The filmís characteristic curve is a representation of how the film responds to a range of sensitometric exposures under specific processing conditions. Itís a picture of the film. I like to think of camera exposure as being superimposed on the film curve, and while the camera exposure can move around the curve, the film curve itself doesnít change. This approach helps me distinguish between the sensitometric exposure and the camera exposure.
There are a couple of ways to think about how the camera exposure falls on the characteristic curve. One is to have an exposure range that has one of itís points falling on a target density like in the first example.
FIlm Curve 30 intervals.jpg
Another way is to use the actual log-H values determined from the sensitometric exposure and link them to the actual camera exposure. While this method isnít practical for most people, I believe it can be useful just to understand how it works.
First we start with the classic camera exposure equation. This isnít any different than the H = E * t equation except that value for E comes from itís own equation. The explanation is an excerpt from a K-factor thread.
Lg can be determined using the exposure meter calibration equation. Please note the value of Eg is 8.11. Rounded this becomes 8 which is the exposure constant usually referred to as ďPĒ. This is the same constant that has the 10X ratio with the film speed constant of 0.8.
Last edited by Stephen Benskin; 05-12-2013 at 03:50 AM. Click to view previous post history.