RC's: Which model is best for DSLR work?

[Star Hunter]

Guys, I'm looking into getting an RC scope for full frame DSLR work.

So far I've looked on the Net at Rock Mallin's 12" F8 from Canada, the pending 16" GSO, the Meade LX600 14" ACF or a 14" F6.3 Dall Kirkham from Orion Optics in the UK.

I see big Mike has the Orion 12" AG 12" F3.8 and WOW! what images he takes!! buutt.. when one has a limited budget, not everyone can afford their dream scope/camera (mine is a 24" F8 APO refractor)

So having woken from my dream, what RC brand? do you think is best for DSLR (not CCD) work?

Ta, and clear skies to all..

James

PS: To my old mate Paul Haase, what do you think cobber? You have an RC scope. What's your thoughts?

[Paul Haese]

Hi Jim,

I reckon you have to buy the best one you can afford at the time. If you can afford one of the good ones then go for that. I like my GSO 12" and it has very good optics despite some detractors here saying there must be a problem because I have not done much imaging with it. My agenda is to get my automation sorted on my smaller scope first before sorting it on my RC12. After which people will see more images coming from my RC12.

My only comments with the GSO gear is the focusor is not up to par, you have consider buying a top grade focusor for these scopes. Feather Touch or Moonlite and nothing of lesser quality. The cost of these focusors is significant and that will add to the overall cost of the project. You want to be able to use focusmax with the focusor down the line too as focusing RC's is a pain by eye. The 12" has a ali tube which should have been truss design. I don't know if GSO plan on a truss system as I am seeing carbon fibre tubes being mentioned at Andrews, but the current design can be seen as problematic.

The Meade is not an RC design. It is something entirely different and has its own issues. Dew as you would know can be a problem with a large corrector. Orion optics gear is good, but remember Mike Sidonio has a 12" Newtonian. Not an RC. If might be something you might want to consider if you want to do more wide field imaging and allows for some narrower field imaging.

Deep sky intruments also make an RC, as well as Officina Stellare. These are all cost orientated, but excellent telescopes made for doing research grade work as well as excellent imaging.

I would also consider forgetting the imaging with just a DSLR. To really image at any RC's potential you really need a mono camera for such a scope. A full frame sensor is what you should be looking for here or the 16803 sensor which is like two full frames put together or you could go with the 6303 sensor which is perfect for mosaic work. I am using an STL11000M on the RC12 if that give you any indication, and my NGC253 image is a crop as pointing was quite a bit off.

However, you choose try to spend a bit of time thinking about the issues. What mount are you planning on using? You will need a beast of a mount to make imaging with a long focal length worth undertaking. You should consider buying an second hand PME on Astromart and shipping it out here. I do know of someone here that is selling their PME but they want 12k for it. Its a good mount with little use. A PME is really what you want with a 16" RC. It will be a huge scope and very heavy.

Best of luck finding the scope you want. Feel free to ask me any more questions that you might think pertinent.

[Star Hunter]

Originally Posted by Paul Haese

Hi Jim,

I reckon you have to buy the best one you can afford at the time. If you can afford one of the good ones then go for that. I like my GSO 12" and it has very good optics despite some detractors here saying there must be a problem because I have not done much imaging with it. My agenda is to get my automation sorted on my smaller scope first before sorting it on my RC12. After which people will see more images coming from my RC12.

My only comments with the GSO gear is the focusor is not up to par, you have consider buying a top grade focusor for these scopes. Feather Touch or Moonlite and nothing of lesser quality. The cost of these focusors is significant and that will add to the overall cost of the project. You want to be able to use focusmax with the focusor down the line too as focusing RC's is a pain by eye. The 12" has a ali tube which should have been truss design. I don't know if GSO plan on a truss system as I am seeing carbon fibre tubes being mentioned at Andrews, but the current design can be seen as problematic.

The Meade is not an RC design. It is something entirely different and has its own issues. Dew as you would know can be a problem with a large corrector. Orion optics gear is good, but remember Mike Sidonio has a 12" Newtonian. Not an RC. If might be something you might want to consider if you want to do more wide field imaging and allows for some narrower field imaging.

Deep sky intruments also make an RC, as well as Officina Stellare. These are all cost orientated, but excellent telescopes made for doing research grade work as well as excellent imaging.

I would also consider forgetting the imaging with just a DSLR. To really image at any RC's potential you really need a mono camera for such a scope. A full frame sensor is what you should be looking for here or the 16803 sensor which is like two full frames put together or you could go with the 6303 sensor which is perfect for mosaic work. I am using an STL11000M on the RC12 if that give you any indication, and my NGC253 image is a crop as pointing was quite a bit off.

