11-03-2010, 09:26 AM
Hi Serkan,
I'll keep it short... <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.
[quote name='PuxaVida' timestamp='1288769977' post='3932']
Well, I must say I'm a bit confused, that's absolutely correct... To be more precise let me explain the cases which I have in mind:
1) Two 1,5x cropped sensors with different pixel densities (e.g. 12mp vs. 18mp). Two images are shot at F13 (same lens) and they are printed on a 60x90 paper. Compare the effects of diffraction on both prints.[/quote]
Diffraction effects exactly the same.
Less diffraction with the FF prints.
Diffraction advantage (less diffraction) to FF.
You can't multiply apertures by a factor. You first have to work out what the factor means in f-stops.
However, using an f-stop on FF equivalent to the f-stop on APS-C to get the same DoF and the same framing, they will both show the same amount of diffraction.
Do note, BTW, that diffraction is always present, basically because you are shooting through an aperture. However, this is an exponentially gliding scale, as in, diffraction gets exponentially worse with closing down the aperture, and sensor size, or rather, CoC, plays an important factor. CoC is determined on the magnification factor required to see an image with sharp details, an image of A4 size for ease of reference, at a distance of 30 cm, with a resolution of 6-8 lp/mm, which is apparently the acuity of the human eye at that distance. In order to get that sharpness, you need a CoC of 0.3 mm for FF, and about 0.2 mm for APS-C, which is why with the latter the diffraction hits sooner.
What does it mean that diffraction "hits"? In simple terms, that the effects of diffraction overshadow the gain in DoF you would get from stopping down further. IOW, roughly from F/13 on APS-C and from F/18 on FF you don't get added benefit from stopping down further, because the fuzziness caused by diffraction will hide the additional gain in DoF. However, it also depends on the size of the print. Pritn smaller, and the effective sharpness increases, etc.
Finally, thsi si really only a guide. Having shot a lot of macro over the past 38 years or so, I always found that in a lot of cases extra DoF does trump diffraction. This is caused really by the fact that at macro level we have really nothing to compare with, and that even very low resolutions with smooth transitions look better than nothing at all. And thsi also varies from lens to lens. A lens with extremely good microcontrast, f.e., creating the illusion of sharpness essentially, may actually provide better pictures at F/22 than another lens which doesn't. There are really many factors at play in this.
It is possible to determine absolute values for diffraction by aperture, as they essentially are dependent only on aperture. However, you need to take the magnification into account when looking at prints, and this is where the difficulty, subjectivity sensor size, magnification used, etc., come into play. The more you enlarge, the more you will see the effects of diffraction (note that for a FF sensor you have to magnify 1.5 or 1.6X less, linear, than with APS-C). Thus, the maximum resolution of a lens at a certain diffraction limited lens, when used on FF vs APS-C, will show up diffraction effects sooner on APS-C than on FF, in principle by a straight factor of 1.5 or 1.6X, although that has to be converted to f-stops to make comparisons possible at all (i.e, convert to area first, convert that to f-stops, and add that, or rather subtract that when going from FF to APS-C).
Oops... I said I would keep it short... Better stop now <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.
Kind regards, Wim
I'll keep it short... <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.[quote name='PuxaVida' timestamp='1288769977' post='3932']
Well, I must say I'm a bit confused, that's absolutely correct... To be more precise let me explain the cases which I have in mind:
1) Two 1,5x cropped sensors with different pixel densities (e.g. 12mp vs. 18mp). Two images are shot at F13 (same lens) and they are printed on a 60x90 paper. Compare the effects of diffraction on both prints.[/quote]
Diffraction effects exactly the same.
Quote:2) One 1,5x cropped sensor, one FF sensor with the same pixel sizes. Two images are shot at F13 (different DoF, same lens, different subject distance to provide the same FoV). Print on 60x90 and check the effects of diffraction.
Less diffraction with the FF prints.
Quote:3) One 1,5x cropped sensor, one FF sensor (same sensor resolution, FF has bigger pixels). Two images are shot at F13. Same DoF, same lens, different subject distance to provide the same FoV. Print on 60x90 and check the effects of diffraction.
Diffraction advantage (less diffraction) to FF.
Quote:4) One 1,5x cropped sensor, one FF sensor (same sensor resolution, FF has bigger pixels). Two images are shot at F12 (1,5x) and F18 (FF). Same DoF, same lens, different subject distance to provide the same FoV. Print on 60x90 and check the effects of diffraction.
You can't multiply apertures by a factor. You first have to work out what the factor means in f-stops.
However, using an f-stop on FF equivalent to the f-stop on APS-C to get the same DoF and the same framing, they will both show the same amount of diffraction.
Quote:Kind regards,
Serkan
Do note, BTW, that diffraction is always present, basically because you are shooting through an aperture. However, this is an exponentially gliding scale, as in, diffraction gets exponentially worse with closing down the aperture, and sensor size, or rather, CoC, plays an important factor. CoC is determined on the magnification factor required to see an image with sharp details, an image of A4 size for ease of reference, at a distance of 30 cm, with a resolution of 6-8 lp/mm, which is apparently the acuity of the human eye at that distance. In order to get that sharpness, you need a CoC of 0.3 mm for FF, and about 0.2 mm for APS-C, which is why with the latter the diffraction hits sooner.
What does it mean that diffraction "hits"? In simple terms, that the effects of diffraction overshadow the gain in DoF you would get from stopping down further. IOW, roughly from F/13 on APS-C and from F/18 on FF you don't get added benefit from stopping down further, because the fuzziness caused by diffraction will hide the additional gain in DoF. However, it also depends on the size of the print. Pritn smaller, and the effective sharpness increases, etc.
Finally, thsi si really only a guide. Having shot a lot of macro over the past 38 years or so, I always found that in a lot of cases extra DoF does trump diffraction. This is caused really by the fact that at macro level we have really nothing to compare with, and that even very low resolutions with smooth transitions look better than nothing at all. And thsi also varies from lens to lens. A lens with extremely good microcontrast, f.e., creating the illusion of sharpness essentially, may actually provide better pictures at F/22 than another lens which doesn't. There are really many factors at play in this.
It is possible to determine absolute values for diffraction by aperture, as they essentially are dependent only on aperture. However, you need to take the magnification into account when looking at prints, and this is where the difficulty, subjectivity sensor size, magnification used, etc., come into play. The more you enlarge, the more you will see the effects of diffraction (note that for a FF sensor you have to magnify 1.5 or 1.6X less, linear, than with APS-C). Thus, the maximum resolution of a lens at a certain diffraction limited lens, when used on FF vs APS-C, will show up diffraction effects sooner on APS-C than on FF, in principle by a straight factor of 1.5 or 1.6X, although that has to be converted to f-stops to make comparisons possible at all (i.e, convert to area first, convert that to f-stops, and add that, or rather subtract that when going from FF to APS-C).
Oops... I said I would keep it short... Better stop now <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.Kind regards, Wim
Gear: Canon EOS R with 3 primes and 2 zooms, 4 EF-R adapters, Canon EOS 5 (analog), 9 Canon EF primes, a lone Canon EF zoom, 2 extenders, 2 converters, tubes; Olympus OM-D 1 Mk II & Pen F with 12 primes, 6 zooms, and 3 Metabones EF-MFT adapters ....