Sean Ragan converted his old digital camera to sense infrared light better by changing out a filter in front of the CCD. He has some nice insights into the problems that could arise when doing this type of modification such as filter thickness and cutting one down to size.
10 thoughts on “IR-only digital camera”
His post mentions focusing issues arising from the thickness and refractive index of the replacement filter; there might also be issues arising from the fact that (in most lenses) IR light focuses at a different point than visible light. For this — among other — reason(s) it would be desirable to use a camera with the ability to manually focus and/or control aperture to increase depth of field.
Or as has been suggested, use a camera that will accept lenses intended for manual focus 35mm cameras. These lenses often had the focus point for IR marked with a red “R.”
SLR lens have a mark for how much to adjust the lens after focusing to compensate for IR (since after compensating it will look out of focus to your eye). I’m not sure what meh means by 35mm cameras. Point and shoot cameras never have the marking (35mm or digital), and SLR always have it (35mm or digital).
That being said, I used to shoot IR film in my 35mm SLR. And while I do love this hack, I can’t see a lot of people (including me) modifying a digital SLR body to do IR only.
It strikes me as funny that the autofocus mechanism isn’t working right. Most compact digital cameras autofocus through contrast detection. Or at least they do these days. It should be a closed loop negative feedback between the contrast detected on the sensor and the focus mechanism. Perhaps this old camera still used IR triangulation rangefinding. Or perhaps he moved the sensor completely out of the focusable range. Or perhaps he damaged the mechanism when taking it apart.
@Robert – if you read the posting, he didn’t move the sensor, he changed a filter *in front of* the sensor from one that absorbs IR to one that absorbs visible light.
As far as the auto focus mechanism, anything that it has which reacts to visible light, including contrast detection, will give a wrong result because IR bends at a slightly different angle than visible light when it passes through the medium of the lens.
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