[filmscanners] RE: Film resolution - was: Re: 3 year wait

["Austin Franklin" <darkroom@ix.netcom.com>]

> Austin,
>
> The Fourier series of a square wave consists of the fundamental frequency
> and odd harmonics only.  I don't understand where the '4f' comes
> from.  4x
> sampling won't get the 'amplitude' of the square wave(test pattern) much
> better than Nyquist sampling.

Jonathan,

Of course it will with respect to film scanners.  Draw a black line of width
N on one piece of paper, and a simulated sensor array of 2f, then another
one of 4f.  The sensor array width for 2f will consist of sensors that are
the width of the line, and the 4f array will consist of sensors that are 1/2
the width of the line.

Now, show how your 2f array will give you %100 amplitude detection reliably
(as in, in ALL orientations).  Answer is, it can't!  To get %100 amplitude,
the sensor has to see ONLY the line (yes, it's the opposite, as in
black/white, but it's far easier to draw a black line on white paper), or it
gets degraded amplitude...and to see %100 amplitude for any orientation, one
sensor needs to see ONLY the line in ANY orientation.

Now try that with 3f if you like, you'll still find that it isn't %100
reliable...but 4f gives you %100 reliable amplitude.

Austin

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