I have a basic question about grain, and what causes it other than ISO. I've done extensive google searching on photo.net and the internet in general to no avail. I'm aware that high ISO films will have higher grain, but with film and developing conditions identical, are there any other factors that contribute to grain? In my last roll of film of Ilford HP5+, I took a picture outdoors in plenty of sunlight (1/125, f16), and another indoors with limited light (1/2 sec, f8). Sorry, I don't have access to a scanner to scan them in, but both were exposed properly, in the sense that fstop and shutter speed gave identical metering readouts. However, the outdoors photo had significantly less grain in the final 8x10 print than the indoors one. Since this was on the same roll, the ISO and developing conditions were obviously the same, but I don't understand why the indoors photo would have much more grain. I've read that low light conditions can contribute to grain. Is this a factor independent of ISO? In the indoors picture I needed a 1/2 second exposure to take the picture -- would the longer exposure time required to expose the negative be the cause of the grain? This would seem unlikely because I've read that barring lens imperfections and reciprocity failure, the same photo with different fstop/shutter speed combinations won't affect grain/quality. So I'm pretty confused why I'm observing different amounts of grain. I would appreciate any help or insights you could give. Thanks!