Quote:
Originally Posted by RobF
I ended up a millimetre or two shorter than what I calculated for theoretical lightpath distance of adaptors etc Troy. I've read somewhere that filters in the light path can "increase" distance. Could be bollox, but seemed to be the case for myself.
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Not "bollox" at all
A typical filter will have an optical thickness about 1/3 less than its physical thickness. The focus shift is T x (n-1)/n where T is the thickness of the filter and n is the refractive index of the glass.
The SX AO unit I just received has an optical length which is 4mm less than the physical distance from front to back. I hope I got the calculations right...
Cheers,
Rick.