11-21-2011, 01:58 PM
[quote name='wim' timestamp='1321881331' post='13112']
That actually depends on the size of the CoC vs the size of the resolved detail. Anything with grains larger than what the CoC prescribes, actually appears unsharp. Those individual "grains" may well look sharp, but DoF disappears. DoF and CoC go hand in hand. As does viewing distance and/or print size. This is what I am trying to indicate all the time. DoF is related to a certain viewing distance, a certain print size and a certain resolution.
That DoF is perceived by you to be independent of those, is probably because you are essentially looking at just the definition of DoF as a given, which is based on a certain CoC for a certain recording medium size. You somehow don't seem to take into account that all of those variables influence DoF.
Only up to a certain point.
I happen to have two images on my wall(s), 60 cm by 90 cm both. One taken at 21 MP, the other at 8 MP. If I am standing at the same (too short) viewing distance, the 8MP does show very sharp grains, the other doesn't show grains yet. DoF in the 8MP image is no longer there at that point, even though it is in the 21 MP one.
Stepping back far enough I can't really see the individual grains anymore, the situation changes - DoF is there.
As I tried to explain, there is an interrelationship between image magnification and image size, viewing distance, and resolution, which all determine DoF (in conjunction with aperture of course - and therefore also diffraction and size of Airy disks...). And there is a standard definition for this, namely a print of 30 cm diagonally, 30 cm viewing distance, resolution on print of (at least) 6 lp/mm. for the sharp areas. This is achieved on FF, resolution of sensor permitting, with a CoC of 0.30 mm. Anything with less resolution, at this definition, humans, on average, do not perceive as in focus and sharp, and hence also outside the DoF zone.
[url="http://www.cambridgeincolour.com/tutorials/depth-of-field.htm"]http://www.cambridge...th-of-field.htm[/url]
[url="http://photo.net/learn/optics/lensTutorial#part3"]http://photo.net/lea...sTutorial#part3[/url]
[url="http://toothwalker.org/optics/dof.html"]http://toothwalker.org/optics/dof.html[/url]
[url="http://www.normankoren.com/Tutorials/MTF6.html"]http://www.normankor...rials/MTF6.html[/url]
[url="http://www.normankoren.com/Tutorials/MTF.html#Human_visual_acuity"]http://www.normankor...n_visual_acuity[/url]
[url="http://www.stanford.edu/class/ee368b/Handouts/09-HumanPerception.pdf"]http://www.stanford....nPerception.pdf[/url]
I can't find the exact link anymore on human visual acuity and the effect on perceived sharpness, but when I do find that, I will add that here too.
The point I was trying to make, is that in case resolution is not high enough, it will only look sharp from a larger viewing distance. DoF takes a certain CoC into account, which incoporates human visual acuity. If the resolution is not up to scratch, the picture is not sharp and doesn't appear to be in focus, hence not in DoF, at best the pixels or grains are sharp, but those are regardless.
DoF is defined based on a standard, which involves CoC, and therefore viewing distance, print size and resolution, and obviously aperture. Aperture and AoV do matter indeed, because those determine DoF based on a certain CoC. And there is the catch.
Kind regards, Wim
[/quote]
Really useful links and explanations. Again, thanks Wim.
That actually depends on the size of the CoC vs the size of the resolved detail. Anything with grains larger than what the CoC prescribes, actually appears unsharp. Those individual "grains" may well look sharp, but DoF disappears. DoF and CoC go hand in hand. As does viewing distance and/or print size. This is what I am trying to indicate all the time. DoF is related to a certain viewing distance, a certain print size and a certain resolution.
That DoF is perceived by you to be independent of those, is probably because you are essentially looking at just the definition of DoF as a given, which is based on a certain CoC for a certain recording medium size. You somehow don't seem to take into account that all of those variables influence DoF.
Only up to a certain point.
I happen to have two images on my wall(s), 60 cm by 90 cm both. One taken at 21 MP, the other at 8 MP. If I am standing at the same (too short) viewing distance, the 8MP does show very sharp grains, the other doesn't show grains yet. DoF in the 8MP image is no longer there at that point, even though it is in the 21 MP one.
Stepping back far enough I can't really see the individual grains anymore, the situation changes - DoF is there.
As I tried to explain, there is an interrelationship between image magnification and image size, viewing distance, and resolution, which all determine DoF (in conjunction with aperture of course - and therefore also diffraction and size of Airy disks...). And there is a standard definition for this, namely a print of 30 cm diagonally, 30 cm viewing distance, resolution on print of (at least) 6 lp/mm. for the sharp areas. This is achieved on FF, resolution of sensor permitting, with a CoC of 0.30 mm. Anything with less resolution, at this definition, humans, on average, do not perceive as in focus and sharp, and hence also outside the DoF zone.
[url="http://www.cambridgeincolour.com/tutorials/depth-of-field.htm"]http://www.cambridge...th-of-field.htm[/url]
[url="http://photo.net/learn/optics/lensTutorial#part3"]http://photo.net/lea...sTutorial#part3[/url]
[url="http://toothwalker.org/optics/dof.html"]http://toothwalker.org/optics/dof.html[/url]
[url="http://www.normankoren.com/Tutorials/MTF6.html"]http://www.normankor...rials/MTF6.html[/url]
[url="http://www.normankoren.com/Tutorials/MTF.html#Human_visual_acuity"]http://www.normankor...n_visual_acuity[/url]
[url="http://www.stanford.edu/class/ee368b/Handouts/09-HumanPerception.pdf"]http://www.stanford....nPerception.pdf[/url]
I can't find the exact link anymore on human visual acuity and the effect on perceived sharpness, but when I do find that, I will add that here too.
The point I was trying to make, is that in case resolution is not high enough, it will only look sharp from a larger viewing distance. DoF takes a certain CoC into account, which incoporates human visual acuity. If the resolution is not up to scratch, the picture is not sharp and doesn't appear to be in focus, hence not in DoF, at best the pixels or grains are sharp, but those are regardless.
DoF is defined based on a standard, which involves CoC, and therefore viewing distance, print size and resolution, and obviously aperture. Aperture and AoV do matter indeed, because those determine DoF based on a certain CoC. And there is the catch.
Kind regards, Wim
[/quote]
Really useful links and explanations. Again, thanks Wim.