This thread has been started to avoid going off topic in the UK meeting thread.

Rob (Stanwax) came up with the brilliant idea (some time ago) of using camera lens filters in order to provide a reasonably priced way of protecting the laser aperture on your projector.

I have purchased a UV filter for my projector and i believe Rob has a Skylight filter for his. Trying to find transmission curves from the manufacturers on these filters is no easy task (they do not include any information with the products), also, there seems to be little information on the internet.

However, after some searching I have found a usenet thread here...

If you scroll down to the bottom of the thread there is this posting...

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A link to a transmission chart that shows how different the
characteristics of UV and Skylight (1A) filters are:

A UV filter attenuates actual UV more strongly, and so will be a better bet
where excess UV is a problem - near the sea, at high altitude, at very low
latitudes. (This issues arises because film can see UV light, and renders
it blue, that the human eye can't see: so an excess of UV that is invisible
to us will make photographs look too blue, and also add haze to distant
views.) A UV filter should attenuate visible light very little, but it will
reduce the extreme purple end.

The Skylight doesn't attenuate UV as much or as sharply, but it does take
out a little more of the visible light, notably in the blue-green range.
This means it makes scenes look slightly warmer. It is designed to correct
for the excess blueness of scenes shot in shade on cloudless days, or
outside generally when cloud obscurs the sun - ie. when the light is coming
mostly from the blue sky. Definitely helps (on slide film) if taking
portraits in shade, but the effect is not _that_ marked otherwise.

I use UV filters more often than Skylights, but I do sometimes use a
Skylight in shade. For warming per se I'm more likely to use an 81 series
or a KR filter.
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Hope this is of assistance for anyone thinking of going down this route. If anyone has further information regarding these filters please share it.