Edward Ingold , Dec 05, 2009; 08:41 a.m.
The Cokin filter holders I've seen are pretty leaky. Unless you completely exclude visible light, you won't get a good IR effect.
What is this discussion about "white balance?" IR images don't have a white balance - they are monochromatic (or green). You don't get false color, as with IR Ektachrome, because that film is designed specifically for false color (with one IR sensitive layer).
The Nikon D100 seems to do pretty well with IR. High-pass filters got a lot better with succeeding models. My D2h has color problems with IR under incandescent light, but has limited sensitivity with an "expensive" IR filter. I do get the IR effect, however.
The real solution is to recycle an obsolete DSLR, and have the sensor fitted with a low pass filter. That's the only way you can actually use the camera without live view.