Old 01-12-2012, 02:41 AM
astrognosis (Eric)
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Join Date: May 2012
Location: Essex, England
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Celestron Edge F.R. & system's focal length.

Hi all,

I've finally got my paramount ME and C14 edge up and running in the domed observatory.

I am in the process of doing the itial setting up procedeur. I have a question.

I have the celestron C14 Edge x0.7 focal reducer and I'm trying to get the optimal separation of 146mm between F.R. and chip.

The optical trail is C14 Edge + the focal reducer+ moonlite 2.5" CLS focuser + QSI 532 camera.

What I have been attempting is to set the distance between the f.R. and the camera chip at 146mm and then use the 'scope native focusing knob to obtain as best manual focus as I can. Achieving this I assume sets the optimum. Am I correct in this assumptiom?

Assuming the method above is correct I done this and I have plate solved images using, Astrometric, canopus and Pinpoint and find that the actual focal length of the system is 2800mm ( F:7.87) instead of the 2737mm (F:7.7) it should be for the ideal set up.

I find practice increasing the 146mm separation would allow me to reach this ideal situation How much I would need to increase I'm not sure as I have run out of back focus. But I suspect I'm running away from the ideal set up. I think I have used the correct points in the train to measure the 146 mm i.e on the camera side of the F.R the flat flange that the camera or (in my train the focuser) screws down onto.

Ok I know the chip is small and I can depart somewhat from the ideal, but If I later get a larger chip set up it might be an issue. Besides if it was designed to work this way i'd like to get working that way.

Is my method correct? Any advice on this site would be welcome, I have always found it sound and useful.

Thanks, Eric
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Old 01-12-2012, 03:50 PM
frolinmod's Avatar
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No, not the flat flange. Download an updated manual. The original manual had an error that Celestron have since corrected in the online version. You need to measure from the very back of the reducer (back of the lens housing). The difference is 5/8". See the attachments.

The incorrect reference position is in red, the correct one is black.
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Last edited by frolinmod; 02-12-2012 at 04:00 AM. Reason: spelling
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