In message <3682EC47.16B8415C.0080BFFB@xxxxxxx>, Pschings@xxxxxxx writes
In a message dated 7/10/2003 1:35:20 PM Eastern Standard Time,
rkm@xxxxxxxxxxxxxxxxxxxx writes:
<snip>
The only problem I couldn't overcome was getting the CCD to the film
plane itself - and I certainly wouldn't recommend taking the CCD out of
the package
What about a fiber optic light pipe, like NPC uses for their Polaroid backs?
You really need to have the fibre bundle intimately mating with the CCD
for that to work, which is quite a demanding optomechanical task. On a
standard CCD, like those you can buy off the shelf, the 2-3mm gap
between the window face and the CCD focal plane would cause too much
loss of resolution to be worth having a high pixel count in the first
place. Even if the light from the fibre ends could be constrained to
10deg cones, which is a tough target to meet, each single point in the
image would subtend around 400um at the focal plane or, in the case of
the Philips chip, about 36pixels in diameter. Since it is more likely
to be a 60-90deg cone, the problem is fairly obvious. You need to buy
the CCD with the fibre bundle fitted instead of the window, and these
are not readily available.
I've read some initial reports from users of the full frame Canon that
they *are* seeing chromatic aberration problems at the corners of the
frame with super wides.
I am sure it can happen, and I did expect to see some - as soon as there
is a finite distance between the colour filter plane and the pixel plane
it becomes inevitable. However, despite my own expectations, I found no
evidence of it with the devices I used and what is pretty close to the
widest angle lens in the OM range. A bit like WMD in Iraq really. :-)
Interestingly, since the Foveon chip relies on the penetration depth of
the light to discriminate colour, rather than a filter, it would not
exhibit chromatic problems at all, irrespective of distance of the
optical vertex from the focal plane.
--
Kennedy
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