Wednesday, March 4, 2015

Seeing Through Things

One of the most interesting things about infrared photography is that some things that appear opaque in visible light are transparent to infrared. Perhaps the most obvious example would be the classic R72 filter used for IR photography. This filter blocks all visible light while allowing infrared to pass.

R72 Filter with Visible Light Only

R72 Filter with Full Spectrum Camera

Neat, but predictable. Here is a pair of matte black sunglasses.

Visible Light

Full Spectrum Camera, R72 Filter
Notice how you can see the "O" shaped logo through the right temple in the infrared photo?

Here is another example. These appear even more transparent than the example above. The image was desaturated to remove the bluish cast seen in the above example.

Visible Light

Full Spectrum Camera, R72 Filter, Desaturated in Post

These are neat, but the most dramatic example I have found is sunglasses made from Acetate. These appear completely transparent when photographed with infrared light.

Visible Light

Full Spectrum Camera, R72 Filter, Shot in B/W

Notice how clearly you can see the metal frame? That is pretty well known way to verify that your Wayfarers are authentic, but if you have black frames it is normally difficult to see for obvious reasons. Not the case here.

Full Spectrum Camera, R72 Filter, Shot in B/W

What else?

The camera window on a WiiMote is a predictable one.

Visible Light

Full Spectrum Camera, R72 Filter, Shot in B/W

The camera can clearly be seen through the window, which is probably just a filter similar to the R72 filter I am using. This would also suggest that the "sensor bar" that the Wii uses is improperly named. Most likely it consists of a couple infrared LEDs that the camera in the WiiMote uses to sense movement. Unfortunately I don't have the rest of my Wii anymore to test that theory. Not that it really matters...

Here is an obvious example of the opposite situation. The hot mirror we removed from the camera during conversion to full spectrum is transparent to visible light and appears opaque when only infrared light is used.

Visible Light

Full Spectrum Camera, R72 Filter, Shot in B/W

A couple bonus pictures:

Light painting with a TV remote. More it faster to space the dots out, or slower to space the closer. Notice all the reflections caused by the filter?

Light painting with sparklers on an RC airplane, not at all IR related, but still neat.

A flame provides a strong IR source.

Visible Light, Dark Room. 1/10s, f/5.0, ISO 400 (EV100 = 6)

Full Spectrum Camera, R72 Filter, Dark Room. 1/30s, f/2.8, ISO 400 (EV100 = 6)
Although the photos were taken at the same EV, the infrared image is clearly brighter, evidence as to just how much infrared light is produced by the flame. The other photo looks a lot better though.