RC or SCT?

[Spacedout]

Hello All,

I currently own a C11 XLT and I'm now thinking of upgrading to a larger size.  During my search for the next best thing I have seen a 16" RC Truss telescope from Altair Astro at a price that could not be achieved if buying a 16" SCT.  In fact the SCT would be considerably more in cost.  My problem really is having done a bit of searching I do not fully understand the pros and cons for either other than I can get a lot more aperture for a lot less if I take the RC Truss route.  Is there anyone here that might have or at least experienced both telescope types?  I'm assuming there are more cons to the RC hence the price difference but if the cons are not that bad then it may be worth the considerable saving.

Many thanks

Karl

[rwg]

I think Altair had the 16" RCT at AstroFest and it was quite a beast! Too big for an EQ6 very possibly...

cheers,

Robin

[nmoushon]

Firstly Im not sure if you are wanting this upgrade for imaging or visual. If you have the budget for this size scope you need to consider several thing, both for imaging and visual.

1.) Your mount is going to be undersized for either scope for visual and massively undersized for imaging, even for planetary imaging. So this will need to be addressed before you upgrade to this size scope.

2.) For visual the SCT will be better than the RC but at that price range a Dob would be a better option imho.

3.) For imaging, with this size scope, the RC is going to be the better scope over all. The SCT will have some major termal problem and all the side problems that come along with that. Along with the price it also weights a lot more because of the front corrector lens(which is the main reason for the price difference). Its a common agreement that once you get to that size scope RCs really start to out pace SCTs. Thats aside from the manufacturer and their respective built quality. One down side, for me personally, of the RCs is that they are usually F/8 compared to F/10 of SCT so you loose a decent chunk of FL, which can add up to a lot if you start tacking on 2x & 4x barlows for planetary imaging. Not so much of a problem if your into DSOs.

[damnut]

Agreed above.

The limiting factors must be the mount & housing. A 16" scope  would require an obsy of some sort. The Meade 16" is a beast !

I remember seeing this a while ago:--

[brantuk]

The RC's usually produce a flatter field and so are preferable for imaging set ups.

[Peter Drew]

I'm fortunate to have two of these, the mount isn't as stable as it looks, You don't want to have to assemble them more than once if you can help it, they are HEAVY. I did take one to Kelling a few years ago. 

[Spacedout]

I think Altair had the 16" RCT at AstroFest and it was quite a beast! Too big for an EQ6 very possibly...

cheers,

Robin

Hello Robin, thank you and yes I should have said I plan to get the EQ8 also.

[Spacedout]

Firstly Im not sure if you are wanting this upgrade for imaging or visual. If you have the budget for this size scope you need to consider several thing, both for imaging and visual.

1.) Your mount is going to be undersized for either scope for visual and massively undersized for imaging, even for planetary imaging. So this will need to be addressed before you upgrade to this size scope.

2.) For visual the SCT will be better than the RC but at that price range a Dob would be a better option imho.

3.) For imaging, with this size scope, the RC is going to be the better scope over all. The SCT will have some major termal problem and all the side problems that come along with that. Along with the price it also weights a lot more because of the front corrector lens(which is the main reason for the price difference). Its a common agreement that once you get to that size scope RCs really start to out pace SCTs. Thats aside from the manufacturer and their respective built quality. One down side, for me personally, of the RCs is that they are usually F/8 compared to F/10 of SCT so you loose a decent chunk of FL, which can add up to a lot if you start tacking on 2x & 4x barlows for planetary imaging. Not so much of a problem if your into DSOs.

Thank you this is the sort of information I want hear as the RC is a much better price size for size.  I plan to get the EQ8 to go with it so hopefully that will make a difference and it will be used with a video camera so visual is not the main priority.  Thanks again for the detailed response much appreciated.  

[Spacedout]

Agreed above.

The limiting factors must be the mount & housing. A 16" scope  would require an obsy of some sort. The Meade 16" is a beast !

I remember seeing this a while ago:--

Thanks Damian, that does put things into perspective I must say!  I do plan to have an obsy at some point for sure in fact it is paramount as my current set up alone is not 5 minute job that's for sure but this video just high-lights the need to make that priority number 1 

[Spacedout]

The RC's usually produce a flatter field and so are preferable for imaging set ups.

