actually, to get the Vader more red, you need a longer exposure time, and often, a lower ISO will get you a longer exposure time. Ya see, the ISO is the film speed that is simulated and a 100 speed film has more silver nitrate emulsion on it than a 400 or 800 spead film, so, it takes longer to develope and records more movement. I've noticed that if I do a really long exposure on my vader, I get a red blade, but a shorter exposure gets an orange blade, so, when I take picture of my lightsabers, I tend to use a 100 speed ISO.
Let me put it this way: if you use the 100 speed, you get more of the picture than if you use the 800 speed, since it will absorb more light than the 800.
I'm a photo-dork ::)