Wednesday, July 8, 2009

The Myth of Digital Infrared

Every time I see an article on digital infrared photography I see the author saying he/she sent her/his camera out to be modified. What they seem to miss (or, if they know, fail to mention) is the fact that removing the IR filter from the sensor is an accommodation and not a requirement. What removing the filter accomplishes is reducing the time needed to take the shot. Today's image isn't the best infrared shot ever taken, but it was made with an unmodified camera. A Hoya R72 infrared filter was used with the camera on a tripod and an 8 second exposure at F22. Certainly not something you want to hand hold. The R72 IR filter passes light starting at about 700 nm (nanometers) and reaches peak transmission of light at approximately 720 nm. (Hence the "72" portion of the name.) If you had two of these suckers I'd bet you could make an excellent pair of welding goggles. You can't see "anything". I mean hold it up to the light and nothing, nada, blank, normal indoor lighting doesn't have a chance against this beast. To find out more about infrared with "normal" cameras, click the "read more".
The part of the equation the authors of the articles miss is that removing the IR filter from your camera reduces the shutter speed needed to take the shot. I haven't had the opportunity to use a modified camera, but I'm thinking, with the filter gone, you may be able to get to the point where you can hand hold a shot. If that's what people are writing about I'll go along with that. I've already conceded that I can't hand hold an eight second exposure. If removing the filter gets you down into the 1/30 of a second range, I can do that. Most infrared images aren't long telephoto shots. They're "normal" to wide angle shots. I'd give up a couple of F-stops and shoot all day at 1/30th and F 8. The Depth of Field (DoF) would be sufficient for most shots and the wide angle shutter speed is doable.
So, what am I missing? With an unmodified camera I'm giving up the possibility of taking hand held shots. Okay, if I'm shooting "serious stuff" I'm typically on a tripod anyway. I'm losing a couple of stops of DoF. Okay, if I have the tripod set to a "standing height", with a wide angle view, I probably have all the DoF I need. (With the focus at infinity on an 18 mm setting on a lens the minimum acceptably sharp area is probably fifteen feet (??) to infinity and the downward angle from "standing height" is probably twelve feet (??) before it hits the ground. The "out of focusness" (aha, a new word for the lexicons. Somebody got to make them up.) is probably still not offensive. If you're lying on your belly at the beach trying to get the beach, the rocks, the sea, the horizon, and the heavens in sharp focus you probably want to take that downward angle into consideration, but, we're at "standing height".
There are things to keep in mind if you're using an unmodified camera to play with infrared photography, but nothing that's insurmountable. The one thing that might cause you to pause would be the price of those filters. The tag on the 67 mm R72 Hoya at B&H is close to $90.00. To go to a 72mm, plan on shelling out an additional $200.00. Close to $300.00 for a filter to play with is a wee bit steep in my book. The 67 with a stepdown ring for the lens (a 72 mm to 67 mm Cokin at B&H for less than $15.00) is more in line with my pocketbook. You'll just have to keep in mind that you will be getting some vignetting and shoot to the center of your image. If you're going to make a living shooting IR, by all means, get the pricier filter. In fact, get the proper size for each of your lenses. If it's an experiment, borrow your buddy's setup.