Reader Lawrence F writes:
I don't understand how a filter whether colored, UV, or ND would effect the plane of focus on a range finder lens.
My UV and ND filters have never affected my ability to focus with my M9-P. Do the color filters somehow effect resolution?
If so, then wouldn't all camera systems be effected by the same phenomenon?
Wouldn't it be harder to manually focus through a dark filter with live view or through a SLR?
Perhaps a test through colored filters with the D800Eset to B&W jpeg would help answer this question?
DIGLLOYD: As I prove unequivocally with a range of colored filters using the Leica M Monochrom in Filters and Focus Error / Sharpness, there is a shift in focus starting with a faint shift for a yellow filter, and very substantial and disheartening shift with a dark red filter, so much so that f/11 is not adequate to compensate. This is a very serious quality issue that a Leica MM shooter must mitigate when using color filters, or suffer a severe loss of image sharpness.
ND and UV filters pass visible light more or less equally, hence no change in relative focus; one is not attenuating blue and green (e.g., with a red filter); the spectrum is being passed more or less equally and hence the results do not change.
Red/green/blue light all focus slightly differently, slightly meaning 1-2 feet differently at 15 feet of distance even with a well corrected lens! This has been true since the discovery of optics. It is always true, always has been true, always will be true, and unless the lens is a true superachromat like the Coastal Optics 60/4 UV-VIS-IR APO-macro, one must deal with this fact when using color filters with the Leica MM, the Leica APO lenses notwithstanding— they are nowhere near being fully corrected for color aberrations, see Secondary Longitudinal Chromatic Aberration Color Bokeh in Making Sharp Images.