I have 2 lens. There fl is around 210mm and 170mm give or take a couple mm is there any way they could be used in my projector, a pre-condenser or something else. Thanks

It depends on how heat tolerant they are. A pre-condenser needs to be very close to the lamp to do any good, which is (as you may well guess) a very HOT location. Many glass lenses will crack or outright break under these conditions.

Well the lens were from a telescope or something like it. So I guess they wont be very heat resistant. What about really good cooling to keep the lens cool.

I don't think that adequate cooling is possible that close to the lamp. Not without adversely affecting the lamp, for sure.

Some people have had thir precondenser lenses crack and it works anyway. Just watch your fingers when it's time to replace that lamp. (Of course this will be years down the road, and you'll have forgotten this warning by then.

whats the diameter of them?

This is a guess since I am out of the house the 210mm fl lens is prob 4 cm in diameter, and the smaller fl is prob. around 3 cm.

4cm diameter is too small to be a useful precondenser. It may be worth a try, but I think that 6cm diameter is pretty much a minimum to get useful coverage of the lamp to the LCD area.

This would be okay for a smaller panel, but not for a 15" or larger.

Well like I said I am not sure of the diameter. I will measure the lens when I get back.

Ok so the big one is really like 6.5 cm so would that wrk?