Film speed vs. deep black

[noseoil]

I continue to hear claims about film speed and developers. Some yield full speed, some half speed and some are downright slow. Still a bit confused about film speed as a function of the print values. As an example, I hear that pyrocat is capable of "full speed" in some cases, which may be true, but in general I tend to run things slower, so here is my question.

With Efke 100 and pyrocat, I tend to use asa 32 or 25 for azo contact printing. Granted, this is pretty slow, but I've found that running it faster does not yield fully black edges in the print. With faster speeds, I don't get black edges of film base plus fog, as there is a lighter shade of gray at the film's edge. I've settled on the slower speed in order to get deeper blacks.

My question is, am I missing something here, or is it just a case of contact printing on a specific paper which is subjet to U.V. light, so things are a bit different? Am I just pushing things up to the flat line to take advantage of the film's curve? tim

 

[Jorge]

I get full blacks with Pyrocat HD and printing in pt/pd with full film speed. I suspect you are not giving the film enough development to get a high contrast negative, which is what you need for Azo.

 

[sanking]

Tim,

There are really two issues here. One is a theoretical film speed that would assume a perfectly straight line film and process. Such a combination would be TMY film and the carbon process. But we usually must deal with both films and processes that have distinctive toes and shoulders.

I believe that Jorge is right in suggesting that you are not giving the film enough development to get a high contrast negative, which is what you need for Azo. Also, however, you have to weigh the importance of increasing exposure to push important shadow detail out of the toe and up onto the straight line part of the curve. This is really important with films that have long toes, and TRI-X and Efke 100 are such films. So in essence you have to rate the film with an effective EFS of much lower than what the manufacture recommends in order to obtain good separation in the shadows. But this is a film curve issue, not one of EFS caused by the developer.

What I would suggest in your case is this. Rate Efke at about EFS 50, then either increase time of development with your standard dilution or use the same time with a stronger dilution to get more contrast. Say for example, if your standard is 10 minutes with the 1:1:100 dilution, either increase time to 15 or 20 minutes, or use a stronger dilution, say 3:2:100 or even 5:3:100, with the same time.

Sandy

I continue to hear claims about film speed and developers. Some yield full speed, some half speed and some are downright slow. Still a bit confused about film speed as a function of the print values. As an example, I hear that pyrocat is capable of "full speed" in some cases, which may be true, but in general I tend to run things slower, so here is my question.

With Efke 100 and pyrocat, I tend to use asa 32 or 25 for azo contact printing. Granted, this is pretty slow, but I've found that running it faster does not yield fully black edges in the print. With faster speeds, I don't get black edges of film base plus fog, as there is a lighter shade of gray at the film's edge. I've settled on the slower speed in order to get deeper blacks.

My question is, am I missing something here, or is it just a case of contact printing on a specific paper which is subjet to U.V. light, so things are a bit different? Am I just pushing things up to the flat line to take advantage of the film's curve? tim