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New imaging scope


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Hi,

I'm considering buying a new scope for imaging with my SX H694 ccd camera. The scope will be mounted on my AP1200gto mount in my observatory, which at the moment houses a heavely modified Vixen R200SS f/4 reflector. My primary interest is galaxy imaging.

I'm currently looking at either a 12" ONTC f/4 Newton from Teleskop Service (http://www.teleskop-express.de/shop/product_info.php/info/p5017_TS-12--f-4-ONTC-Carbon-Tube-Newtonian-telescope-1-8-Lambda---fully-customizable.html) or a 10" or 12" RC telescope from Altair (truss tube, version 2).

Do any of you have experience with the two scopes above?

Any other suggestions? 

ASA and the larger OOUK AG scopes are over my budget, which is around £4000 max.

The scope has to work (almost) out-of-the-box and I don't want to spend every night tweaking the scope to get round, pinpoint stars. (Maybe an apo instead? :-o )

Kind regards,

Helge

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If you want as little tweaking and upkeep as possible then an APO refractor is the way to go. BUT you said you want to image galaxies so in order to to get the FL you would want to image galaxies at you would need at least a 6-8" Apo and those will be over your budget. Also since you are wanting to image galaxies then you will want as much FL as your mount can handle properly. Since you have an AP1200 then I think you will be cover for a LOT of FL. With galaxy imaging your dont really need to worry about the F/ratio as much as you would if imaging nebula. (There's the whole f/ratio myth here that we could talk about but dont want to get off track) So don't be afraid of imaging with a F/10 scope. With your budget and mount you could easily afford a 11" or 14" EdgeHD. The 11" has 400mm more FL than the 12" RC and is WAY less, especially if you go second hand. And I think the extra 400mm of FL would get you more resolution than the 1" of aperture, especially when you factor in that the secondary is much larger on a RC than a SCT. Your budget and mount would even fit a 14" EdgeHD and have plenty of spare cash and your mount would have no problem handle its FL either. I've seen people image with 16" scopes on the AP1200 so you have a lot of options to work with.

I would not suggest the 12" Newt bc it only has 120mm FL vs 2800 that the 11" Edge has. And again with imaging galaxies FL is going to be your biggest friend. Now if you are still wanting some wide field imaging options for some of the galaxy cluster or groups I would suggest getting a scope like the 11" Edge and then also a 4-5" Apo that you could mount tandem and just swap the camera between the two. This would give you a lot of options to chose from in terms of FL. 2800mm @F/10, 1900mm @F/7, 800-1000mm @F/6-8, and if you are feeling adventurous you could go with the hyperstar option and get ~400mm @F/2. Though Im not a huge fan of the hyperstar because it can be very tricky to work with it is an option. Make sure you do some research on this if you think you would be interested. Those options are with the SCT and Apo in tandem btw.
 

There couuld be other brands and options out there too that other might suggest. This is just the way I would go if I where you and your budget. I'm currently saving for an AP900 with 11"Edge for galaxy imaging after doing almost a year of research on my options. My budget is a lot less than your though and all my purchases will be second hand as well. Dont be afraid of second hand as you can save a lot of money this way.

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With the small ccd chip of the H694 (10x12.5mm, 4.54 microns pixels) the 11" EdgeHD would give a very small FOV of approx. 12x15 arcmin and a pixel scale of 0.33"/pixel, meaning extreme oversampling. The 14" would be even worse. And I'm not very fond of SCT due to mirror flop.

I have actually just sold my C14 (not EdgeHD), because I didn't find it very suited for DSO imaging with its 4000mm focal length and non-fixed mirror. This is why I considerer the options above. Shorter focal lengths and fixed mirrors. A 1200mm focal length will give me a pixel scale of 0.78"/pixel, which is quite good for my seeing conditions. 

