02-08-2012, 04:59 AM
[quote name='wim' timestamp='1328606822' post='15620']
The Nyquist resolution is approximately 103 lp/mm, so I don't see any problems here. Same resoltuion as low iso (iso 25-50) "normal use" B&W film.
Of course, I have mentioned this before, the whole diffraction thing is totally out of context. When looking at the Nyquist frequency, and at good old film resolution, there is a severe mismatch in all of these discussions: we used to shoot quite happily with film, without worrying about emulsion diffraction. And it suffers from exactly the same problem - silver halide grain size in an emulsion is very uniform in size, it just isn't lined up as nicely as sensels are.
Anyway, based on my calculation, using the Rayleigh criterion, sensor diffraction limit for the sensor is F/16, which only means that from that aperture onwards, towards smaller apertures, lens resolution due to lens diffraction is less than the sensor resolution. As we still have the lens formula at F/16 we will still end up with a system resolution of 51 lp/mm, which is professional type resolution from a 35 mm size image on film, and 1.25 X to 2.5 X higher than an enthousiast would be able to capture. Note that on film we would capture these resolutions at much larger apertures, liek F/4 and F/5.6 (all due to system resolution and development and printing process): it is therefore quite a step forward
In short, no need to worry. If anything, it is to be applauded.
Kind regards, Wim
[/quote]
Thank you for your clarification and explanation, Wim. I took a look at the pz test result of the Nikon 14-24mm lens on DX3, the central resolution power (MTF50) of the lens before diffraction coming in is very close to the resolution power of D3x, which is 84 lp/mm. Seems not a problem for D800, whose resolution power is 103 lp/mm as pointed out by you. The border resolution may be a different story, but seems not bad for the 14-24mm lens. (I know that this kind of comparison between cameras may not be inaccurate, but perhaps not totally wrong.)
While for diffraction, you stated that "sensor diffraction limit for the sensor is F/16", while my estimation is around f/7 for green light of wavelength 555nm. I would like to tell you how I did the calculation and check with you if I have made some mistake.
The angular diameter of the Airy disk of light diffraction is a=1.22L/D, where L is the wavelength of the light, D is the diameter of the lens' aperture. Since D=f/N, f is the focal length and N is the aperture, the linear diameter of the Airy disk on the image sensor is then (when focused at infinity) p=af=1.22LN. The pixel square of D800 has a side of length p0=0.0049mm=4900nm. Then, the aperture when p=p0 is N=p0/1.22L. For red light of 750nm, I get N=5.4. For blue light of 390nm, I get N=10. For green light of 555nm (which human eye is most sensitive to), I get N=7.2. Could you tell me how did you get the f/16? Had we used different criteria?
Any way, my worrisome is that when the resolution of the sensor is much larger than the resolution of the lens, if the extra resolution of the sensor still useful. I have no experience with films. But I know that the 35mm black and white film usually has a resolution much larger than the lens. But I also heard that finer films can diplay more details in the image, although I don't understand why.
Best regards,
Frank
The Nyquist resolution is approximately 103 lp/mm, so I don't see any problems here. Same resoltuion as low iso (iso 25-50) "normal use" B&W film.
Of course, I have mentioned this before, the whole diffraction thing is totally out of context. When looking at the Nyquist frequency, and at good old film resolution, there is a severe mismatch in all of these discussions: we used to shoot quite happily with film, without worrying about emulsion diffraction. And it suffers from exactly the same problem - silver halide grain size in an emulsion is very uniform in size, it just isn't lined up as nicely as sensels are.
Anyway, based on my calculation, using the Rayleigh criterion, sensor diffraction limit for the sensor is F/16, which only means that from that aperture onwards, towards smaller apertures, lens resolution due to lens diffraction is less than the sensor resolution. As we still have the lens formula at F/16 we will still end up with a system resolution of 51 lp/mm, which is professional type resolution from a 35 mm size image on film, and 1.25 X to 2.5 X higher than an enthousiast would be able to capture. Note that on film we would capture these resolutions at much larger apertures, liek F/4 and F/5.6 (all due to system resolution and development and printing process): it is therefore quite a step forward
In short, no need to worry. If anything, it is to be applauded.
Kind regards, Wim
[/quote]
Thank you for your clarification and explanation, Wim. I took a look at the pz test result of the Nikon 14-24mm lens on DX3, the central resolution power (MTF50) of the lens before diffraction coming in is very close to the resolution power of D3x, which is 84 lp/mm. Seems not a problem for D800, whose resolution power is 103 lp/mm as pointed out by you. The border resolution may be a different story, but seems not bad for the 14-24mm lens. (I know that this kind of comparison between cameras may not be inaccurate, but perhaps not totally wrong.)
While for diffraction, you stated that "sensor diffraction limit for the sensor is F/16", while my estimation is around f/7 for green light of wavelength 555nm. I would like to tell you how I did the calculation and check with you if I have made some mistake.
The angular diameter of the Airy disk of light diffraction is a=1.22L/D, where L is the wavelength of the light, D is the diameter of the lens' aperture. Since D=f/N, f is the focal length and N is the aperture, the linear diameter of the Airy disk on the image sensor is then (when focused at infinity) p=af=1.22LN. The pixel square of D800 has a side of length p0=0.0049mm=4900nm. Then, the aperture when p=p0 is N=p0/1.22L. For red light of 750nm, I get N=5.4. For blue light of 390nm, I get N=10. For green light of 555nm (which human eye is most sensitive to), I get N=7.2. Could you tell me how did you get the f/16? Had we used different criteria?
Any way, my worrisome is that when the resolution of the sensor is much larger than the resolution of the lens, if the extra resolution of the sensor still useful. I have no experience with films. But I know that the 35mm black and white film usually has a resolution much larger than the lens. But I also heard that finer films can diplay more details in the image, although I don't understand why.
Best regards,
Frank