I recently participated in a workshop for infrared photography at the Victorian Rose Garden in Roger Williams Park in Providence. Infrared photography is very interesting, as it reveals to us things we cannot see with our natural eyes. The name “infrared” reflects that the wavelengths are near the red end of the visible spectrum. In other words, we cannot see them, although they are there. The infrared spectrum is actually very broad, involving more frequencies than the visible spectrum. Digital camera sensors are sensitive to a little bit of this spectrum. In order to keep those frequencies from distorting the color of images, camera manufacturers put a blocking, or cut filter in front of the sensor, which allows only visible frequencies to pass.
To get around this limitation, some photographers choose to remove this cut filter, thereby allowing the camera to receive visible light as well as a little bit of the infrared (and even ultraviolet) frequencies. With the impediment of the cut filter removed, a filter on the front of the lens can be used to isolate particular frequencies of infrared light. Typically, these filters may allow 590nm, 720nm, or 830nm to pass. The larger the number (or wavelength, in nanometers), the farther the frequency is from visible light. The 830nm filter, for instance, does not allow any color to pass, yielding an entirely black and white image on the sensor. The 720nm filter allows some color to pass, and the 590nm allows quite a lot of color.
With a few steps of processing in Photoshop and Lightroom, photographers can enhance these images. One effect is that organic materials, such as foliage, looks white, whereas the sky and water is dark. Some weird color effects can be produced with several tweaks in processing software. This image, taken from inside the gazebo, for example, even recovers green in the foliage.
Personally, I prefer processing infrared images as black and white. Even though a 720nm, or even a 590nm filter, admit color to the sensor, the presence of color frequencies allows for refining the contrast in black and white. For example, I used a 720nm filter for the workshop. That allowed me greater flexibility in processing this image of the bandstand, elsewhere in the park.
Here are some other images from the workshop.
Very interesting, thank you. I have seen a study that shows that (at least some) birds have UV markings known only to other birds. As for human viewing, I prefer the black-and-white images also.
Thanks, Joel. I hope to explore more with IR soon.