Yes, but the callier effect you are talking about applies to enlarger light source not to densitometer light source. The reason some densitometers have the ability to vary the sampling aperture is so that you can sample a smaller area of the film, not to try to simulate "difuse or colimated" light sources this is very well explained by the late Dr. Henry. Now if you are talking about spectrometry in thin film applications then that is another matter, but then we get into micro meter densitometers which is entirely a different matter.
Originally Posted by Thilo Schmid
One of the best books in this matter is photographic sensitometry by Todd and Zakia, and I will quote " The present United States Standard specifies diffuse measurements, and all commercially available instruments are said by their manufacturers to conform to this standard in terms of results. Consequently, if we wish to make specular density measurements, we must design our own equipment, or modify existing equipment." So even if you wanted to make specular measurments you would have to have a detector that was away from the film, not in contact as all densitometers work presently. trying to simulate density measurements by specular or difuse source is not practical, and since there are no correction factors to convert either way, for all practical purposes diffuse measurements are the rule.