At 2/9/00 06:30 PM -0500, you wrote:
I think you've answered your own question - if the light rays are steeply
convergent, they're more likely to hit the side of the bucket and be lost.
Film is a series of thin emulsion layers, with great care taken to get the
light directly to the silver halide grains in each layer with a minimum of
scatter. Film backing and the bottom emulsion layers are designed to
minimize negative effects from light that makes it through these layers, but
there's nothing to prevent detection until then. CCD's are solid state
devices consisting of multiple layers of doped semiconductor material; I
believe the actual sensitive layer is several layers down, and there are
boundaries (walls?) between pixels. The light has to get to the "bottom" of
the bucket to be sensed. If it comes in from too high an angle, it hits the
wall and is lost.
I understand your argument that the photons might "hit" the wall and be
lost, but are you SURE? I'd be surprised if there weren't silicon devices
for gathering as many photons as possible across the CCD's face, otherwise,
you'd have falloff at the edges.
Astronomers have been using CCD's for years, and I've never heard that the
optics required for astronomy were any different. They don't switch
telescopes depending on the detector. In fact, detectors are routinely
swapped out at large observatories, depending on the application. And that
includes emulsions and photographic plates. Sure, they use transfer lenses
to get the image to the imaging plane, but I've never heard that any
shenanigans are necessary to "uncollimate" the light cone?
35mm film is a large-format recording medium compared with most CCD arrays.
A 1:1 perspective is still achieved when the focal length = image area
diagonal, but with a smaller diagonal, lens focal length for a given
application is proportionally smaller. Someone quoted a factor of 4; this
sounds about right. The lens on our Nikon 950 is tiny! (Don't shoot me, it
was my wife's money and she wouldn't buy the comparable Oly.)
Yes you're right. It's the same effect you get with a half frame or APS
camera. A bigger perspective for a smaller focal length. I.e., the
100mm/3.5 Olympus Pen lens is equivalent to about a 150mm OM-system
lens. That's why all the digital cameras and camcorders have smaller focal
lengths than other formats to produce the same image perspective and size.
Finally, since CCD arrays capture a smaller image, the same amount of scene
detail requires a much higher resolution in the aerial image if the CCD is
to record the same amount of information from the scene. This puts quality
requirements on the optics beyond what conventional film can resolve.
I don't agree here. This only means that the CCD's throw away some of the
potential resolving power of the lens because the pixel size is greater
than the capabilities of the optics.
Bottom line: a CCD camera requires a smaller, extremely high quality lens
with optical correction in it's final stages in order to match the speed and
detail rendition of conventional film. Just as a CCD camera lens wouldn't
work on an OM-1, you shouldn't expect your OM-1 lenses to work on the CCD
camera. They're different applications!
If so, that argument would hold that lenses for a Hassleblad could never be
as good as a 35mm lens, because they have to cover a larger format, and I
don't think that the Zeiss and Schneider lenses on a Hassy or Rollei are
inferior.
Why wouldn't a CCD camera lens work on an OM-1? It should produce a nice
circle in the middle of the film, as it's image circle is
smaller. Conversly, I still don't yet see any rational reason or argument
as to why 35mm lenses wouldn't work great on a CCD camera.
For an additional consideration: Leica makes the professional S-1, their
digital studio camera, which will take lenses from the M-series, R-series,
Nikon, Hassleblad, Minolta, and even the OM-system. Help me to understand
THAT rationale if CCD's require "special" lenses.
Once again, I DON'T BUY IT. It's marketing bull
The gauntlet still lays there,
(Sorry to be such a hard-ass on this subject, I just have a low tolerance
for techno-mumbo-jumbo-doubletalk masquerading for a rational, truthful
explanation. I guess it comes from working in the technology and large
system consulting fields for so long. I've pushed my share of
techno-doubletalk, and I've caught a lot of sales types trying to pull the
wool over on me.)
Skip
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Skip Williams
Westfield, NJ
skipwilliams@xxxxxxxxx
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