Diffraction and ultimate FF pixel count

Started Jul 31, 2019 | Discussions thread
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JimKasson Forum Pro • Posts: 39,791
Diffraction and ultimate FF pixel count

The announcement of the 61 MP a7RIV has reignited the oft-heard arguments that photographers don't need any more resolution in their cameras than they have now. There is a variation on this argument that says that a reason why greater resolution brings no benefits is diffraction.

It is undeniably true that there are pixel pitches and apertures beyond which diffraction will limit resolution. A relevant question is: "What pitches and what apertures?"

I constructed a spreadsheet to answer that question.

I assumed 555 nm (green, mid-visible spectrum) light, and computed the Sparrow distance, the place where the sum of two Airy disks develops a flat top. Then I calculated the number of Sparrow distances that would span a FF sensor horizontally and vertically. I multiplied those two together to get how many MP a FF sensor would have to have to sample a diffraction-limited lens at the Sparrow distance. That's the column labeled "MP".

Finally, to get adequate sampling of the diffraction-limited image by the red and blue pixels of a Bayer color filter array camera, I created the far-right column.

Consumer diffraction-limited lenses are thin on the ground, but these numbers serve as  an indication of the physical limits, absent techniques such as are used in making semiconductors and in microscopy.


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