Re: Medium format scanners
Re: Medium format scanners
- Subject: Re: Medium format scanners
- From: Ernst Dinkla <email@hidden>
- Date: Thu, 27 Oct 2005 11:36:26 +0200
The 4990 has a 4800 ppi optical resolution, not 2400. For $599 with
SilverFast Ai software, its one of the best deals out there (for my
purposes anyway). If your scanning 35mm, get a dedicated scanner. If its
127, 120, 6x9, 4x5, up to 8x10, this is a great little scanner. Talking
about negs and transparencies here. You may occasionally have a problem
with a very dense neg, since the Dmax is only 4.0, but it handles all of
my S.E.M. images on Plus-X or FP-4 so far; and these can have very
troublesome highlites. Unfortunately, I'm still scanning and doing a lot
of my graphics in OS 9. (New G5 some day).
David,
The 4990 has a 4800 SPI = sampling rate per inch. The true
optical resolution in PPI has to be measured in tests. That
Epson mixes up the terms in their specs isn't new, almost all
the scanner manufacturers do and it isn't unusual to see even
DPI mentioned in scanner specs or tests.
With (non-matrix) linear CCDs where the wells of the sensor
are packed to one another it is simple to find the sampling
rate when the sensor specs are known:
Horizontal axis: 1 / sensor well pitch in mils x enlarging
factor.
Vertical axis: stepping rate per inch x enlarging factor.
With the right optics and good mechanical components the true
optical resolution could be close to the SPI then, it usually
is lower.
The Microtek Sigma Six sensor and the Epson matrix sensors
however use more rows of linear CCDs shifted to one another by
half a well pitch or 1/3 a well pitch so the well size is
bigger than the pitch. Other scanners use a stepping rate
that's half the well size. In both cases the SPI is 2x or 3x
higher but the resulting PPI will not make a similar jump. On
the other hand this delivers a better Dmax - Dynamic range as
the wells are bigger compared to the higher resolution sensors
with the same total outer dimensions, so it is a sound concept.
I have both the Epson 3200 and the Nikon 8000. Slightly older
models but with the same internal designs. The Nikon specs are
much closer to the actual optical resolution than the Epson
specs. As tested by some German magazines (actually tests by
Dietmar Wueller of Image Engineering). The Epson 3200 scored
1200 PPI despite the much higher Epson specs, the Nikon 8000
was rated something like 3800 PPI. Don't expect of an Epson
4990 that its true optical resolution will be better than what
the Nikon 9000 can deliver. With a lot of work you can bring
it quite close though.
--
Ernst Dinkla
www.pigment-print.com
( unvollendet )
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