Different films react differently to light of predominantly one color. This can result in changes in exposure and/or contrast from what is expected. For example, I have found that Tri-X with a #25 red filter requires about 2/3 stop more exposure and less development than my meter indicates when I read through the filter. Different films react differently (T-max needs more development with the #25... go figure).
This possibly has to do with how the film is sensitized and how, for example, the red-sensitive component of the film reacts in comparison to the other components (don't quote me here, I am just guessing at this).
With certain film/filter combinations it is not unusual to have to apply a "fudge factor" to the manufacturers suggestion. As mentioned above, I meter through the filter and then apply my personal compensation.
If you can truly narrow the exposure problem you are having to a particular film/filter combination, then simply test to find what compensation is necessary for that particular situation. Many just give more exposure when in doubt; a safe choice with B&W negative materials, others have a more refined set of compensations. In my experience, with weaker filters and in "normal" lighting conditions, little or no compensation is necessary. With stronger filters (red, green, blue, cyan...), some adjustment is necessary from my meter readings.
I have commented on this more extensively in a couple of other threads about metering through filters.
Best,
Doremus Scudder
www.DoremusScudder.com
This possibly has to do with how the film is sensitized and how, for example, the red-sensitive component of the film reacts in comparison to the other components (don't quote me here, I am just guessing at this).
With certain film/filter combinations it is not unusual to have to apply a "fudge factor" to the manufacturers suggestion. As mentioned above, I meter through the filter and then apply my personal compensation.
If you can truly narrow the exposure problem you are having to a particular film/filter combination, then simply test to find what compensation is necessary for that particular situation. Many just give more exposure when in doubt; a safe choice with B&W negative materials, others have a more refined set of compensations. In my experience, with weaker filters and in "normal" lighting conditions, little or no compensation is necessary. With stronger filters (red, green, blue, cyan...), some adjustment is necessary from my meter readings.
I have commented on this more extensively in a couple of other threads about metering through filters.
Best,
Doremus Scudder
www.DoremusScudder.com
