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Infrared Photography
2008-08-22

Introduction Infra-red is what comes beyond the red end of the rainbow. Our eyes can't see it. IR photography is fun because green trees and plants reflect a lot of IR so they look very bright in IR. Likewise blue sky has almost no IR, so the sky looks black and clouds really stand out in IR. Haze and fog scatter blue light and have little effect in IR, so IR images cut through much haze and fog. There are many different kinds of IR. "Near" IR is IR close to red in the spectrum. This is what we photograph. Near IR is not heat. Heat is longer IR much further away from red and not photographable with ordinary equipment and film. Scientists describe colors with wavelengths. Blue is from 400 - 500 nm (nanometers), green is from 500 - 600 nm and red is from 600-700 nm. IR starts at 700 nm and for photography extends to about 1,000 nm. 1,000 nm is called a micron. Longer wavelength IR used in systems. Filters Filters are the key to IR photography. Unfortunately they are both expensive and a pain to use since they often are totally black! IR systems are also sensitive to ordinary light so filters are used to eliminate the visible light to get the IR effect. This can be a pain because "eliminate visible light" is a fancy way of saying these filters are black! If you need to focus or compose through the lens use a tripod and attach the opaque filter just before the exposure. Cameras with separate viewfinders are perfect for IR since you don't put the black filter over your finder. Some IR filters allow some dim red light to come through so you can compose with the filter attached. An ordinary red #25 or R60 (same thing) filter works fine for B/W IR film. You can get one here or just about anywhere. It lets you see what you're doing and eliminates any blue or green light to which B/W IR film might be sensitive. This gets you nowhere for digital cameras and is just an effect for color IR. Other red filters, like the deeper #29, do the same thing. The 89B (B+W 092) filter (I'd get it here) is a very dark red, allowing light redder than 650 nm and IR to pass. This is a handy filter since you can compose through the lens and can try to use a filter factor of about 20 - 40 with regular B/W film. This is probably the most practical filter for most people. Don't ever dare a friend to look at the sun through one of the black filters, since of course all the IR comes through and will blind your ex-friend into seeing black forever. It's very dangerous because your eye sees black and opens wide, letting in far more dangerous heat and IR than they would if you looked stright at the sun with no filter. Film infrared photography Infrared film of many types has been available for decades and photographers have been using it successfully but not without some trial and error in their photography. If you ask any photographer who shoots or has shot infrared film he or she will tell you that it is a hassle and much more difficult to master or even get good results with over regular film photography. Here are a few reasons for this: Since infrared film is very sensitive to infrared light as well as visible it has to be handled, loaded and processed in complete darkness. Photographers have gone so far as to use blackout tape on the film window and around the film door on their camera to prevent light leaks fogging the infrared film. This was done even if the same camera didn't exhibit any light leakage with regular film photography. Because infrared film is sensitive to visible light as well as infrared light a special infrared filter needed to be attached to the front of the lens to block all visible light and only pass infrared light. Since all visible light is blocked by this filter we can’t see through it as it is opaque black to our eyes. As you may have already realized this makes it impossible to compose and focus as you no longer are able to see through the viewfinder. To overcome this problem the filter needed to be removed, the photographer, using a tripod composes and focuses, attaches the opaque infrared filter and takes some bracketed photographs. This process would need to be repeated over and over and over. Infrared light, being located to the right of visible red light, has a longer wavelength and thus focuses at a slightly different point. Because of this most lenses have a red infrared focus dot offset from the regular focus mark so that the photographer after focusing on visible light can move the focus ring to align with the red infrared focus dot. Lastly, infrared film only has a suggested ISO rating because the amount of infrared light varies from scene to scene independent from visible light. This would require the photographer to take a series of bracketed exposures in hopes that one would be correct. As you can see the steps required for film infrared photography are quite lengthy and complex compared to regular visible light photography and many have given up after some failed attempts. Digital Infrared Photography With the advent of digital cameras it is now possible to photograph infrared light with your digital camera and greatly simplify the infrared photography process. The latest digital cameras are sensitive to infrared light, so much so that manufacturers place a hot mirror filter in front of the sensor to block infrared light to prevent infrared IR light from spoiling regular photographs. It is still possible to shoot digital infrared photography with an unmodified digital camera but the exposures become quite long and in most cases require a tripod, not to mention the need to place an infrared filter in front of the lens to block visible light. All this sure doesn't help the creative infrared photography process. With our digital infrared photography conversion it is now possible to photograph infrared images hand held at low ISO speeds and without the need for infrared filters. Since you no longer need to use an infrared filter in front of the lens it is much easier to change lenses, compose and focus. Covert surveillance with IR Use an IR light source and an IR sensitive observation system and you can observe others or animals in complete darkness, although they will look well lit to you. They won't see your IR light, but you can. In the old days people put #87 opaque gels over flashbulbs and used IR film to photograph people in dark places without their knowledge. I think Polaroid even made these filters for their flash cameras. Also one could put these gels over ordinary tungsten lamps. Today one simply uses IR LEDs and conventional CCDs. Of course if the bad guys also have IR systems this is also the best way to get yourself shot, since they will see your sneaky "invisible" illuminator and try to shoot you first. That's why image intensifiers that work without active illumination are preferred by snipers. Consumer IR systems are not sensitive to the longer IR wavelengths needed to see through walls or just see heat. This is not because of a secret government mandate; it's because glass is opaque to IR. The advanced long wavelength IR systems have to use special lenses made out of bizarre materials and are way too expensive for your basic neighborhood pervert. Likewise, they won't see through glass either.

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