fotografur wrote: James Markus wrote:
I have a medium format crop factor question I am hoping someone can explain to me like I'm a 5th grader. I don't want to get into the determination of crop factors, different aspect ratios, area or hypotenuse measuring, or sensor size. The web is full of incorrect information. I ran into the idea of applying this f-stop crop factor to the lenses maximum aperture. Probably everyone has noticed that medium format lenses have a more narrow DOF wide open, and maybe this was a way to try an explain it? On the Pentax 645Z the crop factor 0.785 - which makes all f2.8 lenses effectively f2.2 on medium format? My brain just can't accept this notion. The manufacturer made the lens for that format and rated it f2.8? It isn't letting more light in than it's rated speed. It only seems to describe an approximation of the 35mm equivalent dof. What am I missing?
I may be reading your question wrong but exposure wise the lens is still an f2.8. I think with the crop factor they are saying the DOF is an f2 equivalent.
Thanks Dennis. That must be it. I simply found another example of inaccurate info. The pre-release video referred to it as "equivalent light gathering ability" - when it was mere referring to DOF.
Jim
Dec 03, 2025 at 07:51 PM
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