Slynky - Wolf explained it pretty well. When you take your film to be developed, tell them to push it 1 (since you went 1 stop from 200 to 400). And yes, you can pull film too. Many people I know pull Provia 100 to EI 64. or rate Velvia 50 at EI 32. You just need to make sure that your developer knows what you did and be prepared for a little more cost to develop the film (some places don't charge, others will charge a single fee for "x" amount of rolls developed in the same rack). Many people pull film to increase saturation. By pulling it, you are basically slightly overexposing the film and then developing for less than normal time to compensate. In both pulling and pushing, you are effecting the contrast of the negative. You can generally push/pull print film a lot more than slide (print has a much greater latitude than slide). But you need to watch how far you push or pull it. Talk to your lab as they may not be able to develop it (when I shot Ilfored Delta 3200 at EI 12500 I had to take it to a different lab for hand processing). As for how far it can be pushed/pulled, every film has its own characteristics. It also depends on how it is developed (time, temp, developer, etc.). I've seen some b&w pushed only a stop and developed to have grain the size of freaking golf-balls and I've seen some pushed 4 stops and having small, fine grain. It just depends. Best place to see what a film can do is to go to the manufacturers website and download the datasheet on the film. -=>Donald