Monday, November 26, 2007
DPP Solutions: Infrared Camera Conversion
Infrared photography has been transformed from a finicky medium full of frustration and technical difficulty into a field where anyone can try to expand their portfolio and creativity
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.”
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