Lens__ Circle of confusion

[Alan Klein]

Except with dome ports which produce a virtual image at 4r from the centre of the dome's sphere.

Actually its a wonder that we ever get 'sharp' images with all these complications. I would suggest that photography is, in practice, an essentially empirical activity and (although in my case my original background was in photoscience) we gain experience and as we doo we start to understand many of these and other interactions intuitively because we assess the images produced and learn from them. Digital has speeded this process up.

In generalist photography I am unsure just how much of the science behind image creation is relevant, although it is often interesting and can at times provide an insight into observed phenomena.

Still, what would photforums be without something to discuss and argue about?

Yes dome ports do correct but my Nikonos didn't have one. I shot through the Nikonos lens directly. The other thing is that refraction works through an underwater mask as well. So everything appears 1/3 (25%?) closer to your eyes as well as to the film. The issue is that when you're shooting let's say a 35mm lens, refraction causes the lens to "see" as if it is a 50mm lens due to the refractive magnification.

[Doremus Scudder]

Doremus, in your second paragraph you wrote "Diffusion is always present ..." but obviously meant to write "Diffraction is always present ..." - just for clarity. ...

Corrected. Thanks!

[Doremus Scudder]

Thank you Doremus, at last a serious answer!

Now I have to 'transfer' this as I have the impression that the therms and expressions you quoted can change during translation.
"Confusion", for instance, has so many different equivalents through translation in Flemish/Dutch all having a completely different (contradicting) contents, even in physics, hence my initial question...

phdgent,

I can't help with Flemish, but maybe the German will give you a starting place.

Circle of confusion = Zerstreuungskreis
Airy disc = Airy Scheibchen

Best,

Doremus

[Doremus Scudder]

... For photographic imaging in pictorial situations, the image blur size is a combination of the effect of diffraction, non-ideal optics, and defocus, and the relative importance of these terms depends on the f-stop in use.

Yes, indeed. There's a sweet spot between DoF and diffraction effects that I always seem to be trying to hit. Final print size (and viewing distance) make a big difference here too. I won't hesitate to use f/45 (on 4x5) when needed, but then try to keep print size down to 11x14" or smaller.

Best,

Doremus

[xkaes]

Yes, indeed. I won't hesitate to use f/45 (on 4x5) when needed...

Best,

Doremus

For me, f22 is just a number, not a wall. There are times when I need to climb over it. And since I like macro work, f16 can become f45 very easily.

[Drew Wiley]

Depends on the size of your enlargements. Diffraction starts visibly kicking in with 4x5 by 20X24 print size when viewing close-up, or possibly even in a 16X20 print. I try not to go past f/32 with 4X5, or f/64 with 8x10.

[xkaes]

I try not to get very close to my very large prints. With a little practice, it's quite easy.

[Drew Wiley]

People get nose up to mine. I strategize them that way - the push/pull of distance. I want the general composition to be compelling from further away, yet to draw the viewer in to explore the detail over and over again, and keep discovering new things, not only in detail, but actual composition. If I can enjoy a big print on my own walls for decades, then I consider it a success. But when I need a break into my alter-ego, I pick up the Nikon and some grainy film and make poetic little prints which might not be truly sharp at any level.