09-25-2011, 11:58 AM
[quote name='Brightcolours' timestamp='1316949827' post='11833']
Where d\from do you get that 512 nanometers is used to determine diffraction for general lenses? It sits at the very end of the visible spectrum, basically... very short wave length (blue). Green already diffracts sooner, let alone yellow and red.
e-line (a green, 546.2 nm) was used originally for the early semiconductor production. They used such very narrow bands exactly for the purpose that longer wave lengths of a normal light spectrum diffract a lot sooner, not being able to reach such high resolutions as needed. So I have to doubt that 512nm is used to determine diffraction for normal photographic purposes...
e-line has a resolution limit of 374 lpmm at f4.
A more normal light spectrum has a way lower resolution at f4.
Maybe 512 nm gets used to compare lenses in certain technical applications, but it can not have any significance for normal photography with a light spectrum instead of a monochromatic blue light source... <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/unsure.gif' class='bbc_emoticon' alt=':unsure:' />
[/quote]
This is just generally accepted practice, for the determination of Rayleigh number and diffraction limits.
It certainly has a significance for normal photography, as this is based on a value between blue light and green light, essentially daylight conditions.
BTW, IOW, this is just convention, no more, no less. If you want to calculate specific resolutions for specific wavelengths, that is fine, but in order to compare lens resolution, this is the generally accepted wavelength for comparisons.
If you want to read some more on this subject, and related fields, I'd suggest
[url="http://www.normankoren.com/Tutorials/MTF1A.html#diffraction"]http://www.normankor...tml#diffraction[/url] and other pages there and in links you can find there.
Kind regards, Wim
Where d\from do you get that 512 nanometers is used to determine diffraction for general lenses? It sits at the very end of the visible spectrum, basically... very short wave length (blue). Green already diffracts sooner, let alone yellow and red.
e-line (a green, 546.2 nm) was used originally for the early semiconductor production. They used such very narrow bands exactly for the purpose that longer wave lengths of a normal light spectrum diffract a lot sooner, not being able to reach such high resolutions as needed. So I have to doubt that 512nm is used to determine diffraction for normal photographic purposes...
e-line has a resolution limit of 374 lpmm at f4.
A more normal light spectrum has a way lower resolution at f4.
Maybe 512 nm gets used to compare lenses in certain technical applications, but it can not have any significance for normal photography with a light spectrum instead of a monochromatic blue light source... <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/unsure.gif' class='bbc_emoticon' alt=':unsure:' />
[/quote]
This is just generally accepted practice, for the determination of Rayleigh number and diffraction limits.
It certainly has a significance for normal photography, as this is based on a value between blue light and green light, essentially daylight conditions.
BTW, IOW, this is just convention, no more, no less. If you want to calculate specific resolutions for specific wavelengths, that is fine, but in order to compare lens resolution, this is the generally accepted wavelength for comparisons.
If you want to read some more on this subject, and related fields, I'd suggest
[url="http://www.normankoren.com/Tutorials/MTF1A.html#diffraction"]http://www.normankor...tml#diffraction[/url] and other pages there and in links you can find there.
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 ....