Re: [Leica] Re: f 1.0/21 ... 1.0/35

["Dan Post" <dwpost@email.msn.com>]

I was trying to go to sleep- hence the late hour of this posting, but I kept
thinking about the problem of light fall off.
Then it struck me. I was taught that the image of a '50mm' lens focused at
infinity is the same size as the image formed by a pinhole 50mm from the
film plane. The compound lens acts the same way, even though the optical
center changes during focusing. If one imagines a line through the axis of
the pinhole, to the center of the film, and that the visual field of the
pinhole is illuminated evenly, then the light from the visual field will
form a 'cone' of light from the pinhole to the film.
If you further imagine that the light striking the film on the axis,
directly behind the pinhole, has an intensity of, say, one or unity, then
the light decreases as you move away from the axis as a function of the
cosine of the angle from the axis. This, of course, holds strictly if the
film plane is curved so that the distance from the center of the pinhole is
the same at the center of the film as it is at the edge. However, the film
is flat so the edges have a reduced illumination, not only due to the cosine
rule, but the law of inverse squares. It seems that the light fall off will
ALWAYS be greater in a wide angled lens from this simple fact.
Now what surprises me is that one can get such good pictures from wide angle
lenses, which must be a testament somewhat to the latitude of film.
Now I'm going to bed! I got this off my mind! Thanks for listening
Dan
- -----Original Message-----
From: Alfred Breull <puma@hannover.sgh-net.de>
To: leica-users@mejac.palo-alto.ca.us <leica-users@mejac.palo-alto.ca.us>
Date: Wednesday, December 17, 1997 4:12 PM
Subject: [Leica] Re: f 1.0/21 ... 1.0/35

>I'd feel it dfficult to construct a symmetrical i.e. f 1.0/21 mm
>or f 1.0/35 lens - since there is not enough space for the backlens
>(I suppose). And a retro would need even more (front) glass than
>the Noctilux (I guess).
>
>Additionaly, there should be severe problems to bring the light
>into the corners of the pix.
>
>Alf
>-----------------------------------------------------------------
>At 11:20 17.12.1997 -0500, Peterson_Art@hq.navsea.navy.mil wrote:
> With any
>>     given maximum aperture, is not a 35mm lens smaller and more
convenient
>>     that a 50mm or 58mm lens for the same camera, and so would not a
small
>>     (relatively) and convenient 35mm f/1 Noctilux M lens be far
preferable
>>     to a larger, heavier, and more conspicuous 50mm f/1 Noctilux?
>
>