However, you choose try to spend a bit of time thinking about the issues. What mount are you planning on using? You will need a beast of a mount to make imaging with a long focal length worth undertaking. You should consider buying an second hand PME on Astromart and shipping it out here. I do know of someone here that is selling their PME but they want 12k for it. Its a good mount with little use. A PME is really what you want with a 16" RC. It will be a huge scope and very heavy.

Best of luck finding the scope you want. Feel free to ask me any more questions that you might think pertinent.

Mate, thanks for reply. I appreciate it. I have a new Titan 50 that currently swings a C14 'fastar' and a Gstar EX2 video cam. Guiding (again by video) if need be, is through a Konus 5" F8 g/scope. Sky X Pro controls the lot.

Not sure of the weight of the GSO 16" RC. Some say it's around 38kgs, so that mount should handle that mass if I go that way. The tube rings of the GSO scopes are too thin to my liking and had to get a set of rings from Joe at Parallax. The GSO RC 16" may have to be the same.

I agree. ALL RC's should be trussed but in my case being out in the sticks, we too get dew and dust. Whereby a full tube is fare better. I do see the Mallin 12" RC's are ribbed inside and I have not seen others over 10" that are ribbed. The GSO 16" tube from what I've been told, is Ali or metal. This runs parallel to what a mate of mine said, a few weeks ago from his trip back from Taiwan, saying they and the Chinese have problems making good quality, CF tubes.

Perhaps those with ribbed reflecting scope tubes can wade in here and tell us what they have noticed, over non-ribbed internal telescope tubes?

As for a CCD camera, I've checked out SBIG, FLI and Apogee and like all things in life, it comes down to $$$'s and priorities. So until I win Lotto, I'll do what I can with what I've got.

As for those focusers you mentioned, I'm going to check them out. While Crayfords are nice looking and neat, they may not be the way to go on an RC.

Maybe someone else who has an RC, can wade in here and give us all a 'heads-up' on critical focusing of the RC?

Unlike a full classical cassergrain like have which has a late '90's AP 2.73" focuser, focusing is a breeze. Any other system that has a tight foci, can be a real PITA, particularly with CCD and Digital.

So I'll keep you posted mate, as to my journey through the heather and avoid selecting a Scot Thistle.

Jim

[Paul Haese]

Feather touch makes a rack and pinion focusor which is suitable for autofocus. The moonlites are also good for autofocus too. The lift capacity is what is required.

Don't overlook the QSI cameras too. The new series 700 might just suit the needs of camera, but like you said get what you can first.

[RickS (Rick)]

I run a FLI Atlas on my GSO RC10 and that works very well indeed. They aren't cheap but they are fantastically accurate and I use the same focuser on several different scopes.

At f/8 or f/9 the CFZ is not that tight. The main thing is getting a focuser that is rigid under the weight of your imaging payload - close to 10Kg for me now

Cheers,
Rick.

[swannies1983 (Dan)]

I've got an 8" RC and use it in combination with a modded 30D (check my history). It has the standard focuser and I've had no issues with the setup. I haven't imaged much lately and don't plan to for a while due to work commitments.

[gregbradley]

I've had a 12 inch RCOS and have a CDK17 which is a corrected Dall Kirkham.

I was a member of the Orion Optics Yahoo Forum and followed it for some time. Not sure what the status is now but at the time I was following it to follow progress on OO dall kirkhams they were really behind on production. There was one guy in Spain who finally got one and it had a problem with the corrector. I believe OO handled it promptly (they seem pretty responsive).

There was a German guy who ordered a 14 inch ODK and I think in the end he was happy but the scope took ages so I would check that out.

Firstly, guiding. Using a guide scope with a long focal length RC will be problematic. Guide scopes are OK up to about 1500mm. Beyond that you start to get problems with differential flexure meaning something bends slightly to do with the guide scope/guide camera and the main scope so the corrections are not 100% valid anymore. So you really want a through the scope type guiding solution. Off axis guiders are the usual solution for that or self guiding cameras like SBIG or their latest versions.

Planewave Instruments 12 inch CDK is a good scope. There was a scope called the Hyperion by a US maker. They had a backlog on delivery also but that was some time ago.

As mentioned by Paul there is also Deep Sky Instruments. Carbon fibre is really the go with RCs as at long focal length you don't want expansion and contraction issues. I find my CDK is quite good that way - the scope's focus does not change much over several nights. The RCOS was even better at that.

