Archived posting to the Leica Users Group, 2000/11/02

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Subject: [Leica] Retry and missing link (1)
From: imx <imxputs@knoware.nl>
Date: Thu, 02 Nov 2000 17:39:11 +0100

There are a few strands of arguments mixed up after my original post. Let me
try to entangle and clarify them. And I apologize for being partly
resonsible as I was not clear enough, I am afraid.
First the basic point: I stated that in silverbased 35mm photography a
resolution of 40 lines was enough for god quality/handheld imagery. I still
stand firmly behind this statement.
40 lines times 24mm times 40 lines times 36mm equals 1.3 million image
points. For those with a historical archive, we can look at Barnack's
article about why he selected the 24x36mm format. And you will find the
identical reasoning. Barnack arrived at a maximum count of 1 million image
points as the norm for leica photography.
Incidentally 40 lines per mm give you image points 1/40mm small, that is
image points of of 0.025mm.
As we all know the image points on the negative are assumed to be points
with a diameter of 0.03mm (the circle of confusion). And Barnack used the
diameter of the CoC in his calculation. So we may safely state that the 1.3
million image points in a 35mm negative are assumed by the inventor of the
format to be good enough for normal situations.
OF COURSE; current emulsions have much higher resolutions and when we use
200 lines/mm as the optimum (corresponding to the 100 lp/mm of the best
leica lenses), we get a much higher count: 24 x 200 x 36 x 200 = 34.5
million image points.
Back to the proposition. The 1.3 milion image points are 960 x 1440 image
points. By calling them picture elements, some were quick to assume that the
960x1440 grid or matrix of image points is identical to a 960 x 1440 sensor
array (CCD). 
This however is NOT the case. And by identifying my grid of image points
with a small scale CCD of indeed very modest quality, the matter gets very
confusing.
See part 2