ,I have taken it on with interest mate. This is exactly why I like forums when doing research, feedback from both sides of the fence.
I don't just like hearing all one side as another opinion helps you make an informed opinion before spending big bucks on toys or whatever you do in life.
Thanks again.

Regards Matt.

[Hagar]

Matt, The post was not meant as any form of attack or similar, it was just some explanation of a few things often overlooked by many imagers when they are shopping for expensive equipment which has to do a wide variety of work in many diferent aspects of astrophotography.
Perhaps I better shut up. Lots of experts out there, just filter them well.

[coldspace]

No offence taken Doug:thumbsup:, I appreciate the feedback and was just trying to explain my needs but sometimes I rant a bit as its hard to explain thing via a key board.
Other than a guide chip camera which as I understand only S big has what other options would you recommend?
I have seen the Starlight express cameras in action and they work well.

Regards Matt.

[Hagar]

S Big are the only manufacturer with on board guide chips. I believe they have patented the feature. The on board chip does have it's drawbacks when you mention NB imaging. The fact that the guide chip is mounted behind the NB filters it can make it near impossible to attain a good guide star. The only way to overcome this is to either use a separate guidescope, camera or an OAG. QSI make cameras these days with quite a selection of cameras with a built in OAG or SBIG do sell a separate guide camera to use external to their cameras. This again requires something to guide image with. Other alternatives exist with cameras like the QHY range, FLI, Apogee. The list is endless and so is the selection of CCD's and cooling systems etc.
It really all depends on what scope, eg fl and the type of imaging you intend to do. Quality comes at a cost but some costs can be quite inflated.
Lots of questions to ask yourself:
What do I want to image?
What scope will I be using?
Do I want a OSC or Mono with filters?
Do I need a separate guide scope/OAG?
What sort of field of view do I want?
How much do I want to spend?

Good luck with your search.

[Merlin66]

Re the question of self guiding Starlight cameras.
I've had a MX7c with the STAR 2000 guide interface for almost 4 years and to be honest I couldn't get the STAR2000 to work for me... well to be fair - didn't try too hard!
In the UK, there are many imagers who still use the STAR 2000 and say it's the best thing since Vegimite ( well in their case Marmite)
The Y! AstroArt group is the best place to get information.
I use the MX7c on the spectroscope with a QHY5 as the guider.

[Bassnut]

I have tried external guide, self guide, OAGing and Ao at long FLs.

Each of these have advantages and show stoping disadvantages.

External guide is by far the most convienient and worth pursuing to the nth degree before before even thinking about the rest IMO. But the longer the FL, say over 2m the more you are forced to consider alternatives, but the much harder they get to use.

External guide allows composition of the target anyway you want, and you always get a guide star, point and go, but flexure just gets too much of a problem with exposures over 20min at over 2m FL.

SBIG internal guide is essentially impossible through NB filters unless you have a very stable mount with very low PE (eg a PME) that can get away with guide exposures of say 30secs or more, even RGB is difficult. And finding a bright guide star can be a very frustrating excerise, making composition tricky too.

Forget AO with internal guide unless useing just a lum filter (or none). AO is generally only of value if guide exposures can be 2 secs or less, otherwise there is no advantage over normal mount correction.

With internal and OAGing, manually rotating to find a bright guide star at long FLs is a painfull excercise, very hit and miss, and you have to wait till the rig settles down after bumping it, although as Alex mentions with OAG, widefield is less of a problem and a guide star maybe available without much or any rotation.

For OAG, I decided to use an autorotator for guide star searching, and that makes a huge difference, I can nudge and expose in quick succession with no disturbance.

I tried the rotator/TCFs focuser/MOAG/AO8/filter/ST10 on a 12" LX and found a showstoping problem I didnt think was going to be that bad untill I tried it. The image train is 350mm, the LX can focus, but stars are huge blobs :P. I dont know why yet, but I cant see anyway to make this work unless I make the train shorter. Perhaps removing the AO8 will help, but the focuser and OAGer(MOAG) are the longest items (and many adaptors), I cant get rid of them, that would defeat OAG. The rotator cant go iether IMO.

So if anyone is considering OAG on a SCT, youd need to be very sure the back focus distance can take it. Just the OAG, filter and cam would be OK, but at long FLs, not haveing a autofocuser and autorotator would be a pain in the butt IMO.

I fitted all the above to an RCOS (minus the focuser), shaved .2" off an adaptor, and it just perfectly hits BFD, no spacers, shear luck :). It all works very well, each item making the whole worth while.