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
1

Just another Canon shooter wrote:

Anders W wrote:

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."

This is trivially true because it is a statement about a non-existing situation. Similarly to the statement: "All 100-leg cows can fly".

You got that wrong. The implication is that two lenses of the kind I describe would for all practical purposes be equally good wide open and a few stops down, since the impact of lens aberrations at those apertures is large and that of diffraction trifling. This in turn explains why results like those I showed you earlier (Panasonic 20/1.7 being roughly on a par with Leica M Summilux 50/1.4) are to be expected.

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.

At equivalent stops, the smaller format lens can NOT be a scaled down version version of the larger one.

Of course it can. For example, the MFT 25/1.8 at f/1.8 would be equivalent to the FF 50/1.8 from which it was scaled down at f/3.6.

This is the relevant question, actually.

I didn't see any question.

Here is a 100% crop of a shot I took yesterday, 135/2 on the 5D2. The guy was not staying still, of course. Default sharpening in LR.

And here is his pin, I did not even remove the CA:

Which of your f/1 lenses can do this?

As I already informed you, I don't use f/1 lenses. My 75/1.8 works nicely in cases like these. The samples below are available at full size for those who want to check them out.

 Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus OM-D E-M5 Olympus E-M1 Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +28 more
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