okay i posted this elsewhere but then discovered this is the right place for it so you can delete it from the "intelligent design" section.

I'm looking for good long throw lenses for my 15" lcd projector project and i'm wondering what exactly should I be looking for? I found a couple lenses the say:

LCD PROJECTOR ZOOM LENS 145-265MM 1:4.5 &
ZOOM LENS 105-168mm 1:3.6 - 4.6

what do these numbers mean and would they work for a 15" projector?
ok i'm reguessing myself now on what those number mean...perhaps the mm's are the diameter measurements at the front and at the back?..hmm...
thanks!

The mm numbers are focal lengths, and the ratio numbers are the minimum f-number of the lens, which is a measure of the aperture - i.e., how much light will the lens let through.

I think for a long-throw lens, you'll want a longer focal length lens - LL pro is 500mm, and I don't know just how long you need, but you can play with DAZZLA's nifty focal length calculator program and have it compute the focal length lens you'll need, given your room dimensions, screen size, and desired projection size.

man..this is quite confusing. So I have to worry about the physical diameter of the lens, the f-value, and the focal length correct?

If I were made of money I would just buy the pro lens here but the lens alone would be more than the cost of the rest of my projector!

Here's what each factor affects:

Physical Diameter:
The larger the diameter, the easier it will be to get an image that doesn't darken at the edges. If you have your focusing mechanism set up to where to triplet/projection lens moves, you'll also be able to achieve a wider focus range.

F-value:
Smaller numbers are better. 1:2 is much better than 1:4.5. for every sqrt(2) decrease in f-number, you gain 2x light. Price will also increase, as low f-numbers mean really nice glass, sometimes exotic.

focal length:
Once again, play with DAZZZLA's focal calc tool to figure out what you need, then look for that.

As for the cost - I don't think you'll end up with a better lens than the LL pro for the money, especially for long-throw. It's not a bad deal, no matter how much the rest of your projector is, and it would be a worthwhile investment, in case you decide to build a better, more expensive setup. You might also check out DIYprojectorcompany, they have a long-throw lens that is a bit cheaper, I think.

i am in agreement that for what you are getting, the LL pro lens is a good price, I just didn't want to have to pay that much if I could get around it . I don't want to cut corners either though so I might just have to bite the bullet.

thanks.

i hope this isn't blasphemous..but could someone give a comparison of lumenlabs lens against the one @ diyprojectorcompany. The fact that they choose to show such terrible quality images in their "results" section leads me to believe their lens is of a much poorer quality..that or they are doing something else terribly wrong.