What image train diameter for Edge HD 1100?

[gorann]

I just bought a Celestron Edge HD 1100 (and the EdgeHD x0.7 reducer) and realize that T2 will be too narrow to use for the image train. It may be fine with my APS-C Canon and Atik 460, but I am quite sure T2 would be causing vignetting if I get a larger chip camera (I am tempted to get something like Canon 5D or 6D, or a Sony a7s one day). The image circle at the focal plane of this scope is 42 mm and I expect the light path to be wider closer to the SC ring (the opening on the reducer is 60 mm). I am thinking about using a 2" / M48 system connected to the scope/reducer with the big-SC to 2" Baader adapter:

http://www.teleskop-express.de/shop/product_info.php/info/p2430_Baader-2--Click-Lock-eyepiece-and-adapter-holder-for-the-big-SC-thread.html

Then I would find the proper 2" spacers (ideally the focal plane should be 146 mm behind the SC thread) and finally connect to the DSLR with a M48 - Canon adapter rather than T2 ring (Teleskop-Service sells an M48 adapter).

Maybe I even need to go for M68, but that would bring up the price and reduce the number of filter holders and OAGs I can use.

Celestron do not give much advice in their manuals or white paper, even if the EdgeHD series is aimed at imaging. In fact, the only option sold by Celestron (a big SC adapter with the right spacing) ends with a T2 thread that is smaller than the 42 mm image circle.

So, can anyone with experience of these large Celestron SCTs tell me what to go for, and what they use?

[Jessun]

Hi Göran,

Go for M68 I'd say. You can always add a slim M48 step down ring at the camera/filter end.

You'll get future proof flexibility and a rigid system. TS have a great M68 rotator that I use, and it's even easy to fit a separate 2" filter inside the M68s just in front of the filter wheel. (Let's say a LP filter ahead of LRGBs).

Here's the rotator (well, one part of it)

http://www.teleskop-express.de/shop/product_info.php/info/p6443_Baader-M68-Wechsler-mit-M68-Aussengewinde---2458180.html

/Jesper

 

[gorann]

Thanks for the info Jesper!

I see the point about stability with M68 but would 2" be enough to avoid vignetting?

[Jessun]

Best answered by members with knowledge about this scope and reducer setup Göran. My guess would be that it shouldn't cause additional vignetting given that the reducer is in the imaging train.

I hope others come in on this for you who have been through the same thoughts.

/Jesper

[pyrasanth]

Sorry I came late to the party I've been away in real life. I quote from a Cloudynight forum post "but for the C11 Edge, at f10, it says it's fully illuminated in a 16mm circle, and falls off gradually to 83% out to 42mm."

So- as I always suspected Celestron are somewhat liberal with the truth about there Edge specifications. I have no problems with the Atik 460 being fully illuminated at any focal lengths but I suspect the KAI 11002 on the Edge 11 at 0.7 will hit problems as the chip is 37.25 x 25.7 which may well illuminate at F10 but at F7 I would expect significant vignettig making its use problematic. This is proven with the RASA which has the same size imaging circle at 42 mm & the vignetting is quite horrible. I think it would work better with a DSLR on the RASA as your coupling more directly to the OTA & not taking the intermediate step of an additional thread holder at M42/M54 to carry an LRGB filter choice in the imaging train which again presents its own problem. I think the Edge optics are great for smaller CCD's like the ATik 460's but I'm convinced that I need a true Astrograph for KAI 11002 & above size CCD's.

I'm about to order the ONAG XM which is the full frame version of the ONAG that I used to take the M101 picture. This will give me a far greater idea as to what issues are faced with the larger chips. I will carry out some tests and see what I come up with using the ATik 11000.

The adapters that couple the standard ONAG are M42 & they work fine with the Atik 460. The adapters for the XM will all be M54 at the camera (thread & filter holders). There is no point in going larger as the restriction is going to be at the Atik 11000 coupling which is M54.

[gorann]

Thank you both!

Right now I am thinking about getting Celestron's OAG and attach it to the big-SCT port at the end of the EdgeHD1100. I have been reading up on it, and it is an interesting story. Apparently it is a great OAG sold with adapters that put the camera at the perfect distance (146 mm) but Celestron initially messed up by having a narrow small SCT connection to the telescope causing vignetting (especially when using their 0.7 reducer), defeating the whole purpose of using it with the largish image circles of their large SCTs, especially with their expensive and massive 0.7 reducers with 60 mm opening, see:

http://www.iceinspace.com.au/forum/showthread.php?t=115993

Fortunately Celestron listened and made a big-SCT adapter for it (sold separately), but unfortunately messed up again since the adapter makes the image train shorter than the original and finding the right spacer will be tricky (I think it could be done with a 22mm M48, which unfortunately is not standard). This is the customer review on the Oceanside Photo and Telescope site:

"This well made adapter widens the input end of Celestrons OAG, reducing vignetting on full-frame cameras. Regrettably, the OAG part it replaces is 0.86" longer. The spacing on C11 Edge scopes is critical, and has to be within 0.5 mm. None of the spacers in the existing OAG kit work to achieve the needed additional 0.86" for the C11. This might be made to work for an 8" scope, or some non-Edge scope, or possibly a non-full frame camera, though that would negate the point of having it. It in essence needs a 0.86" extension with 3.29x16 tpi threads at either end."

Fortunately, I think he may be wrong in saying that a 0.86" (=22 mm) extension with 3.29x16 tpi is needed (presumably he mean on the telescope side). Such a thing would have to be custom made and probably cost more that the OAG. I think it could work with M48 on the camera side and a T2 spacer for the guide camera. I am waiting for a reply from Celestron USA about the issue......

[ollypenrice]

On 26/5/2016 at 12:16, pyrasanth said:

 

So- as I always suspected Celestron are somewhat liberal with the truth about there Edge specifications. 

Liberal with their falsehoods might be more accurate? And parsimonious with the truth?

Olly