Digital BW, The Print

In analytical chemistry the difference between a colorimeter and a 
spectrophotometer is basically in the method of producing the 
"monochromatic" light source used for measurement.  A colorimeter 
typically uses filters although some are now using arrays of LED's and 
produce a narrow band of wavelengths rather than strictly monochromatic 
wave lengths.  A spectrophotometer is capable of producing a spectrum 
of distinct  monochromatic wavelengths and typically uses a diffusion 
grating and a series of pre-filters . Some older spectrophotometers 
used prisms rather than gratings. The X-Rite 810 etc would fit the 
category of colorimeter. Calling them densitometers simply means they 
can do the conversion from percent transmission, %T,  or percent 
reflectance,  %R to optical density, O.D., D,  (mathematically, D = 2 - 
log10  % T)  internally so that they can  output  a linear rather than 
a logarithmic result.

John Bernard Henry's "Controls in Black and White Photography, 2nd 
edition" has a good discussion of densitometry on pages 46-54. It was 
written before the digital age but is still very relevant and if you 
are really into the guts of B&W photography particularly with film a 
must have in my view.

Roger

On Sep 26, 2004, at 11:30 AM, Paul D. DeRocco wrote:



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