gideon swart |
film rating ive heard many a pro photographer talking about shooting on 100 asa,but rating it 200 asa or pushing it one stop at the lab.what is the significance of that and how many stops can you push. if I shoot on 10-0 asa and set my cam to say 400 asa,what exactly happens with the neg? regards. the black G.
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John A. Lind |
Hi, You have the terminology correct; it's called pushing the film. Not all films can be pushed very well; most of the ones that can are professional films. You need to look at the data sheets for each film; they can be found on the Kodak, Fuji and Agfa web sites. The data sheet will state whether the film can be pushed or not, how many stops it can be pushed, and if so, how its processing must be modified depending on how much it is pushed. Your example of shooting an ISO 100 film at EI 400 is pushing it two stops. [BTW: the opposite . . . shooting a film at a slower speed than its rating . . . is called "pulling" the film.] When you push a film, you are deliberately underexposing it. You need to do this for the entire roll as the film processing must be modified. When you take it to the lab, you must ask for "push processing" and tell the lab how many stops you pushed the film. Most consumer labs will not know what you are talking about, or if they do, they still cannot process it for you. Usually, only professional labs can perform push processing, and you will pay extra for it compared to normal processing. Your film must be handled and processed separately from other films that were not pushed. Typically contrast and graininess increases with pushing a film compared to shooting it at its rated speed. With some films, it increases dramatically. Therefore, it is wise to look at all the faster speed ratings for a family of films to see if pushing a slower speed will result in greater granularity than simply using one rated at the higher speed you want. Regardless of what you find regarding grainularity effects, expect increased contrast. -- John
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John A. Lind |
Some additional information about some films amenable to being pushed and push processing: 1. Color negative films: a. Kodak Supra 400: b. Kodak Supra 800: c. Kodak Royal Gold 1000: 2. Transparency (slide) films: a. Kodachrome 200 (KL): b. Kodak Ektachrome P1600 (EPH): NOTE: Any of these films _can_ be pushed to intermediate EI's between those given by Kodak, however the EI's given are the recommended ones for pushing the film. I can only presume that these are EI's for which pushing the film works better. They are also the EI's for which Kodak gives specific instructions in their data sheets for push processing it. Any other EI would require estimating processing times and temperatures by interpolation from the data in their tables. -- John
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