distance formula

[john guy]

can anyone please tell me if a formula is known how to set correct distance between a focal reducer and ccd. set up meade 14'' sct and
meade 6.3 focal reducer with atik 383l ccd
any advise much appreciated
regards J G

[Atmos]

Apparently there are two versions of that focal reducer which have two vastly different back focus requirements.

https://stargazerslounge.com/topic/214846-meade-focal-reducer-f63-question/

As for calculations.
BF = Back Focus requirement of focal reducer
FIL = Any filter you may have in the optical path
CCD = The back focus consumed by your camera
Spacer = Spacers required

BF+1/3FIL-CCD= Spacer

I was calculating this morning for a Nikon lens with my setup. I'm using Astrodon filters which are 3mm thick so a third of that is 1mm.

46.5(Nikon Lens)+1(filter)-10(M54 Nikon F-Mount)-4(M54 F Thread)-15(Filter Wheel)-10.5(CCD)= 8mm
This means I need an 8mm spacer to get the desired back focus.