Re: Will IR Illuminator work with any CCD Camera?

[davem@xxxxxxxxx (Dave Martindale)]

"Brian" <b.blandford@xxxxxxxxxx> writes:
>
>Charles Sullivan wrote:
>...
>>
>> As I understand it, the reason for including an IR filter is that the
>> focal planes for IR and visible light are different enough that there's
>> a noticeable blur in the image if both sources are present, as in
>> sunlight.
>
>There is a more serious problem, and that is the fact that silicon is
>transmissive in the near infrared (it is opaque in the visible). That
>means that the NIR radiation falling on one pixel will travel through
>the detector material and light up adjacent pixels, degrading the MTF.
>There is nothing a lens can do to fix that, you just have to filter it
>out.

On top of all that, if the Bayer filter matrix uses organic dye filters
(not multilayer interference filters), they are probably transparent to
IR.  That means that IR light passes through red, green, *and* blue
filters, and looks like white light to the sensor.  This desaturates all
of the colours in the image.  Blocking IR is necessary to avoid this.

If the camera did use interference filters (I don't know if any Bayer
matrix filters are actually done this way), the IR would likely pass
through only the red filter, and look like excess red light.  This still
messes up colour reproduction, because objects look redder to the camera
than they do to the eye under IR-rich illumination.

	Dave