Tolerance on Takahashi metal back distance?

[Phil Hart]

hi

I'm getting adaptors made up to connect a QHY9 to my Takahashi Epsilon 160 f3.3.

Takahashi recommend a 'metal back' distance from the thread on the end of the correcting lens tube to the focal plane of the CCD of 56mm.

I can't quite get the adaptors and motor housing on the filter wheel to fit within this distance and will be about 2mm out.

Does anyone know if that is enough to degrade image quality?

cheers
Phil

[leon]

Phil I would say that 2mm is substantial enough to make a difference, however I can't really help with a fix for you, maybe someone else here will pitch in.

Leon

[Phil Hart]

Thanks Leon - you could be just about spot on. I found this thread which quotes a Tak dealer as saying the spec is +/- 2mm:

http://www.iceinspace.com.au/forum/showthread.php?p=381255

I've also been told that the 2.5mm glass filters extend the desired distance by ~1/3 their thickness and I've shaved another 0.5mm off my measurements so I think I'm now as close as I can be given all the uncertainties.

Phil