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C6 SCT Barlow setup and general backfocus


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Tried imaging mars last night via my c6, but for some reason could not get the camera to see anything in the field of view at all.

Tried via a 2 inch visual back and a vixen flip mirror, the camera being on the straight through part and it couldn't see anything when flipping the mirror despite the visual eyepiece showing correct focus. Tried removing the straight though extension piece and screwing the camera direct to the prism box, nothing. Connected the camera to a variable extending t nose extension, again nothing. Tried with just a plain diagonal, again nothing. The 224mc was working because when I took it out it was showing the light from the environment. Focus was racked from one extreme to the other in all examples.

I'm querying this because the first time I did it I managed to image Jupiter with straight through extensions making up the approx 105mm backfocus distance, but it didn't work this time. Eventually I'm going to want to introduce a 2x Barlow but until this is sorted I don't think I should try to complicate things further with the Barlow.

Edited by Elp
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  • Elp changed the title to C6 SCT Barlow setup and general backfocus

I have used a similar setup, and I was able to flip between the ASI224MC (in focus) and 25mm eyepiece (roughly in focus) with the camera screwed directly to the mirror box via the T-thread adaptor.

TBH I have never bothered my head about "back focus". 

Unless the camera is a) in focus and b) accurately aimed at Jupiter, i.e dead center* in the eyepiece, you won't pick up a thing.   The camera field is much smaller than the eyepiece field even if you select the full chip as the ROI.

I suggest dispensing with the flip mirror as you should not need it for locating in-your-face bright objects like Jupiter.

* or maybe offset by a small amount depending on the mirror setup.

Edited by Cosmic Geoff
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That's what I was thinking, but was surprised not even a star was in view despite the 1500mm focal length. Makes me wonder how much more difficult it will be with a Barlow at 3000mm. Next time I'll also have it on a motorised mount.

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