PL mount adapter with ND filter

How do you account for the change in backfocus, particularly in the version that you sell as an upgrade to people with current units?
 
Mitch Gross said:
How do you account for the change in backfocus, particularly in the version that you sell as an upgrade to people with current units?
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The thickness of the E-mount ring is still the same. If the backfocus was correctly adjusted via shims , replacing rings will not change the FFD distance.
 
ciecio7 said:
The thickness of the E-mount ring is still the same. If the backfocus was correctly adjusted via shims , replacing rings will not change the FFD distance.
Click to expand...
Sorry, but that's not how it works. When you place a piece of glass behind the lens the refraction of light changes the backfocus by about 1/3 the thickness of the filter. That may not seem like much but it is certainly enough to make it impossible to focus wider angle lenses to infinity. This is why lenses with rear filter holders generally ship from the manufacturer with a clear filter in place. The lens is calibrated based on the inclusion of a glass filter at that point in the optical path. Your lens mount adapter is no different so it should be set with a clear filter in place when ND or other filtration is not in use. That is the proper way to maintain backfocus. Flange Focal Distance cannot simply be measured by the mechanical distance. When you introduce optics they must be accounted for as well.
 
I'm pretty sure it works the other way- you'll pass infinity. But your focus marks will be off and you may not reach the close focus. And it its roughly 1/3 glass thickness- Mitch is absolutely correct here
 
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