I thought i just better check a few things, I just purschased my first role of infrared film, and am planning to use it tommorow (assuming the weather is as marvellous as today) and was just wondering about a few things reguarding film speed. I've read up on the topic and think i know what i'm doing, but i want to use this as a test roll, so i basically want to try everything. This means i'll be using a R72 and 25A filter and try a variety of shots. Now my question comes because i was just wondering what peoples thoughts are on changing the film speed for successive shots on the same roll of film. It's been suggested to shoot the R72 filter at ISO 25 with the 25A filter at ISO400 this would mean if i wanted to try a few shots with each i must adjust the film speed. Can anyone advise me if this will be ok, i'm thinking from all perspectives here, including development. And if you do feel there may be a problem could you expain why and perhaps suggest another way if there is one... Thanks, Luke.