When you use an infrared filter on a film camera, you can’t focus because all visible light is blocked. However, due to the methods used to convert digital cameras to be infrared-enabled, it is often possible to use the camera’s autofocus and exposure systems with some caveats of course.
This is advantageous as trying to achieve infrared focus can be difficult, not only due to a lack of visible light but also because of the fact that waves of light focus at different points (infrared focus shift).
Most newer DSLR cameras come with a wonderful “Live View” feature that allows you to actually see live what the camera sensor is capturing and some even have the ability to focus directly from the imaging sensor while the life view is active.
This is incredibly useful in digital infrared photography as your camera gives you the ability to “see” infrared light before you even take a picture. This gives you a clear advantage especially with focus because now, even though there is a focus shift since the camera is seeing the IR light through the imaging sensor it can focus directly and accurately. There are still a few limitations though, we will discuss this later in this chapter.