Couple of questions - Sony a6000

Started Mar 14, 2014 | Discussions thread
Euell Senior Member • Posts: 2,485
Re: Couple of questions - Sony a6000

mrbenji wrote:

Euell wrote:

Is that accurate? I believe that diffraction is not dependent on the resolution of the sensor, but rather on the physical size of the sensor (e.g., APSC, full frame, etc.). Increasing the resolution of the same size sensor should not increase diffraction at the same F stop.

Well, the size of the diffraction effect (a.k.a. the "airy disc") at a given F stop is always the same size regardless of the sensor's resolution, but the sensor size ALSO doesn't affect the "airy disc's" size.

Sensor size AND resolution are relevant, though, because diffraction doesn't negatively affect resolution until the "airy disc" is larger than a single pixel -- on a higher resolution sensor of the same size the individual pixels are smaller, so the effects of diffraction will be visible earlier. *This,* and not the actual sensor size, is why, for instance, a 24MP APS-C sensor will begin to experience the effects of diffraction earlier than a 24MP FF sensor will... what matters is the size of the pixels, not the size of the sensor.

The size of the "airy disc" is larger than the pixels on 16MP APS-C sensor by about f11, but it exceeds the size of the smaller pixels on a 24MP APS-C sensor by about f8.

The easiest-to-understand description I've found so far is this one:

Anyway, the fact the "airy disc" is always the same size at a given f-stop is why I said I can't fathom how a higher resolution sensor's "effective resolution" could ever be worse on a lower resolution sensor than a higher-resolution's "effective resolution" at the same f-stop. I wouldn't be surprised, however, if at very small apertures their effective resolutions began to converge.

I don't disagree with you, just your terminology. The effects of diffraction indeed may vary dependent upon pixel density, but that is a phenomenon other than diffraction.

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