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Firstly mirror flop can be taken care of very easily. You have to buy a focuser and attach it to the back and just inable the mirror lock. And by focuser I mean one that is standard on all other telescopes not just that silly dial that moves the primary back and forth, which is why theres mirror flop.

Im still pretty new to CCD so I cant really advise you too much on that, sorry. But if what you say is correct then yes the over sampling would be a problem. But if you are really wanting to image galaxies I still think 1200mm is a bit on the short side, thats my opinion only obviously. I would try to strive for around least 2000mm. If you are really wanting to get detailed images of galaxies the more FL the better, factoring in your seeing and CCD limits of course. If the two RCs match up with your CCD well then I would suggest going that route over the Newt. The only thing that is going through my mind on those RCs is that are the truss design really worth the added price? With you having an AP1200 the weight savings that the truss design gives over the normal tube design isnt an issue anymore. So not sure what advantage it has over the tube design. Maybe cool down time? But if its in an obsy that shouldnt be a huge problem to begin with right? There could be other advantages but I just dont know enough about them to give a good solid opinion on it. Maybe someone else can give some better imput on it. If you go with a tube design you might be able to stretch to a 14" which would give you plenty of native FL and even with a reducer still give you a good amount.

Check out astrobin and look through the images there and filter them to show scopes in the 1200mm range and taken with a CCD that has a chip about your size. Will give you a good idea of the FoV you are dealing with.

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Hi,

I'm considering buying a new scope for imaging with my SX H694 ccd camera. The scope will be mounted on my AP1200gto mount in my observatory, which at the moment houses a heavely modified Vixen R200SS f/4 reflector. My primary interest is galaxy imaging.

I'm currently looking at either a 12" ONTC f/4 Newton from Teleskop Service (http://www.teleskop-express.de/shop/product_info.php/info/p5017_TS-12--f-4-ONTC-Carbon-Tube-Newtonian-telescope-1-8-Lambda---fully-customizable.html) or a 10" or 12" RC telescope from Altair (truss tube, version 2).

Do any of you have experience with the two scopes above?

Any other suggestions? 

ASA and the larger OOUK AG scopes are over my budget, which is around £4000 max.

The scope has to work (almost) out-of-the-box and I don't want to spend every night tweaking the scope to get round, pinpoint stars. (Maybe an apo instead? :-o )

Kind regards,

Helge

What do you wish to image target wise that is?

A.G

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As far a I have read, the truss tubes are more temperature stable that the solid tubes. I think, I also read somewhere that they hold collimation better.

However, I think the TS Newtons look as they are of better quality than the GSO RC clones. TS uses Orion Optics mirrors (research grade), 7mm thick carbon tubes from Klaus Helmerich in Germany and also mirror cells made in Germany.

But still, the questions is which of these scopes will work best out-of-the-box - I don't want to modify too much. Maybe I should just go the refractor route :-)

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If you are really interested in galaxies I really think you are going to be under whelmed if you are going to image at 1200mm. At least I would feel that the scale of the galaxies would be too small for my liking. Maybe you dont mind the wider fov with your galaxies.

Have you looked at the GSO 10"/12" truss RC? A member on here "recently" bought one and installed it in his obsy. You can find his thread here that shows the build. You could PM him and ask some questions. Im not sure if he had to do a lot of tweaking or not but hes posted some really good pictures lately. I know the truss design allows better temp control/cool down of the scope but what about in an obsy? I would think temp would be better controled in the first place in an obsy so the temp change wont be as dramatic. Is your obsy a ROR or a dome design?

And don't get to taken off by tweaking. All scopes need some tweaking out of the box (well besides fracs). But, as you have said, if the build and design quality is good you should only have to do a major tweaking once and then after that little tweaks now and then. And by tweaking I mean getting collimation right and balance perfect and other sort of things that would be required with any new scope purchase. With your budget you should be able to get a scope that doesnt require any major mods to make them work.

