Celestron Off Axis Guider and imaging setup for C 11 EdgeHD

[brisen (Brian)]

Hi All

Just wondering if anyone has experience with the Celestron OAG on an EdgeHD OTA?

I am looking at purchasing an OAG for use with a QHY 5L II to guide with a DSLR until I can afford a monochrome CCD and filter wheel. Also any advice on a good monochrome CCD and filter wheel for a C 11 EdgeHD OTA would also be greatly appreciated.

Brian

[Rod771 (Rod)]

I was looking at getting one last year for my C11 Edge HD but decided against it for one reason. Celestron over looked one thing in their design of the OAG. The SCT adapter that comes with the OAG has a 2 inch opening/thread, which is perfectly fine when using it in the F10 configuration, it simply screws onto the visual back adapter of the OTA. If however you want to use it with the celestron .7x HD focal reducer, you discover the design flaw.

The reducer is 3.25 inch in diameter with an "exit" lens 60 mm in diameter. So, Celestron have a reducer 1.25 inches bigger than their OAG SCT adapter. I pointed this out and they advised me to remove the visual back adapter off the OTA and screw it to the back of the reducer, then attach the OAG to the adapter. Problem is the visual back adapter has an aperture 37.7mm and screwing it onto the reducer which has a 60mm lens acts as an optical bottle neck creating major vignetting. This was tested in a thread on the Team Celestron website.

The fix - A fellow TeamCelestron member had a custom part made for the OAG which had a 3.25 thread. The only problem with this I noted, was that the custom part cost more than the OAG itself.

The OAG has great features I believe - Helical focuser , rotating prism and camera orientation etc It also maintains 146mm back focus of the Edge HD OTA . Why they cripple it with the narrow bore SCT attachment , I just dont understand.

I've attached some pics of the vignetting and the OAG set up with Celestrons recommendations (on the left) and with the custom part (right)

[brisen (Brian)]

Thanks Rod. I was looking at getting a focal reducer at some point so it is good to know that the two are not compatible as such. I will have to look at other options.

Brian

[Rod771 (Rod)]

I got this OAG click here and followed some of these DIY steps, I only had to grind the slot in the T adapter T2 thread to alow the prism stalk to pass through. The bayonet adapter in my OAG sits inside the OAG body, adding no extra length so I did not have to turn it down on a lathe. Only other thing to get was this M48 to T2 adapter ring.

The OAG replaces the celestron t-ring on the end of the HD T- adapter and is very similar in size (T-ring 10.78 mm OAG 11.18mm) The pick off prism can't be rotated like on the celestron OAG surely making it harder to find a guide star however, the Lodestar camera had no problems.

[Rod771 (Rod)]

Just an update in case anyone comes across this thread.

Celestron have now put a new larger adaptor into production which will allow connection between the HD reducer and the OAG without major vignetting.

This adaptor doesn't fill the whole back focus of 146mm which allow room for other accessories in the image train like filter wheels etc. You will need a 22mm spacer if you are not adding any accessories but please confirm that measurement with Celestron before you purchase or have a part made.

link here

[JMac85X (Josh)]

I have the same issue right now. Like you said, I don't understand why they designed it like that. Do you know the guy that had the CNC adapter made? I'm hoping I could get the specs on it. Celestron is suppose to come out with a new adapter in April but my confidence in them are really low.

[Rod771 (Rod)]

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