09-25-2011, 09:44 AM
[quote name='wim' timestamp='1316909344' post='11825']
This whole issue about a sensor outresolving a lens is a bit of a non-issue, as it is purely determined by diffraction. We never worried about this with film, and it plays a just as important role with film as it does with a sensor, even though we never talked about thsi in the film era.
At a certain point, when stopping down the aperture, the resolution of the sensor will be bigger than that of a lens, when the Nyquist frequency for a sensor outnumbers the resolution possible at a certain diffraction limit, so well, fine. For the Nikon V1 / J1, with a pixel size of 3.2 micron, this point will be reached at F/11, for a 1.6X crop factor camera like the 7D (4.24 micron sensel size) this is at F/14, for a FF camera like the 5D II (6.32 micron) this is at F/20. The question is whether this is important at all, because it just means that the sensor can provide detail over an area where the lens can no longer. At that point, the resolution of the sensor is for V1/J1 147 lp/mm, for 7D 118 lp/mm, and for 5D II 78 lp/mm. Since the best lenses will do 400 lp/mm at F/4 (diffraction limited, based on air images, i.e., instumentally measured), and that is pretty much independent of FL when it comes to (very good) photographic lenses which are somewhere around a "normal" FL (say 24-150 mm FF equivalent, although there are exceptions both in lower and higher FLs), this is a bit of a moot point, even though many people worry about it.
It does essentially still mean that despite the high resolution of the sensors of smaller cameras, the images still can't be enlarged as much as for those from cameras with larger sensors, exactly because the sensors are smaller. 8.8 X 147 (V1/J1, 1293 lp) is less than 14.9 X 118 (7D, 1758 lp), and that is less again then 24 X 78 (1872 lp). And this is without taking DR and SNR into account.
BTW, for an A4 image at normal viewing distance one really needs 1443 lp based on the capabilities of the human eye. All of this based on the short side of sensors and image. For a 10 cm X 15 cm print, the short side requires 688 lp. Before I forget, lp stands for line pairs. In order to distinguish anything at all, humans need a contrast transition imaged by means of two lines (or more), hence the use of line pairs.
Kind regards, Wim
[/quote]
The best SLR lenses rarely achieve over 100lp/mm.
The diffraction limits you talk about seem to be based in a very specific wavelength of monochromatic light. With a normal light spectrum, diffraction limited resolution sets it way sooner. Your 400 lp/mm at f4 sits very close to g-line wavelength, which is in the ultra violet part of the spectrum (wavelength 435.8mm, 470 lp/mm). So I think the poster above putting it in the blue part of the spectrum is possibly right.
You will see diffraction limiting resolution from about f4 and up, with the Nikon 1 system. That is on pixel level of course, and I agree with you that, like in the film era, we should not put too much importance in diffraction softening of the projected image.
This whole issue about a sensor outresolving a lens is a bit of a non-issue, as it is purely determined by diffraction. We never worried about this with film, and it plays a just as important role with film as it does with a sensor, even though we never talked about thsi in the film era.
At a certain point, when stopping down the aperture, the resolution of the sensor will be bigger than that of a lens, when the Nyquist frequency for a sensor outnumbers the resolution possible at a certain diffraction limit, so well, fine. For the Nikon V1 / J1, with a pixel size of 3.2 micron, this point will be reached at F/11, for a 1.6X crop factor camera like the 7D (4.24 micron sensel size) this is at F/14, for a FF camera like the 5D II (6.32 micron) this is at F/20. The question is whether this is important at all, because it just means that the sensor can provide detail over an area where the lens can no longer. At that point, the resolution of the sensor is for V1/J1 147 lp/mm, for 7D 118 lp/mm, and for 5D II 78 lp/mm. Since the best lenses will do 400 lp/mm at F/4 (diffraction limited, based on air images, i.e., instumentally measured), and that is pretty much independent of FL when it comes to (very good) photographic lenses which are somewhere around a "normal" FL (say 24-150 mm FF equivalent, although there are exceptions both in lower and higher FLs), this is a bit of a moot point, even though many people worry about it.
It does essentially still mean that despite the high resolution of the sensors of smaller cameras, the images still can't be enlarged as much as for those from cameras with larger sensors, exactly because the sensors are smaller. 8.8 X 147 (V1/J1, 1293 lp) is less than 14.9 X 118 (7D, 1758 lp), and that is less again then 24 X 78 (1872 lp). And this is without taking DR and SNR into account.
BTW, for an A4 image at normal viewing distance one really needs 1443 lp based on the capabilities of the human eye. All of this based on the short side of sensors and image. For a 10 cm X 15 cm print, the short side requires 688 lp. Before I forget, lp stands for line pairs. In order to distinguish anything at all, humans need a contrast transition imaged by means of two lines (or more), hence the use of line pairs.
Kind regards, Wim
[/quote]
The best SLR lenses rarely achieve over 100lp/mm.
The diffraction limits you talk about seem to be based in a very specific wavelength of monochromatic light. With a normal light spectrum, diffraction limited resolution sets it way sooner. Your 400 lp/mm at f4 sits very close to g-line wavelength, which is in the ultra violet part of the spectrum (wavelength 435.8mm, 470 lp/mm). So I think the poster above putting it in the blue part of the spectrum is possibly right.
You will see diffraction limiting resolution from about f4 and up, with the Nikon 1 system. That is on pixel level of course, and I agree with you that, like in the film era, we should not put too much importance in diffraction softening of the projected image.