Mid-quality USB cameras that have interchangeable lens filters?
Evan Juras wrote 01/20/2020 at 17:52 • 0 pointsI'm working on a project where I need to use an infrared (IR) camera that's filtered to only see wavelengths around 850nm. I'm interfacing with the camera using a Linux machine running Python OpenCV code, so it needs to be a camera that connects over USB.
From what I've researched so far, an IR camera can basically be made from a regular digital camera by using a special lens filter which only allows certain wavelengths of IR light to pass through it. (https://expertphotography.com/infrared-photography-basic-camera-gear/) There are also IR-specific cameras, but they tend to be very expensive (https://www.edmundoptics.com/p/EO-1312-NIR-USB-30-Camera/37395).
I'd like to create my own IR camera by getting a mid-quality USB camera and adding/changing a lens filter to an 850nm IR filter. Does anyone know of any mid-quality USB cameras ($30 - $150 range) that have interchangeable lenses/filters or would work well for an IR application?
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You can just put a filter in front of the (any) lens. That's how SLR camera lenses work, after all (though they have nice screw mounts that keep things parallel and cut down leakage and such.) IIRC, there was a Kodak Wratten type 87 filter that blocked most visible light, and an 87C that blocked even more of the visible. It looks like "name brand" filters are not-at-all "reasonably priced", but there are some cheaper versions like https://www.adorama.com/le87p3.html
It should be about like putting a piece of clear acetate plastic in front of your lens.
As others have mentioned, it'd be helpful to figure out whether your camera already has some filter designed to EXclude IR from entering the sensor (silicon sensors are normally much more sensitive to the near IR than film, so such filters are pretty common in color cameras.)
("Security cameras" with "Night vision" are more likely to be fully IR-sensitive.)
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It used to be logitech webcams that reliably had a removable IR filter in, not messed with one less than a decade old though. Also for a blocking all but IR filter, fully exposed and developed photo film, i.e. the "black" bits at the end of a roll of 35mm block visible and pass IR. (Raid granny's negatives) Not quiiiite sure of exact wavelengths, might be something like 650-950nm.
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Well regular camera usually have a filter that block IR. Nevertheless, 850nm is near IR so many webcam are able to see that wavelength. But to make your camera more sensitive, you'd better remove the blocking filter (if possible) before.
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