[Leica] Still more digital Leica

[LRZeitlin@aol.com]

I'm not an optoelectronic engineer but I did stay at a Holiday Inn last 
night. 

Actually I didn't stay at the Holiday Inn but I had a couple of drinks at a 
bar nearby with some friends who are real optical engineers from IBM's Yorktown 
Heights Research Lab. We were lamenting the rain induced cancellation of the 
Labor Day sailing regatta in the nearby Hudson River. After a couple of sips 
of a scotch spelled without an L, I posed the digital Leica M question. 
Specifically, could conventional lenses with a short back focus work with a full 
sized CCD sensor. The answer was the same as suggested by the nay sayers on the 
LUG - probably not.  But - and there is always a "but" in discussions with 
engineers - if enough time and money were made available, a digital Leica M could 
be made to work. Here are a couple of the brainstorming suggestions that I 
remember:

Correction plate - a strong planoconcave correction plate in contact with the 
full sized sensor might be the least expensive but it would require 
considerable design work and would not perform optimally with all lenses. The grazing 
angle of a 50 mm lens (back focus about 30 mm) is about 33 degrees at the 
corners of the image frame. The Kodak KAI-110000 sensor requires an angle no 
greater than 15 degrees. Thus the plate would have to deflect light to the vertical 
by 18 to 20 degrees at the corners decreasing to zero degrees at the center. 
For lenses shorter than 50 mm, the corner deflection angle would have to be 
greater, longer lenses would require less deflection. A fixed correction plate 
would work best for only one focal length. One suggestion was to supply 
alternate plates for specific lens ranges, another was to use a single plate and 
correct for light fall off by software, the frame actuator triggering the right 
software mode. An alternative suggestion to the planoconcave correction plate was 
a fresnel lens with groove artifacts removed by software. These guys work for 
IBM, remember. After exposure correction for light falloff is an old and 
venerable photographic technique. A rotating center stop was used for the Hypergon 
wide angle lens and I used to use a graduated neutral density filter in the 
filter carrier of my Bessler enlarger to counteract decreased edge illumination 
with a Canon 19 mm lens. Software would be easier.

Image compressors - If we are not wedded to the concept of a full sized CCD 
and are willing to use a smaller sensor, albeit one with a high megapixel 
count, the easiest approach would be to just use the center 1/2 to 2/3 of the 
image. This is a no brainer optoelectrically. It just converts the Leica into a 
Canon D10 without a reflex viewer. When I opined that many Leica users were wide 
angle fanatics and would object to a change in apparent focal length of their 
lenses, several suggestions for image compression that would give the full 
field of view were offered. The first of these was a fiber optic corrector plate. 
Imagine a fiber optic bundle the size of a 35 mm frame. Now heat and draw one 
end of the bundle out until it is the size of a smaller CCD sensor and 
optically fix it to the sensor. Any image formed on the large end will be reproduced 
in smaller size at the smaller end where it is picked by the reduced size 
sensor. The large end of the bundle could be ground to minimize grazing angle and 
fall off effects and the result might be more even illumination than with 
film. The fiber bundle could be bent around from the inspection port area to the 
baseplate electronics bay. Artifacts and misplaced fibers would be rectified 
by software. Marty Forscher used the fiber optic bundle technique in the very 
first electronic cameras 30 years ago.

Relay lens - The aerial image of any Leica lens could be picked up at the 
film plane and directed by a relay lens to a sensor of any size. The optical 
twists and turns this requires are best left to your imagination.

Afocal lens attachments - A teleconverter type attachment inserted between 
the prime lens and the camera body could be used to increase the back focus to 
the point where a full sized sensor would be practical. Of course this would 
increase the apparent focal length, so an afocal wide angle attachment on the 
front of the lens could be used to decrease focal length to keep the status quo. 
Whether this would still be a Leica lens is another story.

Our booze induced conclusion is that a digital Leica COULD be made given 
enough engineering talent and money. Whether Leica has enough of either is open to 
question. But there is no doubt that a digital camera that uses Leica lenses 
is within the realm of possibility.

Larry Z
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