selmslie Loc: Fernandina Beach, FL, USA

It's not indirect if you can plug it onto a formula.

The calculations show that if the Maximum Circle of Confusion is less than the Diameter of the Airy Disk it is arbitrarily Diffraction Limited.

Like most things you can calculate in photography, the mathematical result is more precise than anything you can actually see.

The problem with their diffraction limit calculator is that they only incorporate the maximum print dimension and the viewing distance (like they do in their DOF calculator) for film. That changes the value of the CoC which in turn affects the diffraction limit. With the CoC based on pixels the CoC calculation is based on a 10 inch print and the default 25cm viewing distance.

imagemeister Loc: mid east Florida

Yes, I SEE ....

larryepage Loc: North Texas area

Hi Urnst. I've been watching this discussion. A lot of what has been said is mostly true, but a couple of errors persist, and the discussion does not explain the reality of what is going on, nor does it explain how to understand why it matters.

It is important to understand that diffraction is a phenomenon caused by edges in an optical system. All lenses have edges bounding the images. Most of the time, this edge is the edge of the iris blades. The only exception usually occurs when the aperture is fully open.

So we have these diffraction effects, which are confined to the area near the "edge" that creates them. At wide apertures, a very high percentage of the image is formed by light that has not passed through the diffraction zone. As the lens is stopped down, the proportion of light that passed through the distortion zone grows. At tiny apertures, the proportion of light which has been affected is highest.

Is this proportion enough to make a visible difference? Maybe, maybe not. Depends on how small that aperture is. Depends on whether the lens is intrinsically good enough for the effect to make anoticeable difference. Depends on whether the skill and technique of the photographer is good enough not to introduce even bigger problems. Depends on whether the lens elements are clean enough that they are not introducing even bigger problems. May depend on a lot of other things, as well.

In my experience, more often than not, diffraction is just a topic that lets people have a discussion involving lots of big words. Sometimes it matters. Sometimes it's just a waste of time and energy. You have to figure out which. It's probably never worth getting your blood pressure elevated.

fantom Loc: Colorado

Joexx

Good summary

Urnst Loc: Brownsville, Texas

Thanks for your reply. I've decided not to worry about diffraction.