Infrared is outside the visual spectrum with the Latin word ‘infra’ meaning ‘below’ and ‘infrared’ meaning ‘below red’. Below, in this case, means a longer wavelength, but the important concept is that it is outside our vision, much like other electromagnetic energy like radio waves, microwaves, heat etc. Digital camera sensors are highly sensitive to infrared radiation, even more sensitive to infrared than the visual spectrum, especially the blue component of vis light. This spectral sensitive bias to infrared is highly problematic for camera manufacturers and when shooting normal scenes and expecting ‘natural’ colour images from your digital camera. Interestingly, film is the complete opposite sensitivity to digital sensors. Film is more sensitive to ultraviolet and blue and requires dyes to be added to the black and white emulsion to make it more sensitive to green and red and, with specialised films like infrared. Digital cameras are manufactured to prevent exposure to infrared radiation and record average scenes with normal colour reproduction. The camera design solution is relatively simple, but a situation we must be aware of when conducting this type of photography. An infrared blocking filter is fitted to the sensor to avoid any infrared exposure by the sensor.

The advantage of this method is you can use the camera normally and frame the image through the optical viewfinder. The disadvantage, which is only a slight disadvantage, is that your infrared work is limited to a single infrared transmission filter. There are now several options available for this type of filter, some for black and white work and while some are designed for colour infrared. The difference between an infrared blocking filter and a transmission filter is evident in the description. Infrared blocking filters allow visible light to transmit through while rejecting infrared wavelengths. Meanwhile, the infrared transmission filter transmits infrared wavelengths and rejects visible light. Some infrared transmission filters allow certain visible light wavelengths to transmit, which alters their optical characteristics. To understand the optical filters' characteristics, consult the filter manufacturer's filter transmission curves. The second infrared conversion option is to remove the infrared blocking filter and add either no other filter or a plain coverslip. Removing the infrared blocking filter makes the sensor sensitive to both infrared and the visible spectrum, although sensors are more sensitive to infrared. The control of the results in this method is determined by adding an infrared transmission filter to the camera lens. The obvious advantage of this method is that now there is a range of infrared optical filters to fit the optical system of choice. While a single transmission filter attached to the sensor works fine for most photographers, with the possible exception for forensic or scientific photography, specifically those targeting a specific material (like gunshot residue or blood in forensics). A significant disadvantage of this second method is when an infrared transmission filter that rejects all visible wavelengths is attached to the camera lens. Because we don’t see infrared, the viewfinder is black, and the live view option at the back of the camera is the only way to frame and focus the image. While the second method offers more flexibility, the first is far simpler to operate the camera.

It is important to note that just fitting an infrared transmission filter to your lens without the camera body conversion does not work. While the transmission filter will transmit infrared through the lens, the infrared blocking filter on the sensor will prevent it from recording anyway. Sometimes, there are small leaks of particular wavelengths that may result in a slightly different image; however, the infrared blocking filter must be removed to perform this type of work.

The final word on infrared landscape photography is: why shoot in infrared, and why is it different? For creative practice reasons, it is simply a matter of aesthetics; infrared results are quite different from normal visible light photography. All photography operates on contrast due to certain objects absorbing or reflecting light or infrared radiation in this form of photography. Why do plant foliage and green grass have a snow-like appearance in infrared photography? Because the foliage and grass, which vary depending on species and the plant's health, reflect a lot of infrared light and, therefore, record in a light tone. On the other hand, the trunks of trees and the blue sky absorb infrared light and produce a dark tone in the image. Another variant to consider is the amount of infrared radiation that is present at the scene. Direct sunlight produces a significant level of infrared, while cloudy conditions produce less. A word of caution though…..use this method subtly rather than the effect overpowering the image design and meaning. Happy shooting!

Written by Glenn Porter - Updated 24 July 2024