Thanks I wonder if you can help me a little more here with how to read the graphs If we take D76 at 20C then is the case that the top curve indicates the film speed at various development times so to get to 200 the time is just over 7 mins?
How do I work out the Gamma at that development time? Do I just go straight down from the 200 speed? If so this gives me a Gamma of about 0.62 and not 0.58 but I may be making the wrong assumptions about how to read the graphs
The way I do it is to *start* from the gamma I wish to achieve. See example below for Fomadon LQN.
In this example, let's say we wish to aim for a gamma =~ .7 (this is extremely high contrast, way too high for scanning, and I'd imagine also high for wet printing - it's just an example).
Follow the path traced by the red arrow. We start at (1), on the vertical axis on the right. We trace a horizontal path to intersect the gamma curve. At the intersection (2) we'll trace a vertical line to intersect the 's' curve at (3). Starting from (3), a vertical line down towards the horizontal axis will indicate a dev time estimate, whereas a horizontal line towards the vertical axis on the left will indicate the film speed achieved.
For the example above, if we are happy with a gamma =~ .7, we will achieve a speed of 320 and development will require approximately 11 minutes.