Re: [Leica] R8/R9 Digital Back announced

[Henning Wulff <henningw@archiphoto.com>]

At 11:29 AM -0400 6/27/03, Aaron Sandler wrote:
>At 10:12 PM 6/26/2003, : "Jim McIntyre" <mcintyre@ca.inter.net> wrote:
>>If the M camera can mount an M lense, and focus on the film plane, then it
>>seems logical that that same film plane can be a digital sensor. Am I in
>>deep space on this?
>
>From what I've read, current digital sensors require the light rays 
>to hit them from an "angle of incidence" that is nearly 
>perpendicular to the sensor.  Film, on the other hand, can accept 
>light hitting it at quite an oblique angle.  Wide angle rangefinder 
>lenses, being close to the film plane, send much of the (outer 
>portion of the) image to the film/sensor from an oblique angle. 
>Therefore they work for film, but not with current digital sensors. 
>SLR wide angle lenses (which are of retrofocal design, meaning they 
>have elements designed to bend the light rays back into being mostly 
>parallel with each other in order that the rays of interest still 
>all hit the film after travelling the additional distance to 
>accommodate the mirror) send all of their image to the film/sensor 
>at a pretty-close-to perpendicular angle of incidence.  Therefore 
>they work for film and current digital sensors.  Anyway, that's my 
>understanding.
>
>For this reason it seems folks are pretty down on the possibilities 
>of using M lenses with digital capture, at least without some kludgy 
>retrofocus add-on that would degrade image quality, make the system 
>much larger, and generally mess up most of the advantages of M 
>lenses.  Recent messages haven't actually used the word 
>"impossible," but that's the feeling that seems to be conveyed.
>
>However, it seems to me that the inability of current sensors to 
>capture oblique light doesn't mean future sensors won't be able to. 
>Plenty of "impossible" things have been accomplished.  Ok, so it 
>might be another decade until the right sensor is made...but I, for 
>one, can wait.  I just hope someone bothers to do it.

That pretty much covers it; although, once again, it's all in the archives :-).

M wide and even the 50 lenses have very oblique rays in the corners, 
so even digital sensors that are half frame can't handle the light 
that comes from these lenses.

One of the problems that has been noted with 'film' lenses on the 
Canon 1Ds is that colour fringing has shown up in the corners with 
much greater apparent severity than on film, purportedly bolstering 
the argument that the 1Ds needs 'higher quality' glass than film 
cameras. This is due to three reasons as far as I can tell; one, the 
oblique ray issue, and: two, the fact that the light rays get 
'digitized', so that even minor fringing can cause adjacent pixels 
(or Bayer cells) to register vastly different colours and: three, 
that the sensors in most digital cameras, but particularly full fram 
sensors, need little 'lenses' to be able to handle any oblique rays 
whatsoever. These cause some further chromatic problems at light 
strikes them obliquely. Analogue (film) sensors provide a smooth 
transition and doesn't show the fringing that all lenses produce as 
easily.

Have a look at a schematic lens design for the new Olympus 4/3 camera:

http://www.steves-digicams.com/2003_reviews/e1_pg2.html

about 2/3 of the way down the page. See the light rays at the rear of 
the lens. That is what Olympus considers ideal. M lenses are about as 
far from that as anything made. The designs that allow outstanding 
lenses such as the 21/2.8 ASPH kills those same lenses for present 
digital image sensors.

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    *            Henning J. Wulff
   /|\      Wulff Photography & Design
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