I have just got a lens that looks like it came from an old camcorder (i upload 2pics)
I was wondering if I could use this in a diy projector instead of the lens that you have to order?
and if i can is there a way to tell the fl to it and the end is adjustable (It can extened)

If it's from a camcorder, you'd probably need to have an LCD that is around 1" diagonal in order to use it, about the size of the camera's CCD.

For DIY purposes, that's not a usable lens.

well im not 100% sure it cam from a camcorder, do u want me to take some mesurements to be sure of how big the lcd could be?

there's another pic of it striped a bit

It looks way too small. If you really want to get a really rough idea of what the max size the LCD can be though...

The focal length would be one side of a right triangle, then you can measure the angle of the maximum field of view (based on how long the tube is and the lenses diameter). Then you have a triangle with 3 known values. Calculate the length of the triangle's base and you have the largest size a square LCD monitor you can have.

Thats assuming your fresnel lenses are focusing to the very center of the lens, which in reality I don't think it does (something about focusing to infinity).

I think thats how it works anyway.

I dont understand that at all (can u explain it with a pic?) ....there is 2 lenses one in the front and the back
Is that how its suppose to be?

Click to view attachment

You can estimate inner angle with a protractor or by figuring out the similar triangle int he middle.

@Owen: Actually, that's not the way that it works. The lenses alter the light path through the triplet signifigantly, and you cannot assume a straight path through the triplet.

First off, you DO need to find the FL of the triplet. Anything less than 200mm isn't going to be usable, no matter what the FOV is. 200mm is suitable for LCDs of 8" or less anyway.

You can ROUGHLY determine a lens' FOV with a straightedge and a ceiling with overhead flourescent fixtures. Having a ceiling 2 stories up would be needed for a meaningful measurement. Using the lens so that the external side points at the flourescent fixtures, focus an image of the fixtures on a surface below the lens. As the fixture gets closer to the lens, that focal point will be further away from the lens, so we really want this to be as far as possible for starters.

Now, you have an image showing 4 or more flourescent fixtures on your table. Use the ruler to see if the edges are straight. If not, you've got speherical distortion at that image size, meaning that you're crowding the lens' FOV. If you can't get a clear focus on the whole thing, that also indicates that you're out of the lens' proper FOV as well, also if you get a red or blue edge around the image of the lights.

Different distances will give you a different "lcd size" so you can test.

The area that the flourescent fixtures cover on the ceiling would be your projected screen size if the image of the fixtures were your LCD.

alright then.....i think ill just go with the lens from lumens lab store
one more question.....does the light base come with anything or do u need to buy it separetly?

Light base?

For the MH lighting, you need 3 things. The lamp, the socket, and a ballast.

The socket (Or base) will have wire leads to connect to the ballast, and the ballast will have leads to the lamp base long enough for a reasonable mount location, but it wouldn't hurt to have some 14 gauge wire around to take care of misc things.

I understand that......i was wondering if the lamp socket came with anything or you have to buy it separetly?

btw thanks for all your help

Well, if you get the light "kit" it'll come with the mogul, otherwise, buy separately. It does not come with the ballast.

ya i was wondering because when i add it to the cart it does not add the socket