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The majority of galaxies require a decent focal length to get the required image scale on the CCD. A medium/fast Newtonian scope might also be a help with imaging times. So I wouild be thinking a 12" F5  Newtonian scope giving around 1500mm FL. The focal length of F4 scopes might be too short for galaxies? RC scopes are interesting but optically slower and more testing of the mount and guiding- but that will become critical anyway if you are to get maximum detail.

With any mirror based a certain amount of tweaking and pre-session collimation will be required- just part of the 'pleasure' of owning one of these instruments I'm affraid. Long focal imaging is out of the realms of plug-and-play astrophotography!

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If you are really interested in galaxies I really think you are going to be under whelmed if you are going to image at 1200mm. At least I would feel that the scale of the galaxies would be too small for my liking. Maybe you dont mind the wider fov with your galaxies.

Have you looked at the GSO 10"/12" truss RC? A member on here "recently" bought one and installed it in his obsy. You can find his thread here that shows the build. You could PM him and ask some questions. Im not sure if he had to do a lot of tweaking or not but hes posted some really good pictures lately. I know the truss design allows better temp control/cool down of the scope but what about in an obsy? I would think temp would be better controled in the first place in an obsy so the temp change wont be as dramatic. Is your obsy a ROR or a dome design?

And don't get to taken off by tweaking. All scopes need some tweaking out of the box (well besides fracs). But, as you have said, if the build and design quality is good you should only have to do a major tweaking once and then after that little tweaks now and then. And by tweaking I mean getting collimation right and balance perfect and other sort of things that would be required with any new scope purchase. With your budget you should be able to get a scope that doesnt require any major mods to make them work.

Very interesting thread, thanks. The GSO truss RC's are the same as the Altair truss RC's I'm considering, so yes, I have looked at them ;-) 

I don't mind tweaking if it means collimating once in a while, etc. What I meant is, I don't want is a scope that I will have to modify a lot to get it working properly (e.g. change mirror cell, springs, focuser, etc.) or that will require adjustments every clear night.

A 12" f/5 Newton would probably be easier to collimate, but it is quite a beast and it may be too long for my observatory (Pulsar 2.7m). 

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The majority of galaxies require a decent focal length to get the required image scale on the CCD. A medium/fast Newtonian scope might also be a help with imaging times. So I wouild be thinking a 12" F5  Newtonian scope giving around 1500mm FL. The focal length of F4 scopes might be too short for galaxies? RC scopes are interesting but optically slower and more testing of the mount and guiding- but that will become critical anyway if you are to get maximum detail.

With any mirror based a certain amount of tweaking and pre-session collimation will be required- just part of the 'pleasure' of owning one of these instruments I'm affraid. Long focal imaging is out of the realms of plug-and-play astrophotography!

Galaxy imaging and nebula imaging are two different things. They typical fast f ratios do help when imaging nebula because of the majority of the faintness of the object and the low surface brightness. This does help pull as much data out with as little total exposure time but if you have seen some of the recent M1 images that have been posted they where taken at F/10. When imaging galaxies, because of their surface brightness and that they are point source lights, the fast f/ratios don't come into play as much as it does for nebulas. So if the primary targets are galaxies, which for the OP they are, then dont let an F/Ratio be your deciding factor. The FL is what you really want to be considering. 

I thought the GSO and Altair where the same but wasnt sure. I've heard decent things about them but they are still relatively new to the market so there aren't a ton out there. Pop over to a couple other forums and poke around. Maybe someone has posted a review. From what i've seen they seem to be of a better build quality so I dont think you'll be needing to modify anything. The only thing I would be hesitant on is the focuser. Most stock focusers dont do well with the heavy weight of most CCD imaging trains. Especially when you start imaging near the zenith. Im not 100% sure on the focuser though so do look into it. I think most people tend to replace stock focusers anyway.

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My primary interest is galaxies. 

The RCs will be the right choice but working straight out of the box is another matter as I am sure that they all need quite a bit of tweaking before they come on line. The only scopes that I know that more or less work out of the box are the top grade APOs. Perhaps you could have a look at those and probably a few SCTs.

