Re: Will IR Illuminator work with any CCD Camera?

["J. Clarke" <Jclarke.usenet@xxxxxxx>]

On Sun, 31 Dec 2006 20:33:51 -0500, Charles Sullivan wrote:

> On Sun, 31 Dec 2006 13:11:41 -0500, Robert L Bass wrote:
>
>>> The one thing you will find is that many
>>> people who sell IR illuminators tend to
>>> flat-out lie about their performance
>>> (think used car salesmen).
>>
>> One source of confusion is that the camera manufacturers' literature often cites as range the maximum distance for "usable video."
>> The problem with this is usable video equates to "you can see something happening out there."  If your only purpose is to know that
>> something is happening but you don't care what it is or whjo is doing it, that would be ok.
>>
>>> My best performer is a forced air-cooled
>>> 500 watt flood with an opaque IR filter.
>>
>> Sunlight also works well.  :^)
>
> 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.
>
> I don't know to what extent this can be corrected by an achromatic
> lens as is used to correct for chromatic aberation on quality visible
> light cameras.

In the days when manual focus was the norm, any decent lens had markings
on it for IR focus as well as visible light.  There wasn't a huge
difference usually but it was there.  At the time the filter wasn't an
issue--most film didn't have much IR sensitivity--if you wanted IR you had
to use IR film.  With digital cameras it's not that simple because you
can't change the sensor--the manufacturer either has to put in the IR
filter and remove most of the IR capability from the camera or he has to
leave it off and field the complaints from the people who don't understand
that using an IR blocking filter on their lenses is the price they have to
pay for an IR-capable camera.

I don't know the best solution to that problem or even if there is one--a
built-in filter that can be easily field-removed would be one option but
that has its own issues.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)