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

Started Jun 16, 2014 | Discussions thread
noirdesir Forum Pro • Posts: 13,568
Re: Crop Factor, Low Light and Aperture with m4/3 lenses? Part 2

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?

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

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.

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.

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