GSO RC8 v GSO RC10

I hope you can get answers, i will watch this topic, because i bought TS Optics 10" RC in truss design, found one brand new with nice offer, a truss design is better, also this one of 10" has primary mirror decoupled from the focuser so collimation could be easier then, but i don't have a full frame camera nor corrector, and not sure if i should use it at native FL or reduced, there are few reducers such as 0.8x r 0.75x and the popular one 0.67x but it is not good for a full frame.

I only have AZ-EQ6 mount, i asked about it also, some said it is possible with more counterweights, and some said it is limited, or can be done but not good enough, can't guide well or only short exposures, whatever it is my scope is still in the shipping box since last year i received it, we will see what people will say about 10" RC and EQ6 mounts.

I sometimes image with my 10” TPO truss RC. While I can’t directly compare it with a your 8” RC, it is quite the light bucket and is capable of creating images that are as good as my AP skills allow. I have a few of them posted but, since getting my TEC 140 setup on a permanent pier, I don’t really image much with the RC. I’ll often set it up for visual while the TEC is imaging and it makes a great visual scope. 

As for your mount question, one thing I’ve liked about the truss OTA is that it keeps the weight very centralized. The center of gravity, depending on the optical train, tends to be in line with or very close to the plane of the primary mirror. Payload on most mounts is not a static number but depends on both the weight of the payload and how far it extends. This scope keeps it close to the declination axis, which should help the mount handle it closer to its upper limits. The truss design also catches less wind, which helps on a breezy night. 

I’ve used mine with a 10Micron  GM1000HPS with a stated capacity of 25kg and a full payload including filter wheel, OAG, guide camera, dew controller, power box, feather touch 3” focuser, corrector and large cameras (QHY268 and ATIK16200 - not at the same time). It has tracked well for long exposures. I know it’s comparing two very different mounts but hopefully it’s a helpful reference point. 

FWIW, while I’ve been impressed with this scope for its price point, I am planning to do a second permanent pier with a larger reflector and plan to upgrade to a higher quality OTA, like a 12” CDK. So while I like the RC a lot I don’t plan to build my permanent install around it. In fact, I plan to sell it. If you decide to go that route, let me know if you’re interested in a second hand one at well below retail. I can sell it with the original focuser or the feathertouch.

Btw, your posted images on your 8” are really impressive and way better than any I’ve made with my 10” (although I’m sure that has far more to do with skill of the user than any difference in aperture).

Very kind of you to say so - but I expect it also has a lot to do with a very dark site!

Rod Kennedy:
Hi Brian

1) Yes: I have both scopes GSO Carbon RC8 and GSO RC10 Truss.  The RC10 is noticeable superior.  If you have an ASI6200 then the relative expense is low.

With the standard AP CDCT67 compressor (and tweaked spacing) my setup ends up running at 1426mm focal length.  I think the image circle would be smaller than the ASI6200 (43mm diagonal), because it would be 30mm.  I use a ASI294MM (23mm diagonal).

If I were you, I would use the flattener (image circle 45mm) and bin 2x2; you would have 0.78 arcsec/binned-pixel, which is perfect.  People get hung-up about focal length but it is the combination with pixel size that counts.

2) No: I also have an EQ6-R mount which I use on the RC8.  I think the RC10 is too big for this mount.  I have a bigger mount for the RC10.  I never even tried it.  My experience with another combination where I was at the mount limit proved poor for astrophotography (too much rotational inertia for the mount to easily handle).  It would still work fine on still nights though.

Cheers Rod

Hi Rod,

A very comprehensive and helpful reply.  Thank you.  I also have the CDCT67 compressor and the image circle is just a little too small for a full-frame sensor.  I agree than binning is a very sensible option.  Although I do like a lot of pixels, even a 2x2 binned ASI6200M is a 15M pix image - more than enough for most purposes [although a CDCT67 reduced fov would start to hurt!]

What mount do you use for your RC10?  Again this will add to the cost, as it appears to be a big leap up from the EQ6 to the EQ8.  And, I suspect I will have to engage. in fabricating another mount converter as I doubt the footprints of the mount will be the same.

CS Brian

Hey Brian, here are my responses to your questions:

1. I would say it would be worth the cost considering the RC8 isn't well suited for a sensor as large as the 6200 IMO. The RC10 will be much more capable of handling a full-frame sensor (with a field flattener of course). However, I would still be in favor of imaging at 2000mm rather than 1600mm, but each to their own.

2. The EQ6-R should just about be able to handle the scope, provided you balance carefully. I speak from experience on this one as I used to use my EQ6-R to carry my RC 10 scope. I have however since switched to using a heavier EQ8 for good margin.

