Re: [Leica] Still more digital Leica

["Sonny Carter" <sonc@sonc.com>]

You remembered all that?  You must not have been paying proper attention to
the scotch!


- ----- Original Message ----- 
From: <LRZeitlin@aol.com>
To: <leica-users-digest@mejac.palo-alto.ca.us>
Sent: Tuesday, September 02, 2003 3:42 PM
Subject: [Leica] Still more digital Leica


> 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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