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RE: filmscanners: Scanner resolution (was: BWP seeks scanner)
Here's a related resolution question.
McNamara quotes 60 lp/mm. I arrived at my initial 75 lp/mm by doing a
braindead calculation: 4000/25.4/2. My calculation is obviously optimistic -
I'm assuming that adjacent rows (or columns) of pixels each resolve "1 line".
I would have expected (bit being bits and all that) that any degredation from
that theoretical maximum would have involved a division by 2. That's obvously
not the case with McNamara's number.
So the question is: what factors would conspire to lower the resolution
fractionally like that? The suspects I come up with are:
- CCD bloom
- An interaction between the analog detail on the neg and the discrete CCD
pixels (leading to something like dither if I'm not mistaken)
- System noise
Anyone have any ideas?
From: BHannaford@aol.com [mailto:BHannaford@aol.com]
Sent: Friday, June 15, 2001 1:28 PM
Subject: Re: filmscanners: Scanner resolution (was: BWP seeks scanner)
In a message dated 6/15/01 11:53:29 AM Eastern Daylight Time,
<< After all, 4000 ppi gives a resolution of 75 lp/mm or so, and it takes
pretty remarkable technique to actually get that kind of resolution onto
film. Or is my crude first-approximation assessment incorrect, and we
actually can't resolve detail in the scan at more than half that - say 40
lp/mm with reasonable contrast? Even that level is still sufficient for
prints that appear "sharp" at normal viewing distances.
Paul Chefurka >>
Here is an interesting observation from Michael J. McNamara (PopPhotgraphy
July, p58)at the conclusion of the article on their scanner tests: "...Even
the best 4000 dpi scanners we've tested aren't capable of capturing all the
detail found in a 35mm color original under optimum conditions (tripod,
mirror lockup,etc). In our tests the highest res we've found in a 35mm color
slide or negative is 77 lp/mm. The best 4000 ppi scanner can capture about
60 lp/mm, about 25% lower. But that's perfect, because under normal shooting
conditions (i.e., handheld instead of tripod mounted), 60 lp/mm is about all
you'll ever get from an SLR."