Quote:No, but but system resolution can in simple form be calculated with the old formula for this:

 

1/(system resolution) = 1/(lens resultion at specific f-stop) + 1/(sensor resolution)

 

For ease of use we are assuming that we are talking base iso for a sensor, and in that case sensor resolution is in principle equal to the nyquist frequency, plus or minus 5 to 15 % depending on de AA-filter stack being used.although fro ease of use we can ignore this.

 

Generally speaking, in the olden days, we worked all of this back to lp/mm, and for a 16 MP MFT sensor you then end up at approximately 133 lp/mm, for a 20 MP MFT sensor at base iso that is 150 lp/mm. If we assume a 10% reduction due to the AA-fiter, this then becomes approximtely 120 lp/mm and 135 lp/mm.

 

For diffraction based maximum lens resolution, we used to use the so-called Rayleigh criterion, and that amounts to using a wavelength of 512 Angstrom and an MTF of approximately 9%, which for normal shooting purposes is average. Note that MTF-50s are therefore typically a lot lower. Anyway, at F/1 the Rayleigh limit is about 1600 lp/mm, based on the Airy disk size, the diffraction circle size of a point, one gets at these parameters.

 

Because of diffraction, we then roughly get the following diffraction limits for perfect lenses at different f-stops, all based on the Rayleigh criterion:

 

F/1: 1600 lp/mm

F/1.4: 1143 lp/mm

F/2: 800 lp/mm

F/2.8: 571 lp/mm

F/4: 400 lp/mm

F/5.6: 286 lp/mm

F/8: 200 lp/mm

F/11: 145 lp/mm

F/16: 100 lp/mm

etc.

 

Now, there is no such thing as a perfect lens, and off-axis performance of a lens deteriorates as well, and at large apertures a lens is generally not at its best. However, many of the high quality lenses do rather well when stopped down a few stops, and some even get close if not equal diffraction limits at those f-stops, at least in the optical centre.

 

Because lenses tend to be best when stopped down a bit, generally speaking, and because diffraction gets worse with stopping down, what often happens when you measure lens resolution, is that the resolution starts at a specific point, gets higher, and when diffraction becomes teh limiting factor, lens resolution goes down again. You get a parabolic or elliptical type curve, with the top lying often at the f-stops a few stops away from maximum aperture.

 

The so-called diffraction limit of sensors, essentially is the aperture at which point a sensor cannot resolve beyond teh diffraction limit, purely caused by the fact that lights bend. It is a bit more complex than that, because sensor wells are indeed wells, and create shadows depending on the angle of the incoming light, but roughly this is correct. For MFT sensors at 16 MP and 20 MP these sensor diffraction limits are F/12 and F/11 respectively, but to get the most out of this you generally need to stop down  a full aperture less, so F/9 and F/8. it doesn't mean you can't take a picture, or can't get a usable image, but this is about making optimal use of what is available; the resolution of the sensor does not alter regardless.

 

As many testers use MFT-50 for their resolution findings, I have also calculated a set of MTF-50 diffraction limits. Here it is;

 

F/1: 760 lp/mm

F/1.4: 543 lp/mm

F/2: 380 lp/mm

F/2.8: 271 lp/mm

F/4: 190 lp/mm

F/5.6: 136 lp/mm

F/8: 95 lp/mm

F/11: 69 lp/mm

F/16: 48 lp/mm

etc.

 

I have created a few tables in which I also calculated the system resolution for different sensors, and perfect lenses, based on teh two diffraction limits I mentioned here (rayleigh criterion and MTF-50).

 

First, Panasonic Lumix GF2, a 12 MP MFT camera:
Panasonic GF2.jpg

 

Olympus O-MD E-M10 Mark II (16 MP, same as O-MD E-M5, etc.):
OMD-EM10-II.jpg

 

Olympus Pen F, 20 MP (same as Panasonix GX8):
pen-f.jpg

 

In short, as you can see, at F/4, 12 MP and MTF-50 maximum resolution is 72 lp/mm, at F/4, 16 MP and MTF-50 it is 78 lp/mm and at F/4, 20 MP and MTF-50 it is 84 lp/mm. Similarly, at F/5.6 it is 62 lp/mm, 67 lp/mm, and 71 lp/mm respectively. At apertures larger than F/4 lenses tend to have a lot of residual errors and resolve less, and as you can see at F/5.6 diffraction already starts to become signifcant (for any lens and any system).

 

Even so, resolution is well above what we used to have with film, as I mentioned before, in other posts.

 

HTH, kind regards, Wim

Quote:interesting that the different wavelengths of light effectively cause different resolution limits. Going back to the 100-400, from the tables Klaus linked to at luminous landscapes (https://luminous-landscape.com/wp-content/uploads/2008/06/TABLA3.jpg) we can see that at blue wavelengths at 400mm then lens should be able to resolve enough detail for a 16MPix sensor, however at red wavelengths it will not.

 

Sounds like Panasonic have designed a surf lens (not to be used at sunset!)

 



 

All kidding aside, I wonder if this is noticeable in use? 

Quote:Just catching up on the thread. I think perhaps a better way to think about diffraction is there is a point where it starts to visibly "soften" the image, and there is a later point where it is the final limiting factor. Photographers tend to refer to the former, whereas I think Wim is referring to the latter.

 

There are times where it is still advantageous to work well into diffraction limited region. Anyone tried planet imaging? My scope would be, in photographic terms, 2000mm f/10. With barlows (think of them as functioning like teleconverters) I also tried 4000mm f/20, and 6000mm f/30. Of the three, the best results were obtained around f/20, as I was into the noise of my sensor at f/30, and the subject was too small at f/10. The sensor had just over 4 micron pixel pitch if you want to work out an effective MP to compare with photographic sensors, but I think that was in the rough ball park as 18MP APS-C from memory.

Quote:In film photography, we never did worry about this, we just used the Rayleigh criterion, which essentially uses green light with a wavelength of 5120 Angstrom or 512 nm. Green light was chosen because that is what the human eye is very sensitive to.
 
It does indeed make a difference when pixelpeeping, as visible light ranges roughly from 390 to 700 nm, although you could argue it goes from 380 to 750 nm. That is approximately a doubling of wavelength, and halving of resolution, roughly speaking.
 
It will still resolve enough at 400 mm, I can assure you, because the resolution of teh sensor does not actually change, it is the total system resolution that changes because the diffraction limits changes. However, the better a lens is, the closer it gets to the diffraction limit, and certainly at the smaller apertures almost all lenses will be diffraction limited.
 
Do also note that MP limits as discussed are really system MP limits, based on resolution at specific apertures for a lens and sensor system.
 
I'll see if I can work out a few examples to show you what I mean. However, that has to wait till the weekend - away from home for work currently, and limited in what I can do as a result.
 
Kind regards, Wim