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Old 03-01-2019   #23
retinax
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Quote:
Originally Posted by michaelwj View Post
One thing that always bugs me about "equivalency" is depth of field. /rant on/

Larger format users correctly point to the thinner depth of field at a specific aperture. You need a brighter (and therefore bigger and more expensive) lens in a smaller format to achieve the same shallow depth of field. A full frame f/1.4 lens would need an f/1.0 APSC, and an f/0.7 m43 lens. That's fine, the advantage is in the larger format (up to full frame anyway).

But, the counter argument doesn't fly unless you are hitting your minimum aperture. You don't get more depth of field with a smaller format because you can just stop down another stop with no cost/size/weight penalty. For cameras with the same pixel count, diffraction will set in at m43 one stop earlier than APSC, and two stops earlier than full frame. For example, a m43 landscape shot at f/8 will show the same level of diffraction as an APSC shot at f/11 and full frame shot at f/16. The only limiting factor is if we shoot m43 at f/11 and our full frame lens doesn't go to f/22. Diffraction from an f/16 aperture is greater than at f/8, with the diffraction is being spread over twice the angular range. But the bigger sensor has twice the angular range to compensate (for the same number of pixels the pixels will be twice the width, the diffraction will be the same at a per pixel level). It makes no difference. Increasing the resolution in the larger sensor means you'll see diffraction at a pixel level earlier, but the final print will look be sharper.

/rant over/ for now...
No-one disputes that one can stop down. However Ming Thein talks about hand held photography, so the price to pay for stopping down beyond a certain point is higher ISO, as he points out. Which may still be better, or not.
For tripod photography your point stands. Even more, I doubt that diffraction actually doubles per f/stop down that is needed to get the same dof for FF compared to APS-C, because the length of the edge of the diaphragm (which is responsible for diffraction) doesn't change in a linear way with the size of the aperture. Or does it? Maybe because we need to consider the different aperture size needed for the different focal length to get the same fov. Ok I'm in over my head.
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