AA filter question - Joe?

Started Feb 9, 2012 | Discussions thread
Joseph S Wisniewski Forum Pro • Posts: 34,130
The resolution limit is way out there...

Richard Frederick wrote:

Looking at both the Sony NEX-7 and and Nikon D800 pixel density, it seems to me that the sensors can now out-resolve most of the lenses used with them. Does this not remove the requirement for AA filters? Apparently not, otherwise the cameras would not be so equipped (D800E excepted).

Can anyone bring me up to speed here? Joe?

I did some calculations on this a while back (and bear in mind that I'm sick as a dog right now and my memory is nowhere near 100%, but I think this is about right) and based on the Rayleigh criterion (the size of the Airy disc, the measure of diffraction) a "perfect" f1.4 lens will resolve about 1.2 microns.

Considering the green-to-green pixel spacing of a Bayer filter sensor, that's 1.2 gigapixels on a FF camera.

But I think the practical limit is closer to 400mp on FF, and about 200mp on APS. At that point, you simply won't be able to stabilize or focus a camera well enough in general photography to get aliasing, the "system" will have enough blur to do it.

And, as the pixel pitches get tighter, it gets more and more practical to imagine moving the sensor in a small, square pattern to do the AA, instead of using liNbO3 slabs, so I'm betting the day of the AA filter you can switch off is drawing near. Picture a 60mp camera knowing that f8 has enough diffraction for complete anti-aliasing, f5.6 needs an additional 0.4 micron movement, f4 needs 0.7, on up to 3.3 at f1.4.

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Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph


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