Newsgroups: comp.lang.postscript
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: compensating for distortion
Message-ID: <1990Jun4.154728.11348@utzoo.uucp>
Organization: U of Toronto Zoology
References: <90May30.095014edt.18974@me.utoronto.ca> <1990May31.001233.9322@utzoo.uucp> <1289@chinacat.Unicom.COM> <1237@mtxinu.UUCP>
Date: Mon, 4 Jun 90 15:47:28 GMT

In article <1237@mtxinu.UUCP> jaap@mtxinu.UUCP (Jaap Akkerhuis) writes:
>But why are 300dpi printers not 300 in general? At the introduction
>of the Agfa P400 they told me [406 dpi is a nice number in metric].

I can't answer for all the zillion 300dpi models on the market, but I
do know why the HP LaserJet (and LJ+) wasn't 300dpi on the short axis,
and I'm told this applied to many of its brethren.  Resolution on the
long axis was set by the gearing of the mechanical subsystem, but on
the short axis it was set by the video rate from the controller.  The
video rate was ultimately set by a crystal oscillator.  Exactly matching
the long-axis rate required an oddball frequency that would require a
custom part.  However, there is a standard crystal-oscillator frequency
that was *almost* right... so guess what most manufacturers used.

Actually, my measurements indicated that the long-axis resolution was
not exactly 300dpi either, but that might have been due to complications
like the paper stretching slightly on going through the fusing rollers.
-- 
As a user I'll take speed over|     Henry Spencer at U of Toronto Zoology
features any day. -A.Tanenbaum| uunet!attcan!utzoo!henry henry@zoo.toronto.edu