Page 78 - Lighting the Un-lightable 2015

About a year later, I realized that if I could measure - more or less - the difference

between black and white and if I could convert that to a number of F-stops, perhaps

I could find a way to quantify what the camera was seeing. Because the difference

between two F-stops is a known quantity, if I could convert the difference between

black and white to F-stops, I would have a fairly clear idea of what the camera actually

experienced.

I knew that I could easily build a scale that was usable.

Working in Photoshop on a monochrome image, I realized that, in the digital world,

there were 256 shades of gray, black, and white. So, it seemed relatively straight

forward: Absolute black would be zero and absolute white 256. Since there was no

precise way to determine the black or the white in a scene in relationship to absolute

white or black, I knew I would have to rely on experience. That wasn't what I wanted.

But there wasn't - and still isn't - a better option.

One problem remained. I had no idea how to covert the gray scale to F-stops. Because

I knew that the problems we were facing had something to do with the difference

between black and white, subtracting black from white made sense. Through rather

painstaking experimentation, I was able to determine that every 60 points on the gray

scale was one F-stop. In simple terms, if the black in a scene is 10 and the white is 250,

the difference is 240. 240 divided by 60 equals 4.

So, the difference was four F-stops. What did that mean? If every F-stop doubles the

amount of light allowed into the camera, then 4 F-stops is a difference of (((2x2)x2)x2),

or, a difference of 16 times. No wonder the camera couldn't "see" what I see. Over

time, with the addition of remotely triggered flashes, I was able to determine that I

could render the volume of light consistent by getting the difference between black

and white as close to one F-stop as possible. Whenever I did that, the images exploded

with detail, color, texture, and contrast. The difference was stunning.

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