Quote Originally Posted by Steve Smith View Post
Not relevant as we were referring to moving lights, not the focus (well, I was anyway!) and inverse square rule in general. But yes, on an enlarger the re-focussing will affect it a bit. but only because it will also change the coverage so the inverse square rule will still apply.

noit doesn't!!!!
Exposure Height and Exposure Correction Whenever the enlarger head is raised or lowered, and the negative magnification is changed, print exposure must be corrected. In ‘Tables and Templates’, you will find a chart to determine the magnification of your enlargement and another to estimate the exposure compensation required to accommodate a change in enlarger height. Strictly speaking, projected print exposures fail to follow the inverse-square law, but they follow the inverse square of the lens-to-paper distance if the paper reciprocity failure is ignored, in which case, a new theoretical exposure time (t2) is given by: