Archived posting to the Leica Users Group, 1998/08/05

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Subject: Re: [Leica] Slide or drum this is the question
From: Alexey Merz <>
Date: Wed, 05 Aug 1998 12:01:05 +0100

John Chapman wrote: 
> Hi Luggers,
> Alex Merz wrote that dynamic range was more important than resolution
> per se. Dynamic range is completely dependent on the resolution you scan
> at that is a given.
> After that other variables are introduced such as the tonal curve of the
> driver software
> and the file format in which the scanned image is saved in.

The reason that I emphasize dynamic range over resolution is that
for electronic publication, resolution will be much worse than in
ink, dye, or Ag-emulsion output. But with a good monitor, the 
dynamic range of displayed values can be MUCH greater than with 
the above output technologies. Even cheap scanners give greater
(nominal) resolution than your screen can conveniently display, 
but cheap units will not *begin* to extract the shadow detail 
from a typical 35mm transparency.

If you're scanning negatives - especially thin, color ones - this 
matters a lot less (and anyhow, thin negatives are sharper!).

While high resolution will improve dynamic range for very small areas of
highlight or shadow, dynamic range is NOT solely a function of resolution, 
and the Dmax for a given detection system is not resolution dependant.

This is an issue that we confront all the time in biological 
fluorescence microscopy, where a sensitive detector will allow us 
to visualise structures that are substantially (1-2 orders of magnitude)
smaller than the theoretical resolution limit, and where we must often 
balance detection sensitivity, spatial resolution, and temporal 
resolution (frames/sec). At a given temporal resolution, increases
in spatial resolution often mandate a DECREASE in dynamic range.

On topic, our best microscope is a laser scanning confocal unit 
manufactured by Leica, and with it we routinely approach the theoretical
limits of optical resolution (~100 nm point resolution). It's a great
instrument with superlative optics, though the UI of the driver 
software is truly awful...
Alexey Merz | URL: | email:
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