Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Started Jun 16, 2014 | Discussions thread
Anders W Forum Pro • Posts: 21,468
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

Just another Canon shooter wrote:

Anders W wrote:

I hoped you might see the analogy, but apparently I was mistaken. So let me translate: The fact that certain factors are always present does not prevent us from isolating their impact.

The part that you keep ignoring, is that their (diffraction) impact is different for the two cases we discuss.

After a lot of dancing, you are trying to change your statement to something like this: If we can perfectly scale a lens and consider the geometric optics theory only, the projected images scale by the same factor, as well. Duh! Do you really think that we are still discussing whether if you can shrink something, it shrinks?

What I originally said in my first reply to noirdesir is the following:

"What is known based on the laws of optics is that if we take a lens design for a certain format, say a 50/1.8 for FF, and scale it down in all relevant dimensions so as to make 25/1.8 for MFT, the two lenses will deliver the same resolution if we measure per image diagonal (and the MFT lens twice as much as the FF lens if we measure per mm) at the same f-stop as long as resolution is limited by lens aberrations only."

I haven't changed that statement, just substantiated it (see my reply to bobn2 here). And the implication is that the larger sensor has no advantage as far as optical aberrations are concerned. In view of the discussion in this thread, that's hardly a trivial claim.

As to diffraction, the larger format has an advantage when comparing at the same (rather than equivalent) f-stops. At equivalent f-stops, there is no difference at all, and the impact of diffraction is generally trifling at wide apertures.

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