A smaller but powerful scope is the Takahashi BRC250. That is now called the CCA250. Built like a tank and a bit heavy but its F5 and I got a lot of good images out of it. It also works well with a KAF8300 chipped camera being F5 and 1260mm focal length.

I have no experience with the GSO RCs but there are plenty of super images from 10 inch RC owners.

One caution I would add for long focal length RC. You really need decent seeing to get the most out of an RC. You can do narrowband to overcome light pollution but bad seeing is another matter. Seeing is always an issue with imaging but it does not affect a Tak FSQ106ED hardly at all but at 2 or 3 metres it can make a big difference.

So one way of working out which scope is best for you is to look at various images others have produced a make a note of which ones you like the best. Then what equipment did they use. Then modify that with your budget first then your seeing and light pollution situation. Then you can make an informed choice.

Also talking from experience, it pays in the long run to get a smaller amount of high quality gear than getting cheaper gear, not being happy with it, taking a big loss selling it and then end up getting the better gear later on. Good gear often sells later for not much less than you pay for it. Especially now if the price is in US dollars and our dollar does fall further.

Greg.

[Star Hunter]

Originally Posted by gregbradley

I've had a 12 inch RCOS and have a CDK17 which is a corrected Dall Kirkham.

I was a member of the Orion Optics Yahoo Forum and followed it for some time. Not sure what the status is now but at the time I was following it to follow progress on OO dall kirkhams they were really behind on production. There was one guy in Spain who finally got one and it had a problem with the corrector. I believe OO handled it promptly (they seem pretty responsive).

There was a German guy who ordered a 14 inch ODK and I think in the end he was happy but the scope took ages so I would check that out.

Firstly, guiding. Using a guide scope with a long focal length RC will be problematic. Guide scopes are OK up to about 1500mm. Beyond that you start to get problems with differential flexure meaning something bends slightly to do with the guide scope/guide camera and the main scope so the corrections are not 100% valid anymore. So you really want a through the scope type guiding solution. Off axis guiders are the usual solution for that or self guiding cameras like SBIG or their latest versions.

Planewave Instruments 12 inch CDK is a good scope. There was a scope called the Hyperion by a US maker. They had a backlog on delivery also but that was some time ago.

As mentioned by Paul there is also Deep Sky Instruments. Carbon fibre is really the go with RCs as at long focal length you don't want expansion and contraction issues. I find my CDK is quite good that way - the scope's focus does not change much over several nights. The RCOS was even better at that.

A smaller but powerful scope is the Takahashi BRC250. That is now called the CCA250. Built like a tank and a bit heavy but its F5 and I got a lot of good images out of it. It also works well with a KAF8300 chipped camera being F5 and 1260mm focal length.

I have no experience with the GSO RCs but there are plenty of super images from 10 inch RC owners.

One caution I would add for long focal length RC. You really need decent seeing to get the most out of an RC. You can do narrowband to overcome light pollution but bad seeing is another matter. Seeing is always an issue with imaging but it does not affect a Tak FSQ106ED hardly at all but at 2 or 3 metres it can make a big difference.

So one way of working out which scope is best for you is to look at various images others have produced a make a note of which ones you like the best. Then what equipment did they use. Then modify that with your budget first then your seeing and light pollution situation. Then you can make an informed choice.

Also talking from experience, it pays in the long run to get a smaller amount of high quality gear than getting cheaper gear, not being happy with it, taking a big loss selling it and then end up getting the better gear later on. Good gear often sells later for not much less than you pay for it. Especially now if the price is in US dollars and our dollar does fall further.

Greg.

Hi Greg,

What you (and Paul) said makes sense. While price governs quality, there's no substitute for aperture and having been there and done that over the years, the Planewave, Orion UK, ASA, Officia Stellare and a host of international brands in the semi to pro fields, makes me think it's best as you said, check out what others use and what they have achieved then draw up one's conclusions there then then. I'm still buying Lotto tickets.. lol..

Thanks mate.

James (Jim)

[CDKPhil]

Hi James,

Another thing you should consider is the corrected field of the telescope.

If you are using a full frame sensor, DSLR or other, You will want a minimum corrected field of 52mm. There is no point using a full frame sensor if you have to crop the image because of aberrations etc. Check out the manufactures spot diagrams and compare them.

I can vouch for the Plane Wave 12.5, it is very well made and corrected.
I have not had to touch the collimation once since receiving it over a year ago.
It is quite expensive but as Greg has already said it is better to get something that is going to do the job straight up, it will save you money in the long run.

Cheers
Phil