Re: Noise levels as a function of pixel size

In article <doclmj$19h2$1@xxxxxxxxxxxxxxxxxx>, Ilya Zakharevich <nospam-abuse@xxxxxxxxx> writes
[A complimentary Cc of this posting was NOT [per weedlist] sent to
Kennedy McEwen
<rkm@xxxxxxxxxxxxxxxxxxxx>], who wrote in article <rBkQPUCobVqDFwSJ@xxxxxxxxxxxxxxxxxxxx>: 
>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.

Do not know what you mean by "exposure control".

Control of exposure, in this case control by aperture, as in a shutter priority metered system.

The optical
resolution limit has nothing to do with f-number of the fully open
lens.

It certainly has, since the maximum theoretical fully open lens is f/0.5, whilst the practical limit is around f/0.7. That doesn't leave much engineering room if the maximum diffraction limited aperture is around f/1, even if the range does go well into the diffraction limit zone to f/2.8. 

However an f/45 lens is simply unable to match the resolution of the
film

I'm not discussing f/45 lenses. I'm discussing *shots*.

As I am. The difference is that I am recognising that f/45 is sub-optimal on 4x5" due to optical constraints, and the aperture is only available because the format itself provides so much overhead that the resolution losses can often be tolerated. This can often be the case since one of the benefits of the larger film format is increased SNR due to the reduced enlargement of the original film to the final image.

 When a shot
made with one type of sensor produces THE SAME result as a shot made
with a smaller sensor.  E.g., the shot made with f/45 aperture on
4x5in is translated to a shot made with f/2.8 aperture on 2/3''
formfactor (the other things [listed in the initial post] being
equal).

Certainly, you will get just as sub-optimal a shot at f/2.8 on the small digital format as you would with 4x5" film at f/45. However there is no advantage to doing this with digital sensors - you might as well have the larger pixels with lower resolution but better SNR in the first place.

The benefit of smaller pixels only becomes worthwhile when you can achieve the equivalent of the 4x5" format at the resolution limit of the optic *and* film, which occurs somewhere around the f/5.6- f/11 region, depending on the film, just as with any format (since diffraction limit at the focal plane is a function of *only* wavelength and f/#). Unfortunately, that translates to a lens aperture of f/0.35 (impossible) to f/0.7 (realisable but expensive). For higher f/#s you might as well be using larger pixels because you will get the same resolution image at the end of the day, a resolution limited by the lens not the pixel size. 

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.


Exactly the opposite.  E.g., on a maximum-resolution settings, a cheap
2/3'' formfactor ZOOM produces similar resolution image as an
expensive PRIME lens for APS formfactor.

And you can keep preaching that, but nobody seriously believes it.

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.


???  Who talks about single aperture?

You effectively are, by requesting a pixel pitch which is so small that it can only be resolved by an ideal lens which has an f/# only marginally greater than the theoretical limit of f/0.5.
--
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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