Hope this helps.

Rod Kennedy:
Hi Brian

1) Yes: I have both scopes GSO Carbon RC8 and GSO RC10 Truss.  The RC10 is noticeable superior.  If you have an ASI6200 then the relative expense is low.

With the standard AP CDCT67 compressor (and tweaked spacing) my setup ends up running at 1426mm focal length.  I think the image circle would be smaller than the ASI6200 (43mm diagonal), because it would be 30mm.  I use a ASI294MM (23mm diagonal).

If I were you, I would use the flattener (image circle 45mm) and bin 2x2; you would have 0.78 arcsec/binned-pixel, which is perfect.  People get hung-up about focal length but it is the combination with pixel size that counts.

2) No: I also have an EQ6-R mount which I use on the RC8.  I think the RC10 is too big for this mount.  I have a bigger mount for the RC10.  I never even tried it.  My experience with another combination where I was at the mount limit proved poor for astrophotography (too much rotational inertia for the mount to easily handle).  It would still work fine on still nights though.

Cheers Rod

I've heard that binning a CMOS camera is kind of pointless as it doesn't work in the same way as a CCD camera does. I image at bin 1x1 with an IMX 571 camera, which gives an image scale of .39"/px. It is oversampled, but this isn't an issue for me as I only image and accept subframes that are taken from nights with good to excellent conditions. You can always downsample in post-processing.

The EQ6-R is just about able to handle the RC 10 with a full image train, though I also switched to using an EQ8 to have a greater margin of capacity (if that was a term )

Thanks so much PE.  Yes its certainly true that you dont gain as much from binning a CMOS as a CCD - since the read noise is not reduced.  I bin only at the post-processing stage.  

Interesting to hear of your experience with the mount.

CS Brian

Rafał Szwejkowski:
I went 6 - 8 - 10.  Each was noticeably superior to the smaller version.

1) absolutely yes, it basically lets you do 1400-1600mm with reducer at about f/6 which is the same as 8" without reducer at 1600mm - f/8.  That's almost twice the SNR per exposure.  I recommend a reducer unless you just want to shoot lone galaxies and PN.

2) yes for non-truss, but it's probably close to the limit of this mount.  Truss is heavier and would probably be not comfortable for the mount, although doable with some loss of accuracy to be expected.

Truss is slightly lighter than the non-truss model, and even with the gear I put on, the scope managed just fine under good conditions. Under excellent conditions, guiding was as low as .32" RMS.

Rafał Szwejkowski:

Rafał Szwejkowski:
I went 6 - 8 - 10.  Each was noticeably superior to the smaller version.

1) absolutely yes, it basically lets you do 1400-1600mm with reducer at about f/6 which is the same as 8" without reducer at 1600mm - f/8.  That's almost twice the SNR per exposure.  I recommend a reducer unless you just want to shoot lone galaxies and PN.

2) yes for non-truss, but it's probably close to the limit of this mount.  Truss is heavier and would probably be not comfortable for the mount, although doable with some loss of accuracy to be expected.

Truss is slightly lighter than the non-truss model, and even with the gear I put on, the scope managed just fine under good conditions. Under excellent conditions, guiding was as low as .32" RMS.

I was going by the information provided by the manufacturer, did you have an opportunity to weigh them yourself?

Intrigued, I looked up the specs and what you said holds true. However, when I compared to the specs given by Orion (a brand that sells GSO RC scopes), it indicates the other way around. The weight difference is minimal regardless.

Brian Boyle:
Thanks to everyone who replied to my post - really very much appreciated.

In summary,

1) Does it make a difference? Yes - and better suited to a FF camera. [Larger focusser, so less vignetting?]
2) Will I need a new mount? Maybe. But try out it with the EQ6R-pro first. 
3) 1600mm focal length a little long [but resampling in post-processing a good option]

Many thanks, everyone.

I use a RC10 with a 8lb 3.5" Nitecrawler focuser on it with my EQ6R and my guiding is great. I'm using 44lbs of counterweights and 44lbs of scope. Best guiding is .25" but average is .4"

Matthew Proulx:
I use a RC10 with a 8lb 3.5" Nitecrawler focuser on it with my EQ6R and my guiding is great. I'm using 44lbs of counterweights and 44lbs of scope. Best guiding is .25" but average is .4"

What happened to your RC 12? I have a similar experience with my RC 10 as well on my EQ6-R before switching to the EQ8.

Thanks for all the advice.  Going for the RC10 with 0.8x corrector/reducer [plus dew shield, extra baffle and "truss sock"]. Will keep my EQ6-R for the time being...

CS Brian