Diffraction. When does it really matter with LF?

[Bernice Loui]

High contrast images often gives the visual impression of "sharper" when the perceived sharpness is not real. This has been discussed many times previously on LFF.

One of the advantages that comes from larger sized sheet film is the ability to hold subtle contrast renditions that can be difficult to impossible on smaller film formats.. this has ZERO to do with image sharpness or resolution. It is why soft focus lenses used on 8x10 film and larger then contact printed have rather special image qualities that cannot be achieved any other way.

Possible image resolution aka "sharpness" with smaller film format is difficult to achieve making this a goal to achieve? While sheet film often gains image resolution by brute-force film recording area rendering the many other aspects of print image quality far more significant than simple sharpness.. which could be a residual obsession from those beginning LF endeavoring into LF sheet film?

Diffraction effects can be reduced by limiting the light used to create the image to a shorter wave length, as in blue light can theoretically produce a higher resolution image than red light with the same lens aperture. Much a matter of smaller can fit more in then out of a fixed sized area.



Bernice

[Ulophot]

At the risk of redundancy, I'll sing my note about portraiture, as an illustration of principle.

Others have noted that the final result, or look, you desire to achieve, is determining. Not every portraitist desires tack-sharp images or will print poster-size, and I am one. I don't really want a super-apochromat ultra-sharp lens for my work (though I admit to having been through my share of if-only-I-had syndrome), and frankly, my 210 Komura and 135 Nikkor (which latter some have called the dog of the line) leave me nothing to complain of. Though I have come to LF for the essentially invisible grain among other features, I shoot fast film in both 4x5 and 645. At 11x14, even with cropping, if I have done my job well, the content of the image will convey itself past all but those who really aren't looking at the portrait but at the rendering of insignificant detail. I have done it myself, so I make no judgement, but like to remember Adams's dictum, variously stated, that nothing is more pointless than a sharp image of a fuzzy concept.

I had posted a question similar to yours in the forum a while back and got some good advice about diffraction and sharpness-optimization at various distances with my lenses. I made some tests. For my work, the issue is now behind me, as for a number of others posting here. (You might take a look at Doremus's beautiful work on his website, among many others.)

[Mark Sawyer]

Well, it can't be corrected.

Diffraction can be corrected by opening up the aperture. Just like you can correct spherical aberration or curved field by closing down the aperture.

But one can also correct spherical aberration or curved field by altering lens design, which doesn't work for diffraction. So maybe.

Just curious...

[Drew Wiley]

That's not correcting diffraction, just reducing or avoiding it. If you need a small aperture, you need a small aperture, and diffraction comes with the territory.

[Mark Sawyer]

Agreed, Drew, but which other aberrations are ever corrected to perfection, not just reduced or avoided?

[Drew Wiley]

For all practical purposes, most modern large format lenses are very well corrected relative to typical applications. It's a tougher climb trying to squeeze the same amount blood out of tiny cherry tomatoes. I feel the pinch whenever I mix MF prints into the same portfolios as LF prints; and that's where being nitpicky about lenses really counts.
I've seen sample photos from classified cameras that were almost unbelievably well-corrected; but even if I could afford a hundred thousand dollar lens and a two hundred pound camera, it wouldn't improve my own work one bit. The most important lens set ever made is your own pair of eyes.

[Bernice Loui]

The most important item in the print making process is the Artist-Photographer. All that ~hardware~ stuff are mere tools as a means to accomplish an Artistic expression via images.

A very crude and not the best analogy for diffraction would be the volume of beans that can be passed in then out of a fixed dimension opening with the volume of beans used to create an image. If the dimension of the opening these beans are going in then out of is reduced, the volume of beans used to create an image is reduced. At some point if the opening is made smaller than the individual bean, the flow of beans stops or no image can be created with the beans.


Bernice

[Mark Sawyer]

A very crude and not the best analogy for diffraction would be the volume of beans that can be passed in then out of a fixed dimension opening with the volume of beans used to create an image. If the dimension of the opening these beans are going in then out of is reduced, the volume of beans used to create an image is reduced. At some point if the opening is made smaller than the individual bean, the flow of beans stops or no image can be created with the beans.

In our case, that would be an opening in the photon-wave-amplitude size, something well below f/64 for our lenses.

One thing I don't understand about diffraction is why it is affected by focal length. It seems that it should be an effect of photon ray and raw aperture size. This is me not getting it, but why would diffraction be more on a 1000mm lens at f/100 than on a 100mm lens at f/10? Disregarding the power of the front element, they'd both have the same aperture size. I tried to figure it out from the Fraunhofer diffraction equation variations, but it just made my head hurt...

[Dan Fromm]

But it isn't affected by focal length. Effective aperture, a dimensionless number, is what matters.

[Vaughn]

The most important item in the print making process is the Artist-Photographer. All that ~hardware~ stuff are mere tools as a means to accomplish an Artistic expression via images...Bernice

And the tools shape the artist as well as the art.

The rest of you post reminds me of the joke about the racket all the different body parts were making, arguing about who was the most important -- finally the small sphincter muscle quietly said "Quiet up there, or I'll clamp shut for a week." And peace prevailed again...