Would no the Inverse Square apply as you lower and raise the head above the easel, with other factors of F stop, filters and time being separate calculations, AFTER the physical distance of lens head to easel, is accounted for in percentage of light as intensified or reduced?
Would no the Inverse Square apply as you lower and raise the head above the easel, with other factors of F stop, filters and time being separate calculations, AFTER the physical distance of lens head to easel, is accounted for in percentage of light as intensified or reduced?
Here's the formula: L = 2*log2 (H/(H-M))
L = light-loss, in stops. That is, the meter's reported light-level is L stops higher than what the paper receives.
H = height of lens above paper.
M = height of meter's sensor above paper.
The multiplication by 2 comes from the inverse square law.
Here's a typical example using a 50mm lens for 35mm film: H=14 inches, M=0.9 inches,
L = 2*log2(14/(14-0.9)) = 0.19 stops
Cheers, it's always good to have and know how to make these calculations.
I generally print by eye, after starting out with a meter reading, but being able to take a known good final exposure, say for a 11 x14in. print and to be able to precisely scale up or down is invaluable in the darkroom and production of prints you may want to sell, at different price points.