Quote Originally Posted by KenS

When working, I used to do a lot of macro work with small sealed glass bottles or test tubes with bacterial or fungal cultures on their specific growth media.
I would meter with the incident hand-held meter pointing twards the polarized light source. Correct exposure was usually 1.5 stops (plus bellows extension, plus 1 and 1/3 for the on-lens polarizer) open from the light meter reading.

In about 20 years, I rarely found this technique to fail.

Thanks Ken, I'll try this out. I have always wondered a quantified manner in which to measure backlighting with an incident meter--before it was guesstimation (which was pretty close most of the time, but not all of the time).