Simple infrared photography is accomplished by putting an infrared filter on the lens of a camera. The problem is that most digital cameras filter out most infrared light requiring long exposures. The Fujifilm X-E2 and the Nikon D100 have semi-weak filters allowing shorter exposure times with infrared light. Older/earlier Canon cameras also have weak filters. If going this route then use preset white balance and measure it on the foliage of a tree or on grass.
The better solution and the one used here is to have all filters removed from the digital camera's sensor making it a full spectrum camera. Then use external, screw-on filters to filter out the undesirable, visible-spectrum light. Notice that the DSLR camera's live preview must be used which means it may be hard to compose shots in bright light. This is why a camera with an EVF is desirable for infrared work.
Black and White Infrared
B&W infrared filters let no visible light in. They are opaque.
The stronger the infrared filter then the lighter foliage will be and the more contrast the resulting image will have. See the below images for a comparison between 950nm, 850nm and 760nm filters — all of which are for B&W imagery. Notice that the contrast goes up as the filter becomes stronger and the shadows lessen. The purer the infrared light then the more dream-like the image.
Now, the contrast and brightness have been turned up slightly in Photoshop.
Clearly, the 950nm filter produces the cleanest images that are more surreal.
False Color Infrared
False color infrared is achieved through the use of a 720nm to 680nm filter. A little light can be seen through a 720nm filter with more light visible as the filter includes more visible light. The white balance has been set on the foliage.
Using the Image ⇒ Adjustments ⇒ Channel Mixer in Photoshop: for the Red Output Channel set RED=0% and BLUE=100%; for the Blue Output Channel set RED=100% and BLUE=0%.
High Dynamic Range and Infrared
Focusing Lenses for Infrared
Most lenses need to be focused slightly shorter than what they are when focused using visible light. So to focus to infinity, the lens must be focused slightly less than infinity. Older, manual-focus lenses have an infrared focus marker to aid in this and these lenses can be had for very little on the used market.
In the center of this image is an infrared "hot spot" from the lens. Some lenses have hot spots and some do not. Typically, the smaller the aperture, the greater chance that a hot spot will show up but some lenses show no hot spots regardless. The reason hot spots tend to show up in smaller apertures is because the infrared light is reflecting off the diaphragm blades.
Removing a camera's infrared blocking filter can make it into an infrared camera and the exposure times will drop significantly meaning movement will not blur the image. Visit the external links for access to services about removing the IR filter from your camera.