11-01-2010, 06:38 PM
[quote name='popo' timestamp='1288635643' post='3891']
I'm suffering from thinking fail at the moment introducing magnification into the equation. Is this a variation on the "equivalent FoV and equivalent effective aperture" at low magnifications?
In practical terms, at my level of macro photography I'm finding myself often balancing (badly) between adequate DoF and diffraction softening.
Let's take a simple case: say you have a 12MP APS-C sensor and 12MP FF sensor so we can disregard pixel count effects. For the equivalent *output* magnification, stopping down both systems to their respective diffraction limits, do you get the same or different DoF between them? Side question: does focal length factor in at all here or is it entirely due to magnification? (ignoring FoV effects)
[/quote]
You can ALWAYS disregard "pixel count effects" as they do not exist.
For every APS-C size sensor, diffraction is always the same. For every FF sensor, diffraction is always the same. Regardless of resolution/pixel count. Diffraction is ("sits") in the projected image. It does not matter at what rate you sample that projected image, the diffraction will not get worse or less.
Of course, the higher the sample "rate" (resolution), the more detailed the projected image gets registered.
With a higher res. sensor you can magnify (zoom in) the image more. So, you can see the diffraction effects more clearly, when you zoom in more. A lesser resolution would show the blocky pixels before you would be able to see the diffraction effects...
To answer your question:
Yes, diffraction "limits" show up at the same DOF. And that can be "calculated" simply by the crop factor. If you notice that you see diffraction softening of the image at a certain print size with FF at an f-stop of f11 for instance, you will notice the same diffraction softening of an image at a similar print size with APS-C at an f-stop of f11 / 1.6 (canon APS-C crop factor) = f6.9, so about f7.1.
I'm suffering from thinking fail at the moment introducing magnification into the equation. Is this a variation on the "equivalent FoV and equivalent effective aperture" at low magnifications?
In practical terms, at my level of macro photography I'm finding myself often balancing (badly) between adequate DoF and diffraction softening.
Let's take a simple case: say you have a 12MP APS-C sensor and 12MP FF sensor so we can disregard pixel count effects. For the equivalent *output* magnification, stopping down both systems to their respective diffraction limits, do you get the same or different DoF between them? Side question: does focal length factor in at all here or is it entirely due to magnification? (ignoring FoV effects)
[/quote]
You can ALWAYS disregard "pixel count effects" as they do not exist.
For every APS-C size sensor, diffraction is always the same. For every FF sensor, diffraction is always the same. Regardless of resolution/pixel count. Diffraction is ("sits") in the projected image. It does not matter at what rate you sample that projected image, the diffraction will not get worse or less.
Of course, the higher the sample "rate" (resolution), the more detailed the projected image gets registered.
With a higher res. sensor you can magnify (zoom in) the image more. So, you can see the diffraction effects more clearly, when you zoom in more. A lesser resolution would show the blocky pixels before you would be able to see the diffraction effects...
To answer your question:
Yes, diffraction "limits" show up at the same DOF. And that can be "calculated" simply by the crop factor. If you notice that you see diffraction softening of the image at a certain print size with FF at an f-stop of f11 for instance, you will notice the same diffraction softening of an image at a similar print size with APS-C at an f-stop of f11 / 1.6 (canon APS-C crop factor) = f6.9, so about f7.1.