Re: Noise levels as a function of pixel size

In article <dob7tk$sd4$1@xxxxxxxxxxxxxxxxxx>, Ilya Zakharevich <nospam-abuse@xxxxxxxxx> writes 
[A complimentary Cc of this posting was NOT [per weedlist] sent to
Kennedy McEwen

I'm not sure where you are pulling the f/# figure from, but assume you
mean f/# divided by N here, since scaling in the direction you describe
would go in opposite direction of diffraction.  So in the case of your
4x5 film coming down to 2/3" format, we get a scaling of f/# divided by
14 (a 2/3" 4:3 sensor has a long side of 9mm, which is 1/14th of the
long side of 4x5").  So an f/2.8 lens would become f/0.2.


Nope.  The maximal f-number of the lens is irrelevant.  What is
important is the actual f-number used for the shot.  So with 16x
scaling f/45 becomes f/2.8.

The maximal f-number is highly relevant, since that is what determines both the exposure control and the optical resolution limits. Both our numbers are similar, just from a different baseline. However an f/45 lens is simply unable to match the resolution of the film - such apertures are used on large format because there is sufficient headroom to accommodate performance losses, but no if absolute resolution is required. A perfect f/45 lens cuts-off at around 40cy/mm, which is only half the resolution of a good colour emulsion, and a lot less than a good monochrome one - if you can get hold of any these days! ;-)

>     g) have the same "quality" of the lens (e.g, measured as quotient
>       of actual MTF of the lens to MTF of diffraction-limited lens)


I agree with the above, however, it falls over at item (f).  This has to
be measured as a true f-number, taking Llamberts law into account
(recall absorbtion and cosines of angle of incidence?).  Accordingly,
the f-number is not f/d (where f is focal length and d is lens
diameter).


True, but as far as we speak of stuff well below f/1, this is not
relevant.  And I do not think diffraction-limited photographic f/1 is
going to be available close in the future (unless for cell-phone
cameras with 2mm sensors ;-).

Yes, and that is my point really - if you shrink pixels any smaller than the smallest currently in common use then the burden on the optical system becomes inordinately expensive and unsustainable as well as limiting photographic scope. Single aperture cameras have existed in the past and no doubt digital variants of them will continue in the future, but they are more toys than cameras.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
.

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