Diffraction Limit Discussion Continuation

Started Feb 21, 2014 | Discussions thread
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bobn2 wrote:

Jonny Boyd wrote:

bobn2 wrote:

I think that the semantic argument that this discussion tends to end up in (maybe when the 'peak aperture shifts' people realise that they are wrong) is missing the point of the misinformation and damage to practice that this meme causes. Whatever they wish to decide that they really meant in this abstruse semantic discussion, there are many photographers who look at sites such as CiC, and posts here inspired by it, and end up believing that a low pixel count camera will give them sharper results at small apertures than will a high pixel count camera (absurdities like 'D800 unusable above f/5.6'). While I'm quite prepared to believe that wasn't what they really meant, I'd be more impressed had they made that point in the original posts where they claimed there was a 'diffraction limit'.

I don't recall anyone saying that a low pixel count camera will be sharper than a high res camera (if by sharpness you mean overall image detail).

maybe that hasn't been said explicitly (can't be bothered to go through the whole thread to search) but undoubtedly that is how this bogus 'diffraction limit' gets understood.

Exactly.  For example, to the uneducated on diffraction, if you say one system is "diffraction limited at f/4" and another system is "diffraction limited at f/5.6", they take it to mean that the system that is "diffraction limited at f/4" will deliver a lower resolution photo at f/5.6 than the system that is "diffraction limited at f/5.6".

In fact I recall plenty of instances where people have affirmed that although diffraction is visible earlier in high pixel count cameras, they still have more overall detail than a low pixel count camera. What you're saying sounds more like misinformation by suggesting that anyone is making that claim.

I'm basing on what I see understood by it. If we all agree that you still get more detail, what is the point of worrying about this 'diffraction limit' at all?

Exactly.  First of all, for a given lens, if the peak aperture is f/4 on one sensor, then it will be f/4 on all other sensors.  More importantly, however, is that it doesn't matter what the peak aperture is unless the whole of what you want in the DOF is within the DOF.

Specifically, if you need f/8 to get everything you want within the DOF, then f/8 resolves better than f/4, even if f/4 is the peak aperture of the system.  On the other hand, if f/4 resolves significantly better than f/8, then the photographer may choose instead to use focus stacking, scene permitting.

So, to recap, if the peak aperture of a lens on one sensor is f/4, then it will be f/4 for all other sensors, but the higher MP sensor will resolve more detail, all else equal.  However, if DOF constraints require a smaller aperture, then the smaller aperture will give better results than the peak aperture for a single exposure.

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