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[OM] How many pixels in a 35mm film image - Pop Photo weighs in

Subject: [OM] How many pixels in a 35mm film image - Pop Photo weighs in
From: Joe Gwinn <joegwinn@xxxxxxxxx>
Date: Mon, 30 Dec 2002 10:16:39 -0500
On page 37 of the January 2003 issue of "Popolar Photography & Imaging" 
magazine (the "& Imaging" part is new) there is a letter to the editor ("Proof: 
John B") where one John B questions Pop Photo's contention that the information 
content of a 35mm frame is 20-30 Mpixels (these will be marketing pixels), 
because he personally gets better photos with digital cameras. One assumes that 
his camera has far fewer mpix, although this isn't stated.  The letter was in 
response to an editorial in the November 2002 issue of Pop Photo.

The Editors' answer more or less recapitulates our computations, albeit with 
less math detail, summarizing that 24 Mpix is for handheld SLR shots, while 30 
Mpix is for "optimal" situations.  All this with ASA 100 color negative and 
slide films and a top-of-the-line 50mm lens set to its optimum aperture, with 
camera on a heavy tripod with remote cable release.  No mention of mirror 
lockup.  Under less rigorous conditions, or with a 35mm point&shoot, one gets 
6-12 Mpix.  

In my analyses, I used 50 line pairs per millimeter as the typical performance 
of lenses, a conservative number, and ended up with 18 Mpix.  Pop Photo instead 
tried to estimate the best that could be done in practice, and got about double 
that.

Assuming that the 30 Mpix is for a camera of 1:2:1 ratio, this is the 
equivalent of 15 million tricolor pixels, and the frame will be about 4743 x 
3162.

In all cases, the color accuracy of digital exceeds that of any film Pop Photo 
has tested.

Pop Photo goes on to conclude that the lack of film grain plus the greater 
color accuracy leads many to choose "digital enlargements" over "film-based 
enlargements".  This part threw me.  Who was talking of enlargement only?  We 
were talking of the relative merits of film and digital cameras, and one could 
read their conclusion to endorse scanning of the negatives, which is not 
supported by their other points.

Perhaps the missing logical step is to note that at current price levels, the 
cheaper route to digital is to use a 35mm film camera and scan the negatives.

Joe Gwinn

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