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[OM] OM=Japanese Leica???

Subject: [OM] OM=Japanese Leica???
From: "Bov, Frank" <Frank.Bov@xxxxxxxxxxxxx>
Date: Wed, 09 Feb 2000 18:30:50 -0500
Skip, 

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.

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.)

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.

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!

Cheers,
Frank
------------------------------

Date: Wed, 09 Feb 2000 09:21:38 -0500
From: Skip Williams <skipwilliams@xxxxxxxxx>
Subject: Re: Sv: [OM] OM=Japanese Leica???

<snip>

I honestly don't understand the statements that quality is acceptable for 
film, but not for Digital.  The digital CCD's are like groups of little 
pieces of film (or buckets), what difference does it make whether or not 
the light rays are parallel or convergent?  Moden lens design has 
concentrated on minimizing aberrations across a flat film plane.  Forgive 
me, but isn't a CCD flat??!!  If modern lenses can focus onto ultra-fine 
films like K25, 2415, etc and get outstanding results, why not CCD's at 
several times the resolution (worse, not better)?

>The stated reason about NO OM Digital Camera is:  they feel the quality to
be
>obtained from using interchangeable lenses NOT designed for digital is
greatly
>inferior.  It has to do with how a CCD accepts light input, light rays 
>must ALL
>be parallel since the sensor is like little buckets ( U ).  Nikon and 
>Canon get
>around this by using an adapter plate to make the rays acceptable but 
>sharpness
>suffers at the edges, especially with larger chips.
>Also, interchangeable lenses have some play in the mount, and while some of
>this in acceptable and within tolerance for film, it is not for CCD's.


- -----------------------------------------------
Skip Williams
Westfield, NJ
skipwilliams@xxxxxxxxx
- -----------------------------------------------


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