lens

[pacificnw]

Hi All,
I have a lens that has 317mm focal length and is 133mm diameter, is that enough info to tell me if it wiil work with my 15" lcd? And what fresnels would I use?
Any help is great, thanks.

 

[superdaveumo]

Almost. You need to know the viewing circle (related to field of view) of the lens. To find this, make a series of concentric circles on a white piece of paper starting in the center of the paper. Place the paper with a light behind it approx where you'd like to place your projector. Have the paper facing the wall or screen. Take your projection lens and place it in front of the paper (between the wall and paper). Focus the projected image (seen on the wall) until it is crisp. Count the number of circles on the wall (starting from the center most circle) you see in focus. Go back to the paper and find out the diameter of the largest circle you saw in focus. This is your largest diagonal screen size you can use and still be completely in focus.

It might help to put some lettering on the paper too to make it easier to focus. Good luck!