End of Megapixel wars and EF-S buying decisions

Started Feb 23, 2006 | Discussions thread
OP David Martin Forum Pro • Posts: 17,056
Re: Diffraction theory too difficult for me..

The only thing I can say is that I don't know.

I started a thread a while back, asking if diffraction was a problem for the 20D, and some of the real heavyweights here got interested - I couldn't really follow most of the arguments, and the dispute amoungst the big boys got quite heated with them chucking nquist curves around the place.

In fact, it got so technical that I did not even bookmark the thread, just the theory page on diffraction I linked.

In so far as I understood it though, most seemed to think that diffraction in practise anyway was linked to pixel size, and that with smaller pixels diffraction limits kicked in at larger and larger F stops - in practise the D2X was a bit of a limiting case, and much more density than that and it started to be something that you would have to be thinking about when you were shooting - but I may have totally misunderstood.

U Sererra wrote:

Hi David,
I read your diffraction-related link a few days ago, and what I
took from it is this:
At least in theory, the diffraction limit is the same for the same
depth-of-field, regardless of sensor size.
The upshot of this is a larger sensor size will hit the diffraction
limit at a smaller aperture, BUT that's the aperture you'd need to
use to get the same depth-of-field as you would when using whatever
aperture causes the diffraction limit to kick in on a smaller

I understand that reality is a bit different from theory (competing
factors can place the optimum sharpness f-stop past the diffraction
limit), but theoretically diffraction limit is not a specific or
worsening problem for smaller sensor sizes.

A 16MP APS-C sensor will hit diffraction limit at Aperture X.
A 16MP FF sensor will hit diffraction limit at Aperture Y.

APS-C sensor will get DOF Z at Aperture X.
FF sensor will also get DOF Z at Aperture Y.

So, the lower f-stop value for the smaller sensor is not
neccessarily a problem.

When I discovered this I became more comfortable with sticking to
the 1.6 form factor.

Have I correctly understood the theory expounded on that webpage?

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