Making cameras see things that our eyes cannot is something that’s always really fascinated me about photography. Whether it’s super extreme macro, infrared & ultraviolet or, as is the case here, heat and shockwaves.
In this video, Kelly Hoffer at Theory of Curiosity talks us through Background-Oriented Schlieren (BOS). It’s a technique that lets you see heat and other atmospheric distortions in photographs. Here, Kelly shows it off using just a regular camera and Photoshop.
The principle is quite simple. Shoot two sequential images of something that has some kind of heat signature. In this case, a candle. Then bring them into Photoshop as separate layers, and set the top one to Difference blending mode.
What you see as a result is where the light has bent as a consequence of having to pass through the candle’s heat wave before reaching the camera. So, the background behind the candle becomes slightly distorted. The Difference blending mode then lets you see just these distortions.
It also works for video, too. Although, depending on your camera, the results might not be as great as you’d expect. With a 10-Bit codec, like that found in the Panasonic GH5 or Fuji X-T3, you’ll probably be ok. With 12-Bit RAW like the Blackmagic Pocket Cinema Camera 4K, it should be as reliable as shooting stills. But if your camera shoots 8-Bit video, especially if it’s at a fairly low bitrate, then you may have to deal with compression artifacts that can cause a lot of unwanted noise in the final result.
Kelly shows off several samples in the video, including some highlighting the video compression issue I mentioned, and it’s a pretty cool and interesting looking technique.
Sure, it’s not your traditional photography, but I bet it could make for some wonderful and unusual results. Another experiment going on my list for the future.