Canon Announces EOS 60D Digital SLR Camera

[canoli]

yikes - that means I've been thinking about DLA completely wrong - the truth is a lower f/stop is the better body spec, right?


So camera sensors limit rez below a certain aperture, and lenses limit rez above a certain aperture...that means the only diffraction-free apertures are between those 2 limits. Is that the right way to think about it? And as the f/stop spec on a body comes down, the wider that range gets?


As an aside, we are talking 100% pixel views here, right? So maybe the effect has little, if any, real-world significance? (I don't mean to suggest it's irrelevant and I'd still like to understand it)


Sorry, I'm like a 50D sensor I guess - dense! I have a bad feeling I've still got it all balled up. Any help will be greatly appreciated...thanks!

[Jon Ruyle]

The effect of diffraction on a picture is simple. Each point of light passing through the lens turns into a disc. The overall effect of this is to blur the picture. The bigger the disc, the more blurry the picture is. This happens with all lenses, but a bigger aperture makes a smaller disc (sharper picture). DLA is the f number at which the size of the disc equals the size of a pixel.

So camera sensors limit rez below a certain aperture, and lenses limit rez above a certain aperture...that means the only diffraction-free apertures are between those 2 limits. Is that the right way to think about it?

I would think about it like this: 1) f number limits resolution. The smaller the f number, the higher the resolution you can have. 2) Sensor limits resolution. The more megapixles, the higher the resolution. 3) Your pictures resolution will be limited by the worse of these two limits 4) DLA is where these limits are the same. A higher resolution camera will be the equal of a larger aperture lens, and thus have a lower DLA.


There are no "diffraction free" apertures. Diffraction is always there, but in some cases it is small enough to be hidden by sensor resolution (blur discs are smaller than a pixel). Of course, higher resolution sensors reveal diffraction more often. Some people misunderstand and think higher resolution sensors "have more diffraction", but that is not true. (We all know that a higher resolution sensor can reveal more optical flaws in a lens, but that doesn't mean those flaws aren't there when using a low resolution sensor. Same idea here.)

So maybe the effect has little, if any, real-world significance?

Often, diffraction is not an issue. But sometimes (notably for macros and landscapes) it can be the limiting factor in resolution.

[canoli]

Thanks Jon - can't say I quite get the concept yet but I'm getting there, and I thank you for elaborating on the subject.