I accept the radius of one wavelength is the theoretical limit in this case.
I don't recall the maths, but it sounds right.
The other effects are either reductions of resolution below the theoretical
limit, or not relevant.
The original point is about how wide you have to make the circle of
probability to ensure that the image is recorded correctly. Widening this
circle is reducing resolution. Or introducing blur if you prefer.
Geometric aberrations (pincushion, barrel etc) are irrelevant, as they apply
equally to all photons destined for the same image point. Blurring
aberrations (coma, spherical etc) are relevant, but equate directly to a
reduction of resolution. It's just that in these cases it's not uniform.
The original point of all this was to say that photographic lenses are
designed as part of a system, which includes the abilities of the image
recorder in the parameters.
We are used to thinking that all limitations (except grain) on our images
are introduced as failings of the lens design. I have tried to show that the
film itself introduces a requirement to limit the lens design, and that in
this requirement is not something which has suddenly appeared with digital
capture devices replacing film. At the end of the day, if you design a
perfect lens, but the perfectly resolved edges are lost in the film as an
"intermediate grey" of lower edge contrast, did the result get better or
worse?
I was also trying to show that the measured level of performance of current
lenses for film is not universally the result of cost - cutting, but that in
addition to a Cost - benefit question and law of diminishing returns etc
(which tends to produce niche products at high cost), there is an "add
cost - reduce benefit" point beyond which no sensible person would go, and
explains the absence of those niche products in our market.
This has produced an accepted "envelope of system performance" in which it
is the film manufacturers who control the right hand edge and the camera
manufacturers who control the costs within the envelope. Since the envelope
is already pretty large, there's plenty of scope for brand differentiation
in there.
Digital changes that in two ways:
Film manufacturers will become radically more selling - price sensitive, and
will stop pushing the right - hand edge of the envelope. After all they are
now competing with "free - at - source" recording.
Camera manufacturers will control the system as a whole, and (starting with
Oly!!!) begin to produce optimised combinations which eventually will
surpass film in ability. When the E5? arrives with the 11Mp sensor, I expect
it to be a quantum leap beyond the C*n*n in the appearance of the images.
Maybe then I'll go digital.
Julian
----- Original Message -----
From: "Joe Gwinn" <joegwinn@xxxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Tuesday, September 23, 2003 3:25 AM
Subject: Re: [OM] Nope, It missed it by few hundred miles
> The ideal lens of geometric optics does that, but no real lens follows
this ideal, for at least two major reasons. First, all practical lenses
suffer from abberations, so even in the geometric theory of image formation,
the light rays don't quite pass through the same mathematical point in
space. Close, a matter of 5 or 10 microns, but not exact. Second, the wave
nature of light prevents focal spots from being much smaller than a
wavelength of light in diameter, about 0.5 micron. Not that any
photographic lens is diffraction-limited, so the abberations dominate.
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