This is one of my IR Cameras.
I took a old Canon XT (8mp) and removed the factory UV/IR filter and replaced it with a piece of Edmund Optical Corp. clear optical glass. I had our glass shop (at work) cut it down to size. Following one of the many instructions on the web I swapped filters. The only tricky part was changing the shimming because of the different refractive index of the materials and thickness. Otherwise the focus you saw in the viewfinder and the image plane would be different.
My original intent was to make a camera for astrophotography to capture the hydrogen alpha wave length from emission nebula. It worked great. By using a 720nm or 850nm filter this camera can be used for IR photography. And, it's much more sensitive than IR film, not to mention grainless.
Newer DSLR's with live view are the way to go. I can't see a thing through the camera once the IR filter is attached and I have to rely on the lenses red IR mark and aim using a Leica finder. Digital allows me to experiment in the field until I find the perfect exposure. Film requires bracketing. This is shown using a Nikon 20mm f2.8 AF with a Nikon to Canon adapter (because I own all Nikon glass).