The first issue with shooting IR is that the sensor in the digital camera is NOT very sensitive to IR light, because it has an IR blocking filter...
'Infrared' is the part of the electromagnetic spectrum with wavelengths longer than the visible light. Infrared radiation is usually discusses as three parts:
- Near Infrared (700-1200 nm),
- Mid Infrared (1200-3000 nm), and
- Thermal Infrared (3000nm-1mm).
IR photography uses Near Infrared. But digital camera CCD and CMOS sensors are sensitive to visible light with wavelengths between ~390 and ~700 nm.
If you can see the beam of infrared light, your camera’s IR filter doesn’t fully block IR light and some makes it through to the sensor. This means your stock digital camera is capable of capturing near infrared light, unmodified but the exposures may be quite long.
The second issue is that the IR filter merely PASSES IR light while suppressing much of the visible spectrum. Because infrared film is sensitive to visible light as well as infrared light a special infrared filter needed to be attached to the front of the lens to block all visible light and only pass infrared light.
The third issue is that Infrared light, being located to the right of visible red light, has a longer wavelength and focuses at a slightly different point. Because of this most lenses have a red infrared focus dot offset from the regular focus mark.
With Digital, it is still possible to shoot digital infrared photography with an unmodified digital camera but the exposures become quite long and in most cases require a tripod, not to mention the need to place an infrared filter in front of the lens to block visible light. After a digital infrared photography conversion it is possible to photograph infrared images hand held at low ISO speeds and without the need for infrared filters