When film was king, infrared photography was a specialized and tricky endeavor. Photographers who wanted to experiment with it were faced with challenges like keeping the film cool at all times and learning how to focus properly to get a sharp image. IR leaks in cameras were discovered by a trial-and-error process that frequently resulted in frustration, as whole rolls of film would be lost before one realized that there was a leak at all. When it came time to process, only a few labs had the expertise and facilities to handle IR film, and as if a roll wasn’t expensive enough, the processing costs were often at least two or three times the usual cost for a custom-processed roll of black-and-white.
By comparison, shooting digital infrared is easier and cheaper in every way. Once you have a camera converted, the shooting costs are practically negligible. You can see your results immediately on the LCD monitor and make adjustments before you miss the shot. The tedious practices of safely handling film are gone completely and, thanks to the D-SLR construction, IR leaks are practically unheard of.
Infrared camera conversion is done by removing the sandwiched anti-aliasing filter and infrared cutoff filter from the D-SLR and placing a new infrared high-frequency glass optic in its place. The infrared cutoff filter prevents infrared light from reaching the image sensor, so removal of this filter is the primary change within the body to allow the capturing of an infrared photograph.
Several companies convert cameras for dedicated IR use. The process differs slightly, depending on the company and what kind of IR conversion you want. The anti-aliasing filter combined with the infrared cutoff filter is what keeps your camera from absorbing the infrared spectrum—as a way of blocking or blurring it out.
One such company, LDP, has three options for infrared conversions. High Resolution keeps the infrared cutoff filter, but replaces the anti-aliasing filter. This specific conversion lets you take maximum resolution and color-separation photos without any filters. In IR-only conversions, autofocus and auto exposure work with any lens, giving you an IR-only picture. IR+Visible allows the image sensor to see infrared, ultraviolet and the visible spectrums of light.
Life Pixel offers a number of choices. Standard IR is a straight black-and-white infrared conversion. Deep BW IR is a black-and-white infrared conversion, but provides for broader better contrast and tonal ranges. Enhanced Color IR lets more color pass through the new filter. Enhanced Color IR is especially good for color infrared work, giving you saturation and a broad color range. The benefit to this sort of conversion is that it allows the camera to record the visible spectrum and infrared light at the same time. With the Enhanced Color IR conversion, however, you have to use a filter and you can’t see through the lens.
The Making Of An IR D-SLR
Camera manufacturers avoid aliasing in an image by using an anti-aliasing filter to blur it out, thus preventing moiré patterns. An anti-aliasing filter is also known as a low-pass filter, which passes low-frequency information and blocks out high-frequency information. The Nyquist Theorem states that aliasing can be avoided if the frequency is greater than the bandwidth, or the maximum frequency of the signal being sampled.
“So what does all of this mean to photographers? In most cases, a camera without an anti-aliasing filter will produce a sharper picture,” says Dan Llewellyn, president of LDP. “A landscape photographer will get about 30 percent more detail and better color separation when using a camera without an anti-aliasing filter. On a stock camera with an anti-aliasing filter, a black pixel next to a white pixel will result in two gray pixels. On a modified camera, you’ll get a black pixel and a white pixel. On a stock camera, a blue pixel next to a red pixel will result in blurred purple pixels instead of blues and reds. A modified camera will give you a greater range of colors and details. This can be verified by the increase in file size on our modified cameras.”
Customizing Your Conversion
As vital parts are being removed (the anti-aliasing and infrared cutoff filters), the camera needs to be recalibrated to work with lenses again.
Life Pixel calibrates Canon and Nikon bodies to specific lenses; for an additional fee, you can have a different lens of your choice calibrated. For Nikon, they calibrate their conversions for the Nikkor AF-S DX 18-70mm lens; for Canon, it’s the EF 50mm ƒ/1.8.
“Different cameras can be adjusted with different methods,” says Llewellyn. “Basically, since the infrared cutoff filter/anti-aliasing filter will have a different refractive index than the replacement made to the same thickness, you have to compensate somehow. You can change the physical position of the sensor, change the position in our refractive index of the filter replacement, adjust the AF sensor or make an electrical programming correction if the camera is a type that uses a software error lockup table rather than actually getting everything optically aligned. Basically, you need to do something. Our conversions will focus sharp at ƒ/1.2 at one foot for most lenses.”