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

Started 6 months ago | Discussions thread
Anders W
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Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
In reply to bobn2, 6 months ago

bobn2 wrote:

Anders W wrote:

bobn2 wrote:

Anders W wrote:

Just another Canon shooter wrote:

Anders W wrote:

Just another Canon shooter wrote:

Anders W wrote:

"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."

There is no such thing as limited by lens aberrations only.

In optical theory there is.

No, there is not.

Yes there is.

Anders, please cite this 'optical theory'. So far as I know, there is always diffraction. How is any lens not subject to diffraction?

There is always photon noise and read noise. Does that prevent us from isolating their effect on image quality?

Change the topic, why don't you?

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.

You say that in optical theory there is a lens limited by lens aberrations only. No, there isn't. You might say that in some circumstances the effects of diffraction are small enough to be ignored, but that is a matter of analytical practice, not theory.

I think you just like arguing, Anders, because you could have quite easily clarified your meaning to JACS and stopped there, instead of insisting that your obviously incorrect statement was correct.

You might remember this paper by Cossairt et al. On p. 3 they express the same thought that I expressed above.

"In conventional lens design, resolution is limited by the spot size of the lens. For a lens with aberrations, spot size increases linearly with the scale of the lens."

Would you say Cossairt et al. speak about the impact of aberrations only in the passage I quote or are they talking about the joint impact of aberrations and diffraction?

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