Quote Originally Posted by Jorge
I hesitate to do this, but this information is wrong and goes against every principle of sensitometry.

The densitometry has nothing to do with the type of light the enlarger uses. Densitometers do not use diffuse or colimated light. all they do is pass a beam of light through a small section of the film and the diference in opacity from the reference beam is detected by a photo sensor. If anything all densitometers are "diffused light" as the light gets scattered by the film.
I beg to differ. The measurement charachteristics is important and is usually indicated with the technical data (and is the reason why you can change the aperture on some densitometer models). The Callier Effect will not change the basic shape of the caracteristics curve (well - there are people, who believe it does), but it will for sure change the grade. This is the reason why you usually have different development times for condensor and diffuse light enlargers. You may, of course, apply arbitrary correction factors in this case. But this would indeed be "against every principle of sensitometry". The Callier Effect depends on light aperture, grain size and grain shape and you will need different correction factors for different types of film/developer combinations. To be exact, you would have to calculate backwards from paper densities to receive the desired negative densities you should tune your development process to.

There is a good document about this availiable under: http://www.gigabitfilm.de/download/callier_effekt.pdf (esp. the second part about the different measurement geometries on transparent targets)
Unfortunately, it is written in German, but some translation program might help.