Hi Deb, I think they're giving you BS, unless there was something you were trying to photograph that needed to be exposed a certain way with ISO 200 film. For example, if you take a picture of your friend in the daylight with ISO 200 film and have the camera set for ISO 200, you'll get the correct exposure. If the film is then pushed to ISO 800, the film will be badly overexposed -- in effect, you used a setting that was correct for 200 film on 800 film. But for celestial objects, the camera setting doesn't matter. You're probably not going to overexpose the comet. On the other hand, you will get more grain, which is objectionable, with 800 film. So you have to weigh grain versus exposure. If you're going to push it to 800, why not start out with 400 film? Just some thoughts. Best wishes, Joe