Perfect exactly what I want to hear thank you, I was worried I'd get talked out of it 

[Spacedout]

I'm fortunate to have two of these, the mount isn't as stable as it looks, You don't want to have to assemble them more than once if you can help it, they are HEAVY. I did take one to Kelling a few years ago. 

Hello Peter, do you mean two 16" Truss scopes?  What do you mean with the mount?  

[Peter Drew]

Sorry for any confusion, it's two 16"LX200's. One is on the standard Meade fork mount which vibrates a bit if you are heavy handed despite being on an Astro Engineering "Gigawedge", the other is on a professional standard Ealing Beck asymmetrical mount that makes a Paramount look like an EQ1.   

[ollypenrice]

What do you want to do with this big scope? If it is fast frame planetary imaging then I think Damian Peach has provided all the answers anyone would need. SCT.

Flat field is something you need for large sensors used in deep sky imaging. You want to do long exposure DS imaging at these focal lengths? Think very carefully! The EQ8 will not be at all likely to deliver. (I try to avoid EQ8 discussions but an EQ8 as a platform for long exposure at this kind of focal length is something I'm prepared to say might not work. Putting it mildly.)

It really does depend on the intended use.

Olly

[Spacedout]

Sorry for any confusion, it's two 16"LX200's. One is on the standard Meade fork mount which vibrates a bit if you are heavy handed despite being on an Astro Engineering "Gigawedge", the other is on a professional standard Ealing Beck asymmetrical mount that makes a Paramount look like an EQ1.   

No problem Pete but this is what I'm looking at http://www.altairastro.com/altair-rc400-tt-16-truss-tube-ritchey-chretien-astrograph.htmland I hope to put it on an EQ8.  Your setup sounds incredible!  

[Spacedout]

What do you want to do with this big scope? If it is fast frame planetary imaging then I think Damian Peach has provided all the answers anyone would need. SCT.

Flat field is something you need for large sensors used in deep sky imaging. You want to do long exposure DS imaging at these focal lengths? Think very carefully! The EQ8 will not be at all likely to deliver. (I try to avoid EQ8 discussions but an EQ8 as a platform for long exposure at this kind of focal length is something I'm prepared to say might not work. Putting it mildly.)

It really does depend on the intended use.

Olly

Hello Olly, I do not want to do long exposure imaging.  I use video cameras like the Mallincam and such like.  The maximum exposure I normally use is about 28 seconds but more often 7-14 or live of course for planets or Lunar.  I have only ever used my current mount in Alt Az and never really had any issues unless I went over 1 minute or more.  Here is a video I took of M82 at 28 seconds exposure.  

Anyway, my thinking is (rightly or wrongly) that with the larger mirror I may be able to achieve a better view at 28 seconds or the same at 14 seconds or a better live view of Jupiter like this one I recorded in back in April this year. 

 

That said however, I've not done much research into the EQ8 yet.  Is this one to avoid then, even for short exposures?  Perhaps that's another thread 

Many thanks

Karl

[ollypenrice]

That's clear. For your purposes I think the EQ8 should be fine. I think it should be fine for long exposures, too, until the focal length becomes really challenging. I wasn't clear about your intended use. 

Olly

[Peter Drew]

Karl, for your stated purpose I would think that the SCT is certainly worth considering, many top planetary imagers have proved this. I have done a fair bit of integrated image DSO video and the faster the focal length the better, SCT's can operate at F3.3 or lower, the small size of video chips do not benefit from the larger flat field of a RC.

My complete 16" rig on the factory mount cost me 5K 2nd hand.   

[Spacedout]

That's clear. For your purposes I think the EQ8 should be fine. I think it should be fine for long exposures, too, until the focal length becomes really challenging. I wasn't clear about your intended use. 

Olly

Okay thanks Olly that sounds much more promising 

Karl, for your stated purpose I would think that the SCT is certainly worth considering, many top planetary imagers have proved this. I have done a fair bit of integrated image DSO video and the faster the focal length the better, SCT's can operate at F3.3 or lower, the small size of video chips do not benefit from the larger flat field of a RC.

My complete 16" rig on the factory mount cost me 5K 2nd hand. 

Wow what a bargain and does give me something to think about!  I think it will be a case of seeing how long I can wait before such a bargain presents itself.  I spend a lot of time looking on ABS and various other sites for seconds but I've not yet seen a deal that good!   Thanks again Pete I'll report back here once I know exactly which route I'm taking!