First, on-lens infrared filters are so dark you cannot see the subject throught the camera's viewfinder while the filter is attached to the lens. Normal Infrared film shooting required framing your shot before attaching the IR filter on the lens. Second, Infrared light causes focus issues unless the camera has been calibrated for correct focus. (Infrared Light transmission is at a different wavelength than visible light, creating a variance in the focal plane, resulting in focus differences. Earlier lenses have IR focus markings to help with IR focus adjustments.) Third, this caused longer shutter/exposure times due to less light reaching the film and limited ISO availability, limiting the ability to shoot moving subjects under darker situations with out them being blurred. This also required the use of a tripod for most scenic pictures otherwise causing blurry images.