push and pull??

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Can you please explain to me what the term push and pull means?

-- Wendy Conti (sun21scrn@aol.com), July 25, 2001


When you push a film you are increasing it's speed from the manufacturer's rating and deliberately underexposing the film. For example: 400 rated film pushed to 800 would underexpose the film by one stop. You would use this method if you were shooting in low light conditions and needed a shutter speed fast enough to allow you to hand hold the camera. Pushing a film also increases its grain and this can be used to create interesting visual effects as well. You do have to make up for the gain in film speed by increasing the development according to how much you push it. Pulling a films speed is just the opposite of pushing. 400 rated film pulled to 200 is overexposed by one stop and hence needs less development.

-- Justin Fullmer (provo.jfullmer@state.ut.us), July 26, 2001.

Film's ISO speed is a property of the film and does not change no matter how you expose or process it. (One might argue some films are more honestly rated by manufacturers than others, but this is another issue.) Pushing films is merely underexposing and boosting the contrast by overdeveloping to make the image printable. As a direct consequence of this, some shadow detail is inadequately exposed to register anything on the film when underexposed, and this loss cannot be salvaged by overdeveloping. Grain increase is a secondary consequence of overdevelopment.

Some developers such as Ilford Microphen and Eastman Kodak T-MAX developers can increase usable speed by about 1/2 stop. This is a boost in true usable speed (but not increase in ISO speed - ISO speed is fixed) and not a push. This is because these developers develop more shadow images than the developer used in ISO standard measurement while contrast and speed point criteria are held fixed. Perhaps you need to find a carefully written tutorial article to learn more detail on this.

There are three things (or possibly more) for each film: (1) ISO speed, (2) effective or usable speed for particular processing, and (3) exposure index actually used for metering and exposure.

(2) can be different from (1) but usually this does not mean push or pull. However, if you choose (3) different from (2) then it is either push or pull.

My personal opinion is that push/pull isn't worth spending time unless you have a very good reason to do. Those techniques were probably more useful when papers didn't come in many grades or extreme grades didn't have equal image quality as grade 2.

-- Ryuji Suzuki (rsuzuki@rs.cncdsl.com), July 26, 2001.

Keep in mind: If there is NOT enough light to properly expose a 400 film, rating it at 800 does not improve the situation. You should probable never change the ISO setting on your camera, but simply be aware of how much you are underexposing your pictures. If it's just 1 stop, a little extra time in the developer will provide a bit more density to the mid tones and high lights. Shadows will not be helped.

-- r (ricardospanks1@yahoo.com), July 26, 2001.

Agree with the posts above. It probably sounds better to say, "I pushed my Tri-X to E.I. 3200!", than "I underexposed my film by 3 stops and lost all the shadow detail and most of the midtones too". There are times when it helps, but you have to understand the tradeoff and be willing to pay the price.

-- Conrad Hoffman (choffman@rpa.net), July 26, 2001.

I've seen this answer to 'pushing' before and it's real hard to comprehend after years of 'push to 3200asa' brain washing! That's much easier to comprehend than 'under exposed by 3 stops and development extended 45% on my normal development time and agitation methods"! 2nd method does tell you more though! :)

-- Nigel Smith (nlandgl@unite.com.au), July 26, 2001.

One other point. If you change the ISO on the camera (say you're pushing 400 to 1200) rather that just being aware you are underexposing the film, you stand the chance of unnecessarily underexposing some of your shots. There may be just enough light to properly expose a frame, perhaps with the help of a tripod, but because you have changed the ISO on your are misled.

-- r (ricardospanks1@yahoo.com), July 27, 2001.

I usually use pull when there is a diffrent between Highlights & Shadows [zoon system] & push becasue of the efect of aviable light [people like it in a wedding photos]

-- AviB (bloombi@hotmail.com), August 21, 2001.

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