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RE: filmscanners: Scanner resolution (was: BWP seeks scanner)



OK, I *know* what happens when a very good camera lens does this test--the 
end of the scale turns to mush. Can anyone say what happens when a CCD does 
this? My guess would be "noise," but I frankly don't know and I've never 
seen it done. Any comments? I'm reaching.

Best regards--LRA


>From: Filmscanners@davidmorton.org
>Reply-To: filmscanners@halftone.co.uk
>To: filmscanners@halftone.co.uk
>Subject: RE: filmscanners: Scanner resolution (was: BWP seeks scanner)
>Date: Sat, 16 Jun 2001 00:20:19 +0100
>
>Austin Franklin wrote:
>
>"4000SPI (samples/inch) divided by 25.4 mm/inch = 157.48 samples/mm, which
>means it can always resolve a detail that is (157.48 samples/mm divided by 
>2
>for sampling frequency divided by 2 for line pairs) = 39 lp/mm is the
>minimum resolution that a 4000SPI scanner can resolve.  That is for line
>pairs that are perfectly horizontal or vertical."
>
>Dividing by two *twice* in this calculation is not correct (we've had this
>conversation before).
>
>Nyquist tells us that we must divide the sampling frequency in two to
>calculate the maximum spatial frequency (to allow for one bright line, then
>one dark line). By dividing once "for sampling frequency" and once "for 
>line
>pairs" you're doing the *same correction twice*.
>
>The highest theoretical resolution that a 4000spi scanner can resolve - 
>with
>line pairs that are perfectly horizontal or vertical - is 157.48/2 or 78.7
>lp/mm. Of course various optical and CCD effects can degrade this maximum,
>which is how we get to intermediate figures such as McNamara's 60lp/mm.
>
>--
>David Morton
>dmorton@journalist.co.uk
>
>"The more opinions you have, the less you see." -- Wim Wenders.
>
>
>
>

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