RE: [Leica] why I *don't* want a digital M

[leica@davidmorton.org]

Dante A. Stella wrote:

"The real threat to 35mm film will come with the next generation of
sensors.  If pixel size were to, say, halve, you could halve the frame size
and use much smaller cine-type lenses.  Then you get into f/1.4 and f/2
zooms, things that conventional camera users dream about.  (On that scale,
just about every M-mount lens would be dog slow and huge).  If pixel size
quartered, you would have twice the resolution and half the size."

The chip size has to increase if the resolution is ever going to approach
that of the conventional film process.

For a perfect lens, the minimum spot size on the film (the Airy disk) is a
function of the f number. For green light (ie the centre of the optical
band), the Airy disk diameter is

F         Airy disk        equivalent
number    diameter (mm)    lp/mm
4         0.0045           335
8         0.0089           168
16        0.0179           84
22        0.0246           61

Now clearly at the wider apertures, with real lenses, that theoretical
figure is limited by other aberrations. As you stop down, the resolution
of a well designed lens will approach, and eventually be limited by, the
diffraction effect. Hence the description of a lens as "diffraction
limited".   

The problem is a simple one: you can't scale an optical design to
produce high resolutions from small sensors, because the resolution at the
target (be it film or sensor) is a function only of the f-number, and so
such scaling downwards doesn't work.

- -- 
David Morton
dmorton@journalist.co.uk

"The more opinions you have, the less you see." -- Wim Wenders.