Re: Noise levels as a function of pixel size
- From: Ilya Zakharevich <nospam-abuse@xxxxxxxxx>
- Date: Fri, 30 Dec 2005 23:47:20 +0000 (UTC)
[A complimentary Cc of this posting was NOT [per weedlist] sent to
Kennedy McEwen
<rkm@xxxxxxxxxxxxxxxxxxxx>], who wrote in article <6i3k3EC6OWtDFw6x@xxxxxxxxxxxxxxxxxxxx>:
> >Kennedy, I was discussing the situation when one particular shot made
> >with a larger sensor produces the same result as one taken with a
> >smaller sensor. Apparently, you are discussing something else;
> >actually, I do not know what. I can't continue until I understand
> >what is the context of your statements...
>
> Since we don't make digital cameras for one particular shot, let alone
> develop entire technologies for it, what you claim to be discussing is
> quite a pointless subject. For what it is worth, I was discussing where
> the technology can go, what is achievable
With all due respect for such high goals, let me note that it does not
make sense to discuss such things without agreement when ONE SHOT made
on one piece of hardware produces the same results as one made on
another hardware. Or should I take this as an agreement with the
scaling laws posted in my message.
> >As I said, maximum NA of a diffraction-limited in-the-air lens I know
> >is 0.93.
> That would have to be pretty high humidity air, since the maximum
> theoretical NA of any lens is 1/n, where n is the refractive index.
Well, n=1 for air, so I do not see any contradiction. Anyway, your
claim is absolutely wrong.
> The correct formula for f/# is 1/(2xNA), so certainly f/0.5 corresponds
> to the maximum numerical aperture.
This formula is no way "correct". However, it is a good approximation
for small NA.
> >Somebody counted (one of Davids?), and 50% of published 4x5in images
> >are made at f/45; this is why I discuss this number.
> Published images do NOT represent the limits of the 4x5" medium - not by
> a long way.
I was not discussing "limits of 4x5in", only "a typical use"; with the
scaling laws I given, it is clear that one cannot reproduce all the
capabilities of 4x5in with less than 9-cameras-in-a-matrix in 2/3"
formfactor. However, the typical usage may be within reach of one camera.
> In short, the benefit of 4x5" film for such publication is NOT the
> resolution of the medium, but its improved SNR over a smaller format.
> Hence the use of a high f/# optic, which is well into diffraction
> limited region compared to the medium at the focal plane (film) is quite
> acceptable for the final application.
AFAIK, the reason for using f/45 is not to decrease the quality of
image and increase inconvenience to the photographer, but to achieve
necessary depth of field.
> >AFAIK, 4x5in-format lenses max the resolution about f/16.
> The aperture at which the ideal lens resolution equals the resolution of
> the film is INDEPENDENT of the focal plane format.
Since different films have different "resolution" (whatever this
means), there is no reason to take film into equation so early.
> from other aberrations can increase the optimum point up to f/11. The
> resolution achievable at f/16 is well below the resolution capability of
> film.
What I was discussing was the resolution of optic, not the film.
> I am not putting words into your mouth. When you ask for a pixel which
> can only be utilised at one practical aperture then you are talking
> about single aperture applications, whether you understand what you are
> saying or not!
You definitely have very different meaning of "utilized" in mind.
Probably, you think also that the body is the most expensive part of a
photography system? Or if film "matches" resolution of f/5.6, it is
also a "single aperture application"?
> >I'm taking about a lens which gives a close-to-diffraction limit
> >performance at f/2.8.
>
> Which is significantly larger than the pixel size you are proposing to
> place at the focal plane. If the lens cannot resolve individual pixels,
Again, you put carriage in front of the horse. With cheap sensors
(probably not yet here in 2006, but very close ahead) - practically
free in 4/3" formfactor and below - it is the sensor which should
extract all the information from the lens, not visa versa.
> I find it incredible that you argue on this subject when you have no
> idea that the lens has to be capable of resolving the pixel pitch to
> make any case whatsoever for small pixels.
This makes absolutely no sense (unless your body is much more
expensive than your lenses). See sampling theorem.
> >maybe you live a world where the camera is more expensive than its
> >lenses, so you want to use only the settings which would extract the
> >maximal resolution from the camera?]
> I live in a world where the performance of the lens can, and often does,
> exceed the capability of the sensor - that is WHY the sensors have to be
> fitted with anti-aliasing filters. Why would anyone buy a sensor which
> no lens could ever achieve its full capability?
The only reason AAF are here is the sensors not yet achieving the
necessary resolution yet.
Hope this helps,
Ilya
.
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