A.G

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I know you've tried SCT's and haven't got on well with the mirror flop, but I can confirm that the new mirror clutches work on the C8 Edge at least. I've not needed to refocus my C8 Edge unless I'm changing cameras! 

I'm not sure how well the clutches work on the larger Edge HD's, they might not be so good due to the extra primary mirror weight?

Still the C8 Edge might actually suit you? :)

1) pretty much works out the box ( I just tweaked the secondary once when I first got it and nothing since)

2) 1422mm f/7 or 2032mm f/10 plus. (the reducer on the 8" doesn't cost the Earth like the 11")

3) completely flat field!

4) very compact.

5) No diff spikes (not that they bother me personally)

An RC would also be a great choice from what I've heard, not sure how easy these are to setup though?

Edited by Chris Lock
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It seems that most people recommend an RC due to the long focal length (> 1500mm) for galaxy imaging. However, I think it is important to also consider the pixel size of the ccd chip in this calculation, so the pixel scale is optimal for the seeing. Don't you agree?

Using a 12" f/4 Newton with a focal length of e.g. 1200 mm will give me a pixel scale of  0.78"/pixel using the Sony ICX694 chip (pixel size 4.54 microns), which seems quite optimal. Using a 12" RC at f/8 (focal length of 2400mm) will give me 0.39"/pixel, which is heavely oversampled for my typical seeing of 2-3". However, I can use bin2, which will give me 0.78"/pixel, i.e., the same as with the Newton, but the FOV will be the half. Since both scopes are 12" the same amount of light from the object (e.g. galaxy) is gathered and hence, the same amount of light from a given part of the object reaches each pixel (or binned pixel) of the ccd if the pixel scale is the same.

So from this, the 1200mm focal length seems to be the optimal with my seeing due to the larger FOV - or am I wrong? Anything I missed?

I cannot exploit the high resolution a long focal length RC scope can give me with the small Sony pixels.

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Yep agreed, its one of the reasons I suggested the C8 Edge + .7 reducer :) 1400mm isn't that much longer than the 1200mm you are thinking of. I use a modded 350D with my Edge which gives me 1 "/pixel.

The big 12" f/4 Newt you're suggesting sounds good, quite bulky though, and you need to be well sheltered from the wind?

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Laser_Jock (SGL member) uses a 12" f/4 Newt for imaging, it might be worth having a word with him :)

Indeed I do! But if I was mainly interested in galaxies I'd still be thinking about the longer focal length 12" F5 instrument for the reasons of image scale mentioned above.

A with a 12" F4 (1200mm FL) on a DSLR sized chip the image scale is tiny. Great for extended nebulae but I had to do a rather severe crop to 'scale up' this image of M51.

DSIR6693_1024_zps8ed6f634.jpg

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I use an 8" RC with the small sony chip. My resolution is far away from what theorists say that it should be - But I have not noticed any issues. By all means consider theory, but in my experience, it is nothing worth more than idle consideration for the few. I get out there and take images and so far it seems to be going OK.

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Also dont forget that the RC's can be fitting with a reducer. So a 12" is native ~2400mm FL but with a .7x reducer brings it down to ~1700mm. I think this would fit better with your chip. Also try and see if you have anyone local to you that has a similar long focal length imaging kit and see what they use and what they suggest. 

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Nice images - with both scopes. If I go the Newton route I will use my Paracorr comacorrector, which increases the focal length to approx. 1380 mm, i.e., not that different from the 1624 mm that the 8" RC has. The f/5 Newton is also tempting but just so darn long. I think it will almost hit the dome in my Pulsar observatory.

What I like about the RC scopes is the long back focus, meaning that I can start using an OAG. Does the truss version of the GSO RC have an improved mirror cell compared to the "older" ones? I've heard quite some bad things about the 12" RC's mirror cell.

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