04-27-2011, 01:30 AM
[quote name='popo' timestamp='1303720305' post='7890']
But if you take away the practical limitations, then bigger aperture = more potential resolution. Anyone want a sensor capable of out resolving a diffraction limited f/1.4 lens or faster? <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />
I just found it curious that in practice, the "sweet spot" for both formats happened to be around f/4 even with their density differences. Assuming diffraction was the limit when stopping down, intuitively you'd think the FF ones would be much further down from the relative pixel sizes.
[/quote]
Not really. If a lens is best at F/4, it really will, or should be, with any medium behind it, whatever the size. There is a physical limitation to resolution in the first place, about 1/2 the wavelength of light used, and there also is diffraction, which sets in sooner with APS-C than with FF, sure, but that is due to the smaller CoC required to provide an equally sharp picture. At F/4, an excellent lens still has a maximum resolution of around 400 to 450 lp/mm at F/4 for air images. At larger apertures resolution is lower (except with highly specialized and extremely expensive optics) due to teh (im)possibilities of correcting optical faults for edge rays well enough, and at smaller apertures it is less due to diffraction. It is impossible to create lenses which are diffraction limited at larger apertures at a price point the market will bear.
And then there is the medium or sensor - system resolution is defined by the lens formula, which involves both lens resolution and medium (or sensor) resolution, where the latter incorporates CoC, and hence automatically incorporates the effect of diffraction caused by smaller sized mediums. The higher resolution of smaller sized sensors is automatically offset by the larger effect of diffraction, resulting in more or less the same sweet spots at the same apertures, with as only difference more (APS-C) or less (FF) DoF. All this, provided, as mentioned above, that the AA-filter does not have an effect, i.e. flatten the MTF curve.
BTW, I'd love a sensor capable of resolving about the same as an F/1.4 lens which is diffraction limited. However, this sensor would have to be as good as modern large MP FF sensors, the lens would have to be not much bigger and heavier than the current crop of lenses (which i tlikely will be), and my computer for processing images would have to be faster by a factor of 1000-10000 in my guesstimates to process the images as fast per image as my current system does for my smallish 25 to 40 MB images now <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='' />.
I did work things out a few times, and in reality, I'd settle for less. I can easily do 60 cm X 90 cm prints at amazing quality, in colour, now, which would have been impossible in the past with colour film on a similar analog camera.
Kind regards, Wim
But if you take away the practical limitations, then bigger aperture = more potential resolution. Anyone want a sensor capable of out resolving a diffraction limited f/1.4 lens or faster? <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />I just found it curious that in practice, the "sweet spot" for both formats happened to be around f/4 even with their density differences. Assuming diffraction was the limit when stopping down, intuitively you'd think the FF ones would be much further down from the relative pixel sizes.
[/quote]
Not really. If a lens is best at F/4, it really will, or should be, with any medium behind it, whatever the size. There is a physical limitation to resolution in the first place, about 1/2 the wavelength of light used, and there also is diffraction, which sets in sooner with APS-C than with FF, sure, but that is due to the smaller CoC required to provide an equally sharp picture. At F/4, an excellent lens still has a maximum resolution of around 400 to 450 lp/mm at F/4 for air images. At larger apertures resolution is lower (except with highly specialized and extremely expensive optics) due to teh (im)possibilities of correcting optical faults for edge rays well enough, and at smaller apertures it is less due to diffraction. It is impossible to create lenses which are diffraction limited at larger apertures at a price point the market will bear.
And then there is the medium or sensor - system resolution is defined by the lens formula, which involves both lens resolution and medium (or sensor) resolution, where the latter incorporates CoC, and hence automatically incorporates the effect of diffraction caused by smaller sized mediums. The higher resolution of smaller sized sensors is automatically offset by the larger effect of diffraction, resulting in more or less the same sweet spots at the same apertures, with as only difference more (APS-C) or less (FF) DoF. All this, provided, as mentioned above, that the AA-filter does not have an effect, i.e. flatten the MTF curve.
BTW, I'd love a sensor capable of resolving about the same as an F/1.4 lens which is diffraction limited. However, this sensor would have to be as good as modern large MP FF sensors, the lens would have to be not much bigger and heavier than the current crop of lenses (which i tlikely will be), and my computer for processing images would have to be faster by a factor of 1000-10000 in my guesstimates to process the images as fast per image as my current system does for my smallish 25 to 40 MB images now <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />. I did work things out a few times, and in reality, I'd settle for less. I can easily do 60 cm X 90 cm prints at amazing quality, in colour, now, which would have been impossible in the past with colour film on a similar analog camera.
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 ....