Re: Digicam vs. Scanner resolutions

["dickbo" <dickbo@xxxxxxxxxxxxxxx>]

----- Original Message -----
From: "Phil.Lippincott" <phil.lippincott@worldnet.att.net>
To: <scan@leben.com>
Sent: Tuesday, June 11, 2002 4:40 AM
Subject: Re: Digicam vs. Scanner resolutions


> referred to. Drum scanners do not use an optics lens to see or reproduce
images.

Oh really? so why have a lens at all. Lets all use pinhole technology.
Drum scanners do or certainly did use an optic and with two aperatures in
operation at any given time. It might well be that a whole image is not in
focus across it's required area at any given moment in time, but the
analysing spot most certainly must be in focus and before it hits the
Photomultiplier too.

Actually I'll go further than that. Certainly before other techniques became
available de-focus could be used to re-screen an already screened image and
that requied an optical device in order to carry out the function.

What you really mean is that a drum scanners optical device is not used as
the major arbiter of image quality in the way that a camera lens is used,
however optical quality still contributes to the final result on a drum
scanner because if the spot hitting the PM is not sharp it becomes perfectly
possible that at the digitising stage a grey level error may be generated
and most certainly optical USM will be affected.

Now it may well be that you are going to tell me optical USM is no longer
available on modern drum scanners and I will believe you, but it certainly
was the case for all drum scanner manufactured up and including the year
1995.


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