FF cropping vs APS-C

Started 4 months ago | Questions thread
preferredfault Regular Member • Posts: 328
Re: FF cropping vs APS-C

Perhaps this isn't exactly what you're looking for, but I think what I'm about to say is somewhat relevant.

Firstly, since we can't really increase the density of glass, using a smaller piece of glass to produce the same image, generally results in lower quality. This isn't the rule, because it depends on a lot of factors, but it's a reason why a lot of cheap zooms are bad quality.....they're using just a tiny fraction of the glass in the center to create an image.

Secondly, sensor size and resolution of that sensor, actually determine the diffraction limit, meaning you're going to get diffraction at a given aperture depending on your sensor size and its resolution. For example, on APSC sized sensors of 20MP, the math for diffraction calculations say that at around f/7.7 is when diffraction will start creeping in. Move up to full frame with 20MP, and diffraction starts creeping in at f/12. Move down to 1/2.3 sensor size with 20MP, and diffraction will start creeping in at f/2.3!

Of course, that doesn't mean diffraction will immediately begin to ruin your image quality in a very noticeable way, but something people don't talk about is that the smaller the sensor, the more diffraction limited you are, given the same resolution. This is why for example, tiny sensor super zooms are pretty soft (because they usually have apertures of f/4-f/8, which is actually equivalent to ~f/22-f/40!) but f/1.8 lenses on phones can be pretty sharp with much less glass.

But the point is, this can all affect cropping on FF/APSC. For example, a person might be doing landscape with APSC and think "I gotta stop down that aperture to f/12!". But in reality, they will have likely created a softer image than if they shot at f/8 or less. And cropping a softer image is obviously going to affect detail/clarity. This information might not be immediately useful for general usage, but it can come in handy at some point.

To give you actual numbers of the diffraction limit for your camera's:

60D: f/8

6D2: f/11

Never go above these, regardless of the lens, and you'll generally have the sharpest images possible, that can be better cropped.

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