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Yes, it is the IR cut filter, and due to its thickness, it may be the 1/4 wave polarization filter also. And/or an optical low pass filter to reduce aliasing.
Wayne is right-IR cut is needed for CCDs, and manufacurers would frequently play games with how much red to cut. I recall once Sony sending me 3 filter designs, each with a different amount of penertration into the red region. They were chasing another Japanese company who had the highest marker share at the time.
IR drives CCD camera designers nuts, so it must be reduced before it hits the imager.
Let me know if you find a source, as I have seen Sony cameras with the problem that you describe.
One bit of caution-the thickness of the filter package must be exactly the same as the original, or you might run out of back focus adjustment range on the lens.
Regards,
JB
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