How to see diffraction in photos

Started 5 months ago | Discussions thread
cba_melbourne
cba_melbourne Veteran Member • Posts: 5,702
Re: How to see diffraction in photos

finnan haddie wrote:

cba_melbourne wrote:

finnan haddie wrote:

cba_melbourne wrote:

finnan haddie wrote:

cba_melbourne wrote:

...

But the effects of diffraction only become apparent in our picture, when the size of the airy disc exceeds the pixel size of our sensor. And that happens the sooner, the smaller the pixel size is.

On a 20 MPix MFT sensor that would mean around f/2.8.

Interesting, is that with the Bayer mask, or without as in a black and white sensor?

For both types of sensors. A Bayer mask just adds funny false colors at the edges.

No, it increases the effective pixel size. Two green, one blue and one red pixel are demosaiced, and result in a larger pixel size for the purpose of diffraction visibility.

Diffraction doesn't care about Bayer masks, as you can easily see in RAW files. Also diffraction doesn't care if you develop your picture in black and white or color of choice.

If you say so...

but I disagree

Maybe this helps: https://www.scantips.com/lights/diffraction.html

What matters is, at which aperture can we start just barely noticing a loss of sharpness on a 20MP sensor camera, when comparing identical pictures taken at various apertures. And I like to claim, that with the 10% very best resolution lenses we have in m43, we just barely can see the diffraction effect taking off at f/5.6. For the remaining 90% of lenses, it is at f/8 or somewhere in between. But hey, your eyes may be better than mine

Another way to explain is this. As long as the airy disc is smaller than the sensor pixel, the lens outresolves the sensor. Only when the airy disc (due to diffraction) becomes larger than the pixel size, can we begin to notice a loss of sharpness.

Not true. In particular with non-circular apertures you'll notice the effects of diffraction way earlier, e.g. sunstars.

Most modern lenses do have near circular apertures.

There are also still modern lenses, e.g. the Voigtländers with straight non-rounded aperture blades.

Sure, but for the purposes of diffraction visibility on a normal picture (not a sunray picture, not a bokeh picture) they are still very much near circular apertures.

But yes, some older repro lenses had indeed square shaped apertures. Beneficial for sharper edges when reproducing texts, or to create half-tone films (before the invention of contact screens in printing).

For $50 you can buy a used Schneider Componar enlarger lens with square aperture. It produces not round, but square bokeh, and 4-ray sunstars:

Or what about the 1964 Ricoh Rikenon lens with triangular aperture? Enjoy the video:

Yup.

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