Response to Densitometer

The enlarger baseboard method is a good idea......but it's only going to give a very rough and ready result compared to a true densitometer. A densitometer should have a collimated optical system that will look at a precise area of the film with a known measuring angle. Projecting an image onto a sensor of wide reception angle will lead to all sorts of errors. The sensitvity will change, depending where on the baseboard the measurement is taken, for two reasons. The first is the Cosine to the fourth power law which will diminish the brightness away from the optical axis and secondly the sensor will be looking obliquely at the light rays. All this is assuming that the enlarger has perfectly even illumination to start with. So unless you fix the position of the sensor on the optical axis fairly accurately, and in some way move the negative around, then the method has quite limited application. Even then, stray light from other areas of the negative is probably going to upset the result, unless you restrict the sensor angle, say with a long blackened tube. Even then one tenth of a stop is a very optimistic estimate of accuracy.

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