02-29-2012, 12:50 PM
Hi Serkan,
In principle, one will always be able to see resolution dropping after the sweet spot of a lens, resolution wise, for the simple reason that diffraction is always active. And do note that system resolution is always lower than the lowest common denominator of both lens resolution and sensor resolution. The question really is when does this become relevant?
In my view, it only becomes relevant when there is no longer gain to be had from stopping down to increase DoF, due to the fact that diffraction causes the image to be too mushy. Generally speaking that is aorund F/18 for FF, and F/13 for APS-C, but this does vary from lens to lens, and shooting distance to shooting distance.
The reason for this is that some lenses have better contrast, and appear to be sharper as a result, than less contrasty, and with regard to shooting distance, it isn't always necessary to have the highest resolution but rather DoF in. e.g. macro shots. When getting closer DoF tends to get so thin that every bit of DoF helps.
Sure, we are losing resolution from the lens diffraction limit onwards, and when we get to the sensor diffraction limit it seems to increase even more, theoretically anyway. However, we should keep in mind that the best amateurs only got 20-40 lp/mm at best from colour negative film, and pros only about 60 lp/mm. This is something many people either don't know, or forget, when pixel peeping test charts, or looking at diffraction limits. In short, there are gains and there are losses; the question really is which one is more important. It is a matter of balance, IMO, IOW, try to get the best possible under the circumstances, and that measn not necessarily going for the highest resolution possible.
Besides this, digital images tend to respond extremely well to judicious sharpening techniques, so even from a slightly mushy picture, or from lightly mushy details, one can still extract quite a bit more if necessary, as I did show in a thread here several months ago.
AFAIAC, the values obtained based on my calculations, only help to understand how the tools work, so that we may know what to expect. And that, IMO, only helps in making specific decisions on how to shoot, how to approach a subject, and make the best of it, not just under the circumstances, but also how to use this.
This also means one needs to experiment within these parameters, to experience the differences, in order to know what to expect. This is not only true for resolution characteristics of a specific body and a specific lens at a range of f-stops, but obviously includes the effect of iso (and noise), and the more often looked at exposure combinations, of shutter speed, aperture and DoF - it doesn't end there however. Similarly, one needs to include processing/developing techniques, and printing techniques (whether that is for display on a monitor or on paper).
Just to show resolution is not the be all and end all, I'd like to show with a photograph that is all mush, but which was first place in a small competition regardless:
![[Image: d_room03.jpg]](http://www.lumifer.com/fs/d_room03.jpg)
Shot with a G10, at 1600 iso, and deliberately underexposed another two stops (by exposing for the bright lights), processed to represent what the eyes could see. This in B&W because the noise was awful, and because the human brain tends to record in luminosity rather than colour anyway when it gets really dark. Furthermore, I knew what to expect from a grain POV, and used it here deliberately.
Resolution? Almost non-existent. IMO very moody, however, and it does convey this, for me anyway. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.
In short, resolution is not the be all and end all, but what counts is how we use what is available, under the specific circumstances. And yes, that also means that the Rayleigh criterion is more useful, as we don't look at things in a binary fashion, which MTF-50 represents, but on a more gradual tone scale, and that is Rayleigh - which works extremely well for printing and displaying, BTW, which is what is was selected for in the in the first place, and which is still valid and still works right until this day.
Kind regards, Wim
In principle, one will always be able to see resolution dropping after the sweet spot of a lens, resolution wise, for the simple reason that diffraction is always active. And do note that system resolution is always lower than the lowest common denominator of both lens resolution and sensor resolution. The question really is when does this become relevant?
In my view, it only becomes relevant when there is no longer gain to be had from stopping down to increase DoF, due to the fact that diffraction causes the image to be too mushy. Generally speaking that is aorund F/18 for FF, and F/13 for APS-C, but this does vary from lens to lens, and shooting distance to shooting distance.
The reason for this is that some lenses have better contrast, and appear to be sharper as a result, than less contrasty, and with regard to shooting distance, it isn't always necessary to have the highest resolution but rather DoF in. e.g. macro shots. When getting closer DoF tends to get so thin that every bit of DoF helps.
Sure, we are losing resolution from the lens diffraction limit onwards, and when we get to the sensor diffraction limit it seems to increase even more, theoretically anyway. However, we should keep in mind that the best amateurs only got 20-40 lp/mm at best from colour negative film, and pros only about 60 lp/mm. This is something many people either don't know, or forget, when pixel peeping test charts, or looking at diffraction limits. In short, there are gains and there are losses; the question really is which one is more important. It is a matter of balance, IMO, IOW, try to get the best possible under the circumstances, and that measn not necessarily going for the highest resolution possible.
Besides this, digital images tend to respond extremely well to judicious sharpening techniques, so even from a slightly mushy picture, or from lightly mushy details, one can still extract quite a bit more if necessary, as I did show in a thread here several months ago.
AFAIAC, the values obtained based on my calculations, only help to understand how the tools work, so that we may know what to expect. And that, IMO, only helps in making specific decisions on how to shoot, how to approach a subject, and make the best of it, not just under the circumstances, but also how to use this.
This also means one needs to experiment within these parameters, to experience the differences, in order to know what to expect. This is not only true for resolution characteristics of a specific body and a specific lens at a range of f-stops, but obviously includes the effect of iso (and noise), and the more often looked at exposure combinations, of shutter speed, aperture and DoF - it doesn't end there however. Similarly, one needs to include processing/developing techniques, and printing techniques (whether that is for display on a monitor or on paper).
Just to show resolution is not the be all and end all, I'd like to show with a photograph that is all mush, but which was first place in a small competition regardless:
Shot with a G10, at 1600 iso, and deliberately underexposed another two stops (by exposing for the bright lights), processed to represent what the eyes could see. This in B&W because the noise was awful, and because the human brain tends to record in luminosity rather than colour anyway when it gets really dark. Furthermore, I knew what to expect from a grain POV, and used it here deliberately.
Resolution? Almost non-existent. IMO very moody, however, and it does convey this, for me anyway. <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />.In short, resolution is not the be all and end all, but what counts is how we use what is available, under the specific circumstances. And yes, that also means that the Rayleigh criterion is more useful, as we don't look at things in a binary fashion, which MTF-50 represents, but on a more gradual tone scale, and that is Rayleigh - which works extremely well for printing and displaying, BTW, which is what is was selected for in the in the first place, and which is still valid and still works right until this day.
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 ....