Quote:
Originally Posted by Merlin66
The answer is the 44mm stated in text.
|
I know I'm getting down into the minutia here Ken but I'm going to argue that the answer is not as definitive as that. Yes, the set back distance is 44.0mm for a Canon EOS lens when installed on a Canon DSLR body. However, if my calculations are correct, the set back distance I should be using when I connect the lens to a CCD or CMOS camera should be 43.67mm. I realise that I'm only talking about .33 of a millimeter but it can, and will, make a difference.
Specifically as it relates to the components in my image train, we have the following:
ZWO ASI6200. The sensor is set back 12.5mm
ZWO 2" EFW = 20.0mm
Astronomik 50mm filters - optical thickness = 0.33mm
(The Astronomik filters have a glass thickness of 1mm for an optical thickness of 0.33).
If I take the target set back distance to be 43.67mm for the Canon EOS lens, then to calculate the adapter length I have:
43.67-((12.5+20.00)-.33) = 11.5mm.
If I were to use the 44.0mm figure as my target set back distance then I would get an adapter size of 11.83mm. Not much but can make a difference.