Archived posting to the Leica Users Group, 2000/10/30

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Subject: RE: [Leica] Film megabytes and some curious contradictions
From: Paul Chefurka <Paul_Chefurka@pmc-sierra.com>
Date: Mon, 30 Oct 2000 13:53:46 -0800

Here's another data point (as we say in the tekbiz).  I have in front of me a heavily enlarged digital print (8x10) made from a small section of a scan of a Provia 100F slide.

The shot was taken handheld with a 135/3.4 Apo-Telyt at 1/1000 about f/5.6.  The scan was done with a Polaroid SS4000 at 4000 ppi.  The enlargement factor of the final print is about 40x.

As luck would have it, the shot includes a couple of bicycles on which the spokes are clearly (and relatively cleanly) visible.  From the width of the spokes in the enlarged image, I'd say that the resolution on the print is about .5 lp/mm - i.e. each spoke appears about 1 mm wide.  At a 40x enlargement, therefore, the film resolution is about 20 lp/mm.  The theoretical resolution of this scanner is 78 lp/mm (4000 ppi / 25.4 / 2) Subjectively the shot is extremely sharp, but it's obvious from looking at it that film grain and residual camera motion are the limiting factors - not the scanner resolution.

To me this lends credence to Erwin's statement that 20 to 40 lp/mm is the figure of merit to use when calculating how much data is required to capture a real-world image.

The SS4000 generates a 55MB file from a slide at 8 bits/channel (110MB at 16 bits/channel).  The fact that this scanner provides almost four times the resolution required to deal with a hand-held 35mm image suggests to me that 20MB is the crossover point for digital capture *of hand-held 35mm  images*.  Beyond that, you have more digital resolution than the film system requires - giving you the potential to record better quality images (or at least higher resolution) with digital sensors than you can with a hand-held camera and film.

All of this tells me that the advent of 16 megapixel sensors is going to be a traumatic moment in many of our lives :-/

Paul