[quote name='popo' timestamp='1316987504' post='11853']
Using any sampling rate, you can retrieve data from almost any frequency, even those above the Nyquist. For unknown broad spectrum signals, this is a problem of course that aliasing can occur and you can't determine where the apparent signal spectrum is from. However, in the case of the Imatest test, the signal is effectively known and I assume they use that to separate the signals of interest above or below the Nyquist. I further assume this is limited in scope as reducing signal-to-noise would render it unusable if you try to take this too far.
[/quote]
Exactly, and for photographic use, it being a broad spectrum application, I would like to suggest that going above the Nyquist frequency is rather useless in the practice of the type of photography we normally use a camera for. Above the Nyquist frequency, we do not resolve real data in a broad spectrum as used in photography. That is what I was taught at uni anyway.
Is it useful for creating MTF charts for lens tests? I don't know, but personally I have my doubts, I think it is spurious information. However, the Imatest people think it is a useful addition, and they are the experts, I guess.
Kind regards, Wim.
Using any sampling rate, you can retrieve data from almost any frequency, even those above the Nyquist. For unknown broad spectrum signals, this is a problem of course that aliasing can occur and you can't determine where the apparent signal spectrum is from. However, in the case of the Imatest test, the signal is effectively known and I assume they use that to separate the signals of interest above or below the Nyquist. I further assume this is limited in scope as reducing signal-to-noise would render it unusable if you try to take this too far.
[/quote]
Exactly, and for photographic use, it being a broad spectrum application, I would like to suggest that going above the Nyquist frequency is rather useless in the practice of the type of photography we normally use a camera for. Above the Nyquist frequency, we do not resolve real data in a broad spectrum as used in photography. That is what I was taught at uni anyway.
Is it useful for creating MTF charts for lens tests? I don't know, but personally I have my doubts, I think it is spurious information. However, the Imatest people think it is a useful addition, and they are the experts, I guess.
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 ....