Testing films (heeelp, please... :)

Kirk Keyes said:

Sandy - do you then use another test to determine film speed? If you are using absolute values, you can do it directly from a test like the first poster is doing.

I also agree that an enlarger can be fine for speed/absolute testing. Just make sure the exposure time is long enough and that the lamp is voltage stabilised (no cold lights here) to ensure that you are getting consistent exposures.

Click to expand...

Kirk,



Originally, it was a process. First, I followed Phil Davis' method for establishing a personal speed point. This is done with a film (Delta 100) and developer known to produce box emulsion speed. Basiclally, this just allows you to adjust the speed that the Winplotter program indicates, which is basically meaningless until it is calibrated. After you do this once, all of your additional tests of films and developers will indicate a speed relative to the original test film. This is not necessarly the EFS of the film, however, as difference in curve shape may require some slight adjustment upward or downard, in real life, of the indicated speed, but unless you have a film with a really strange curve these adjustments are very small.

In actual practice I have found it very rare that any film/developer combination will have an EFS more than about 1/4 stop from box speed. In my own case, where I develop to a DR of about 1.80 for printing with alternative processes, the actual EFS is nearly always slightly greater than box speed for low and normal contrast scenes. My normal EFS for TMY-400, for example, is 550. That is not how I set my meter, however, because incident metering for B&W film requires some adjustment to EI based on whether you meter in the shadows or highlights.

I can not see that using the absolute values would be any more useful for my purposes than using the relative values based on the calibrated speed point that is in turn validated by field work with a specific printing process.


Sandy

Dont sweat the small stuff...It's all small stuff

Lighten up there Stephen. It's a counterpoint and with humor. You do know humor, yes?

I have a Cosar densitometer, and I can tell you the b+f of almost every film I shoot. But like the other poster who matches a certain zone to a process this is as far as I care to go with it. The irony of all this precision is that from batch to batch, film to paper, the characteristics will change. A certain tolerance can be anticipated with most of the major brands, but with the small European films and papers, this may be so far out of the ballpark to be totally unusable.