Would it not be easier to just use an overhead projector with a stripped lcd on top like the one in the picture?

Easier, yes.

Better, no.

If I have my history correct, a lot of the people on here started with the OHP project. The projectors we build on here are a result of many levels of improvement on that design.

Some of the improvements are in the lumens, focus, cooling, and simply the fact that those things are ugly as sin.

Thew bulbs used in those are expensive, not very bright, and often have color issues.

The light issues are further compounded because the light is not contained in a box, so the whole room gets lit up by the ohp, and not just the screen.

I guess I'm going to have to start learning how to build one like you guys then. Can't wait!

Docapi is correct but if you can get an old OHP for free it's still a good starting point and a neat toy.

Yeah, my mom is a teacher and they were replacing some of the older OHP so i was thinking that i could mess with one of those... maybe just get enclose it, and get a brighter light source. (which i happend to have)

Check out the site www.allinbox.com they have some diy projector using OHP.


Regards,
Traynor

What are the differences between the lenses you could get from stripping an OHP and buying the LL kits or elsewhere?

The lenses on an OHP are going to differ in a number of ways. First off, they're going to be smaller, if your LCD panel is larger than the fresnels from the OHP then you will need to buy new fresnels (unless you don't plan on using the whole LCD which would be weird). After that there's the grooves, I don't think different groove sizes make that much of a difference, but the fresnels sold here have a good groove size (or so they tell us). The last thing, and this one could make or break their usefulness: the focal length of OHP fresnels is usually 220mm and 330mm from what I've seen. If these are the focal lengths you need then you're golden, if you need different focal lengths then you'll need to buy new fresnels.

The projection lens has to be matched to the fresnels (don't ask me how the match making process works though). The 330mm fresnel would be find for the standard triplet, but would not work with the pro triplet.

Thanks Hirudin. But, I guess I was most concerned with the projection lense, as to whether it compared favorably to the standard lense. I had expected to buy new fresnels.

You should pick a couple up if you can/if they're cheap or free. They have parts you can use, especially for a small projector like what I'm working on.

In fact if you can get me specs for them I might steal 'em off you for a price.

If I'm not mistaken the triplet lens you find on better OHP models from Dukane, etc. is essentially the same triplet they used to sell on diyprojectorcompany, and differs from Lumen Lab's only in focal length. Many OHPs do not use triplets, though...

There is no real differance in a OHP and a LL PJ. We need larger fresnels just to cover the panels but the placement of all the parts is almost exactly the same. If you need to split the fresnels to to keystone correstion then you can do that too.

The main differance is the lamp but even that is not always that different. Some OHP have a HMI575 watt lams and some people have used them in the PJ's

The main thing is the stray light from not having the whole thing enclosed. The standard triplet we use is for a OHP. The pro lens is one of a kind.

Throw a LCD panel on the OHP for cheep. leave the light in it. add a fan to cool the LCD. Have Fun.