FLI Atlas focuser + f.r. for C14 edge

[frolinmod]

As I may have mentioned above, the #94240 0.7x Reducer documentation has an error in one of the diagrams where they show where the back focus is measured from. I posted a diagram excerpted from that documentation above. Celestron support has confirmed that it's in error.

Here are some corrected diagrams:

[djwbne (David)]

Does anyone have experience with locking the main mirror of the EdgeHD 14 in the transport position so that it does not move during a long imaging session and using the Atlas for focusing? I expect that the 146 mm distance from the back plate to the imaging chip would be lowered by the amount that the focal plane moves when the mirror is locked back into the transport position. So, how far is that and would it leave enough room for an adapter between the back plate and the Atlas and provide a flat field across the whole image?

[frolinmod]

With the mirror in the fully retracted and locked position (the shipping and transport position), I don't think you will achieve focus at 146mm back from the baffle lock nut (or reducer). Focus will be at some other position, beats me where though. And if it's not at 146mm back, then it's supposedly not optimal. I've seen the results of it not being optimal and they are grim (egg shaped stars).

The Atlas obviously won't fit on the baffle lock nut without the reducer in place because the knobs are in the way.

I had Precise Parts make me an EdgeHD 14 to Atlas adapter that allows the Atlas to overlap a full 16mm of the thread on the back of the 0.7X focal reducer, thus giving me 16 additional millimeters of space for "stuff" between the reducer and the camera.

Note that I can get a Pyxis 3-inch rotator to squeeze between the knobs so long as I add a 0.2-inch spacer onto the baffle lock nut between the scope and the Pyxis. The spacer is needed because the opening in the 3-inch Pyxis isn't quite deep enough to allow the baffle lock nut to be swallowed to its full height. Then I can add the Atlas after the Pyxis instead of the other way around.

Precise Parts adapters are expensive, so the cost adds up very quickly when you have several made to cover various possible image train arrangements.

[Starblazer99 (Brian)]

I use a moonlight large format focuser on my 14EDGE has the right sized flange and the correct back focus without the need for adaptors 1” drawtube about half way gives 5.75” works fine with the reducer or without, I focus with the scope first then lock the mirror and if needed I fine tune remotely

[djwbne (David)]

I have been advised by the Celestron Technical Support that the 146 mm distance for correct image scale is set in relation to the lens at the rear cell. Therefore, it is not possible to lock the main mirror in the transport position and use an inline focuser to achieve high definition of images to the edge of the field.

[frolinmod]

I wonder at what distance the focus position is when the primary is backed all the way back against the inside rear of the OTA and then locked in place with the bolts. Probably quite close to the rear baffle lock nut.