Why pull-process your film?

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I know that pushing a film gives you more speed, more room to play with apertures and more grain, but why would you want to shoot a tri-x 400 roll at 100 iso, rather than buy a 125 iso, 50 iso or other film, or a t-max 3200 at 400 iso? I'm going to try it but wondered what sort of effect people look for when they do this. Cheers Greg

-- Greg Brosnan (gbrosnan@infosel.net.mx), May 07, 1999

Answers

Pull processing is typically used in the Zone System to enable you to reduce the overall contrast of negative.
The object is to increase the exposure, in effect giving the shadow areas an increase in exposure, while reducing the development, giving the highlights less development. (this is a very basic outline of the concept)Theoretically what you end up with is a lower contrast negative that has better shadow detail, but that typically in my experience, exhibits lack luster high values. That being said I would stick to a 100 asa film and not pull a faster film. Experiment and see for yourself, that's half of the fun anyway!

-- Marv (mthompson@clinton.net), May 07, 1999.

A high contrast scene shot on asa 400 film and processed normally will yield a high contrast and difficult to print negative. A high contrast scene shot on 50 asa film will result in a high contrast and difficult to print negative. In other words no difference. Oh oh. :-)
Reducing developement of either of those films, however, will REDUCE the contrast and make the negatives easier to print. Unlike push processing where you set the meter for a higher speed, normally film rating isn't adjusted for pull processing. To do so would increase the contrast even greater by over exposing the film, and that defeats the whole idea of reducing contrast. So 400 speed is shot at 400, and pull processed for contrast reduction. That, by the way, is about half of the zone system in a nutshell.

-- Peter Thoshinsky (camerabug1@msn.com), May 17, 1999.

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You "pull" your film to get lower contrast, which is necessary in very high-contrast scenes. If you have a film with an ISO rating of 400, and expose and develop it for that speed, on a day where there are very distinct shadows, you will have great difficulty making decent prints from the negatives. Your highlights will be blocked up, and while there may be adequate detail in the shadows, the range of densities in the negative will be too great to print it on a normal (grade 2) paper. Using a lower contrast paper won't help much when huge contrast shifts are needed; paper contrast changes work best when fine tuning your print.
If, on the other hand, you give two stops more exposure (in effect cganging the film's ISO rating downward from 400 to 100), and then reduce development, you will have a negative which is much easier to print. If you find that it is bit too low in contrast, you can go up in paper contrast to get the effect you want. Believe me, a slightly flatter negative is much easier to make a decent print from than one which has blocked highlights.
To give an example, I use Ilford HP5 Plus film for most of my personal work. On a sunny day I will rate it at ISO 100, and develop for 5:00 minutes in HC-110(B). If I find myself shooting on an overcast day where there are no distinct shadows, I will rate it at ISO 500, and develop for 7:45. I sometimes use an intermediate fim speed, ISO 160, and develop for 5:45, usually when the light is a bit diffuse, or when I know that I will be moving in and out of shadows.
The times quoted above are what works for me with my developer, thermometer, agitation technique AND the local water supply! Anybody wishing to establish a table of film speeds amd development times will HAVE to make tests!
And, as long as I am on a tear, "pushing" your film does NOT give more real film speed. Film speed is based on shadow detail; if you examine the ANSI Standards for establishing film speeds under laboratory conditions, you will find a rigidly defined set of conditions to find a film's true ANSI speed. One of the conditions is a defined level of contrast. If you "push" film by giving less exposure and more development, you will NOT find any more detail in the shadows. All you will find is an increase in contrast; you shadow detail will DECREASE!
I push my film when I need the extra speed, but there is a real loss of shadow detail, and a jump in contrast. If you can accept a loss of quality in the negative, you will be okay. But there is no real speed increase.

-- Terrence Brennan (tbrennan13@netscape.net), September 10, 1999.

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