Archived posting to the Leica Users Group, 2002/08/31
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At 12:18 PM -0700 8/31/02, David Rodgers wrote:
>Henning
>
>> A short back focus is no problem if the sensor size is
>>correspondingly small,
>
>I wouldn't mind an M body with a chip that was smaller than 35x24mm
>if that's what it takes. There'd be a focal length factor, but
>that's not the end of the world. Everyone else has a focal length
>factor. My 15mm Heliar might be more like a 24 or 28. And my 21/2.8
>Elmarit more like a 35. I could live with that. After shooting
>digital for some time (with a P&S G2) I'm beginning to think that
>film is on the way out for 95 percent of all photography. I love
>shooting film and I I was in denial for a long time. But I believe
>now the writing is on the wall.
>
>Dave
I'm not sure what the present maximum acceptance angles are, but the
most problematic lenses are the wideangles, such as the 15 and 21,
which have rear elements and mount protrusions located _just_ far
enough off the film to allow the light meter to read the spot
properly. I wouldn't be surprised if the sensor size has to be a fair
bit smaller than the present ones in SLR's such as the Canon D60 or
Nikon D100. Apparently one of the problems with SLR's that have the
full frame sensors that have been produced the acceptance angle has
been one of the problems, and in SLR lenses the exit pupil on lenses
at worst is about three or four times as far from the film plane as
the exit pupil on the 15 Heliar or 21 Elmarit. This might mean that
the sensor size would force a focal length multiplication factor of
3, which is clearly unacceptable. Who would want an M-Digital which
would still cost a ton of money that would need a 12/5.6 lens to give
you a 36mm equivalent angle of view, and that would turn a 21/2.8
into a 63mm?
Digital P&S cameras have lenses which are designed for the specific
sensor, so can have the correct optical geometry. Also, they do not
nearly produce the same resolution or lack of distortion that we
expect of Leica lenses, which cause some of the problems when they
are put in front of a digital sensor.
Don't take all the above literally, as I am not involved in designing
digital cameras. It's just that these in general are the parameters
that we are dealing with according to various sources, and they make
a lot of sense from a physics/mechanical/optical point of view.
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:henningw@archiphoto.com
|[ ]| http://www.archiphoto.com
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