Light is a strange thing. What we usually call light is only a small part of the entire electro-magnetic spectrum. Like our ears, the eyes are only sensitive to certain frequencies of light, but there are ways to see beyond.

As a physics student, I've seen the figure above in almost all my books. Feel free to think of light as you think of sound. The different notes of sound is a direct consequence of its frequency. A high voice has a higher frequency than a deep bass voice. In the figure above you can see the low frequency radio waves, with wave lengths of up to many meters. Moving to the left, the frequency increases. We see that the visible light only is a small section of the spectrum. To the far left is gamma rays, which is what I'm working with on my master thesis.

Notice to the right of visible light, there is infrared (IR) radiation. Our eyes are not sensitive to infrared light, but the sensors in a digital camera is. This can cause some problems in the camera, and because of this there is a piece of glass, often called a hot mirror, that blocks the IR from getting to the sensor. Depending on the camera, almost everything is blocked, or only some of it gets blocked.

It's very easy to check this: just take a controller (tv, cable, etc.) and look at it through your camera while pressing a button on the controller. Most controllers work by infrared signals, and while your eyes can't see it, a camera will. In my experience, good and expensive cameras will have good hot mirrors, blocking almost all the IR out. Less expensive compact cameras can let through a lot, and this allows us to use them for IR photography.

The infrared filter

To sum up: objects reflect light, and most of our light comes from the sun. The sun shines a great deal of infrared light, so objects will reflect IR light to some extent. Most of this light is blocked inside your camera, and the amount of visible light will drown it anyway. The IR filter is placed in front of your camera, and it blocks everything with a frequency above infrared light. In my case the filter is a 720nm Green.L (see the first figure to confirm that this will stop visible light).

The filter is totally opaque (you can not see through it), but it will let IR light through, so don't look at the sun through it!Since it is quite dark, expect the shutter time to become long. On a bright day it's about 0.5 seconds in my case, so it makes hand-held photography difficult, but as we shall see: not impossible. All photos in this article is hand-held.

The photos

So what is special about IR photography? Why go through all this stuff about wave lengths and frequencies? It's different, it's something else. It makes you look twice, at least it does for me. Ever since I saw a good IR photography, I've wanted to take them myself. The most striking difference is the color of course. We can't really talk about color in IR photographs, but let's do it anyway. Things that reflect IR well becomes bright, and since IR photographs typically are in black and white, they come out white. This is particularly so for green leaves, grass and foliage.

Let's look at the photos. Please keep in mind that these are the first attempts on IR photography on my behalf. Perhaps later I can dazzle you with something impressive, but these will do for now. Below are three photos, when you move your pointer over them they change to the IR photo. I did this hand-held, so there is a small differences between the two. I had to mount the filter between the photos, so the composition is not exactly the same.

When I got the filter there was a certain place I knew I had to go straight away. It was to the large tree next to Festningen in Trondheim. When summer finally comes I will do this photo again, and it will be stunning (I hope).

There is no doubt that this photo is the best of the three, and I think it shows off what IR photography is all about. Note that the cold sky is almost dark, and how nice the clouds looks against it. The thin foliage on the tree and the grass is nearly white.

There is a great deal of information about IR photography on the Internet, and it goes into much greater detail than what I'm doing here Introduction to Full-Spectrum and Infrared photography Infrared (IR) basics for digital photographers Wikipedia - IR Photography. If you want to see some professional IR photographs, please visit this link.