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

Started Jun 16, 2014 | Discussions thread
Anders W Forum Pro • Posts: 21,466
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2
1

noirdesir wrote:

Anders W wrote:

noirdesir wrote:

How good that extrapolation is depends on the accuracy of the measurement.

Sure. So what?

Ok, could you predict (without cheating) the resolution of lens A on a higher density sensor if you have the results of lens A and a lens B on a lower density sensor and the results for lens B on the higher density sensor? And what error would you expect?

What I said was that if two lenses perform on a par at 16 MP, then we can predict with pretty good accuracy that they will also do about equally well on at 80 MP. I wouldn't expect much in the way of error, provided that there isn't much in the way of error in the 16 MP figures with which we start out of course.

And there other, indirect aspects, like the chief ray angle which smaller sensors (with the same resolution as larger sensors) are more picky about.

Based on what evidence?

Take the ratio between centre and border resolution of the same lens tested on high and low density sensors. For example on the NEX 7 vs older lower resolution DX cameras, or for the Nikon 1 and Nikon DX.

The NEX 7 sensor is known to have problems with edge/corner sharpness, presumably due to cross-talk. I don't know of any evidence that these problems generalize to other, later 24 MP APS-C sensors or other sensors with about the same pixel density or higher, e.g., current MFT sensors. Note that we now have CX sensors with 20 MP, corresponding to 160 MP on FF, and phone sensors (Nokia 1020) with 41 MP, corresponding to some 600 MP on FF. Still seems to work well, doesn't it?

Take the ISO cheating documented by DxO and Luminous Landscape, the smaller the pixel, the lower the acceptance angle.

Then how do you explain this?

http://www.dpreview.com/forums/thread/3209678

Why wouldn't manufacturing tolerances scale?

Take any CNC machine, their tolerances are very constant over a large range of size of things produced with them. Take balances, once you go below a certain level, the accuracy suffers. Take the process size of semiconductor manufacturing, the waver size does not scale with the process size. Take the pixel density of displays, once you have mastered a certain density, you can produce a wide range of display sizes with it.

The tolerances at issue in this case are those for producing and fitting glass elements. Suppose we were to fit a lens with a diameter of one centimeter and another with a diameter of one meter to the same precision in absolute terms, say one micrometer difference between the edges. Do you think that could be done with the same ease for the one meter lens as for the one centimeter lens?

Already on 10 MP Nikon V1 lenses aren't able to live up to the full sensor potential from f/5.6 onwards which means you couldn't scale down a f/5.6 FF lens and get the same performance.

Why not?

Because by f/5.6 the effect of diffraction becomes large enough to prevent a lens to produce the resolution the V1 sensor could offer ('resolution' being a very loosely defined term here, my observations are based on the MTF50 value). To keep the effect of diffraction constant when scaling a lens design, the wavelength of light would have to be scaled as well.

What I said was 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."

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