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Night Owl security bullet camera

Recently had to dismember a Night Owl security bullet camera as the mechanical IR cut filter was sticking, but that started with, what the heck is a Mechanical IR cut filter? Well… turns out that the sensor in CCD cameras is fairly sensitive to IR light as well as visual light. That ‘feature’ means great night vision, but not so great daytime photography, so most electronic cameras include an IR Cut filter in front of the CCD sensor so the sensor’s response curve looks more like a human eye response curve. Great for daytime photography, but it also kills any IR night vision. The solution of course is to remove the IR filter at light and replace it during the day. Hence the mechanical IR cut filter. The same signal that turns on the IR spotlight LED’s, causes the IR cut filter to be removed from in front of the CCD sensor. IR Spotlight turns off, then the IR cut filter is put back.

Here’s disassembly of a Night Owl bullet camera (a model CM-930-TU bullet security camera if you’re interested)

First, start with the bullet camera…

Night Owl CM-930-TU bullet camera

Note that the front and back halves of the body screw together with an o-ring keeping the seal between the. So simply hold in your hands and unscrew front from back

CM-930-TU front and back separated

Unplug the video/power cable comes through the back of the camera. unplug this cable from the camera circuit board. do NOT pull the wires, with a screwdriver pry out the connector from the socket. if you pull the connector out from the socket by pulling the wires, you’ll likely separate the wires from the connector. bad, bad. Once you have the video/power cable disconnected, you have the front half as a separate piece you can work with.

front half CM-930-TU camera

Now you can see the 2 screws holding the camera circuit board onto the front body. remove those two screws and gently remove the camera circuit board.


then disconnect the connector from the IR LED circuit board


with the IR LED circuit board uncovered, you can remove the 2 screws here and also remove the IR LED circuit board from the camera body

Now look at the camera body. note 3 screws holding the lens carrier on as well as a 4th screw in the very corner. The larger thin square plastic part underneath the lens body is the housing for the mechanical IR filter we’re after.


Remove the 3 lens carrier screws as well as the 4th screw in the corner. the lens easily lifts off and yields this:


To actually see the mechanical IR filter itself, gently slide the cover off of the filter holder. note two tabs on one edge and a single tab on the opposite end. slide about an eighth inch from the single tab toward the two tabs and then lift the cover off. that gets you this:


the mechanical IR cut filter is the flat rectangular carrier in the middle with one filter for IR and one for daylight. yeah there’s not just an IR cut filter there appears to be a another filter used at night. Notice the electric coil at the top. the action is a little like the head on a hard disk. energize the coil one way, the plastic lever arm moves shifting one filter over the CCD sensor. energize the coil the other way, the plastic lever arm moves the other direction shifting the other filter over the CCD.

At least in this camera, the round, clear filter is in place during the night and the square darker colored filter is in place during the daylight.

If you connect all the wires up with the camera still disassembled, you can see the mechanical IR cut filter in action.

Here’s a picture with my hand over the IR led flood light (simulating ‘darkness’) the night filter has shifted the round, clear filter into place. This allows the CCD sensor to ‘see’ IR light.


After removing my hand, (simulating ‘daylight’), the square, darker IR cut filter has shifted into place, thus blocking IR light from getting to the CCD sensor during the day.


check the IR cut filter module for smooth movement, remove any debris, anything that might cause the module to bind as it shifts back and forth. Then reassemble the camera by following the disassembly steps in reverse. all pretty straightforward.