opticsCreate

 Create an optics structure

   optics = opticsCreate(opticsType,varargin)

 The optics structure contains a variety of parameters,
 such as f-number  and focal length.

 Optics structures do not contain a spectrum structure.  Rather this is
 stored in the optical image that also holds the optics information.

 For diffraction-limited optics, the only parameter that matters really is
 the f-number.  The names of the standard types end up producing a variety
 of sizes that are only loosely connected to the names.

      {'default', standard (1/4-inch)'}
      {'standard (1/3-inch)'}
      {'standard (1/2-inch)'}
      {'standard (2/3-inch)'}
      {'standard (1-inch)'}
         
 There is one special case, human optics.  This creates an optics
 structure with human OTF data.

      {'human'}            % Uses Marimont and Wandell (Hopkins) method
      {'Ijspeert'}         % Ijspeert OTF (Not yet implemented)

 Example:
   optics = opticsCreate('standard (1/4-inch)');
   optics = opticsCreate('standard (1-inch)');

   optics = opticsCreate('human');        % 3mm diameter is default
   optics = opticsCreate('human',0.002);  % 4 mm diameter

 Copyright ImagEval Consultants, LLC, 2003.