Archived posting to the Leica Users Group, 2001/11/06

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Subject: [Leica] digit stuff for those interested
From: Jim Brick <jim@brick.org>
Date: Tue, 06 Nov 2001 08:32:40 -0800

I was told, off line, the following:

"Fact is, your bringing up digital 4x5 lenses, when talking about a Leica, is
just ludicrous and you should know it."

Since I wrote a response, I decided to share it with the group.

The parallel is that the "film" 4x5 lenses are too sharp, their MTF is too 
high for digital sensors, just like MTF of Leica lenses is too high for 
digital sensors. So Schneider (and others) designed a set of lenses with a 
MTF that is matched to digital sensor spacing. And wrote a white paper 
explaining the facts and why they had to do this. Which is why Leica will 
not mount an M lens on a digital camera. They have designed new lenses for 
their partnered (Panasonic) cameras. The Canon and Nikon SLR lenses that 
are used on their respective cameras are not redesigned, but the cameras 
contain low-pass filters to "dumb down" the lenses before the image gets to 
the sensor.

The bottom line is that all lenses are equalized by digital sensors. A 
leica lens is no better or worse than a Sony or Olympus or whatever lens. 
The things we buy Leica lenses for are lost in the digits. In film, a 1 
micron square silver halide grain contains 20 Billion silver halide 
molecules, each capable of being hit (exposed) by a photon. It only 
requires three being hit to produce a developable speck. A digital sensor 
pixel (the minimum recording spot) is 5 microns square (25 sq. microns vs 1 
sq micron) and will ultimately report a light level of 0-255 (256 levels) 
for this whole vast area of 25 sq. microns. This is why Leica lenses out 
perform most other lenses on film, but are no better than anything else on 
pixels. And why film can record deep shadows and bright highlights in the 
same scene. Digital sensors cannot. All fine detail (Leica's strong point) 
is completely lost. Digital cameras are digital cameras. Their integration 
into a film camera body by Canon, Nikon, Kodak, & Fuji is simply to give 
professional photographers a known base to start from. The professional 
level digital cameras from Olympus and others that don't look like 
traditional SLR's and have non-interchangeable zoom lenses produce 
photographs equal in every way to the SLR interchangeable lens cameras. 
They just aren't "familiar" to the pro photographer.

Astro photographers have the same problem. But instead of dumbing down the 
lens, they shift the sensor half a pixel in four quadrants, take four 
exposures, and then analyze the result with software to pick up points that 
fall in between pixels and to differentiate double stars from single large 
objects. A static CCD sensor cannot record these (and other) phenomenon. 
And without either dumbing down the lens MTF or taking multiple exposures 
and processing the results via software, serious aliasing occurs that is 
not fixable with software without producing other artifacts. None of these 
problems occur using film. But film has to be processed and scanned to get 
the image into a computer for analysis.

Basically, digital cameras are digital cameras. The digital sensor is the 
great equalizer. All lens/camera brands sharing similar sensors and price 
will perform equally. Only the post processing software can make a visual 
difference. Lens performance is completely lost. And it will remain this 
way as long as the 5 micron square pixel is the smallest obtainable.

Jim

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