crt lenses for 7"Lilliput

[Doc B.]

I've been experimenting with good results with a Delta HD-8B lens from an 8" CRT projector. Seemed like a no brainer, seeing as the diagonal image on an 8" crt projector tube is going to be about 7". Turned out that coverage of the lens is quite adequate. The throw is a little short, but the f rating is probably well below f/2, as this lens is much brighter than an f/2.5 lens (Aero Ektar) that I was using before. I'm getting about a 96" diagonal image from the 7" Lilliput at about 8' from the screen. Should be no problem to get a 120" diagonal image in a typical living room. Getting even light across the screen was a little tricky, but I got it to work nicely with a condenser from Electronic Goldmine, two Staples fresnels stacked with grooves toward the panel and a third one closest to the panel with grooves back toward the lamp (a 400W MH). These fresnels are all stacked together behind the panel, about 1/4" away from it.

I had to buy three of these lenses and I only need one. I'm happy to offer the others to fellow Lilliput proj builders for my cost, $25 each, plus shipping for about 10lbs. The housings are a little bit dinged up, the front elements are very slightly scratched, and each lens is missing one of the lock nuts for the focusing adjusment. But they seem to project a clean image and the locking nuts are probably easily replaced with something from Ace Hardware. They are BIG, about 9.5" long and 6" diameter. If you are planning a tiny projector, crt projector lenses aren't the ticket. But if size is not an issue and brightness is, they seem to work very nicely with the 7" Lilliput and ought work great with a PSone LCD too. Forget using them with any panel bigger than 7", the lens will not cover.

 

[Mikey p]

Doc,
What is the distance betwwen the Delta lens and the LCD? Any chance of posting some pics of your projector?

 

[Doc B.]

Lcd - crt lens distance

Oh, it's really close, like 1/2" - 3/4". I presume that's the way the all CRT projector lenses are designed, to keep the overall length of the projector as short as possible. These crt lenses are big and long, so in the end the overall length balances out compared to OHP lenses, or photocopy lenses or whatever. The actual length of the projector to the front of the lens compared to the 7" Aero Ektar I was using previously (and which needs to sit about 5" in front of the panel), is about the same.

Unfortunately the projector is pulled apart right now and I have several paying projects taking precedence. I'll post some pics when I have a chance to to it put it all back together. My plan is to spring load the screws taht tie the lens to the panel mouting baffle so I can fine tune the focus at each corner.

 

[bochelie]

That's cool man. It is just the kind of the same idea that i have. But i want to use LED's to keep it small. (there are bright enough led's now)
I have some questions:
Did you put a fresnel between the LCD and the CRT Lens?
Can you make draw of the projector and post it?
Can you also zoom with lens?

 

[Doc B.]

You can see at the link below what I ended up with ( scroll down thw page when you get there). BTW, it's still available. I just got back from CES, and I can say that performance is similar to the cheapest DLP projectors I saw there - but with far less contrast. Considering how prices are coming down and quality is increasing in inexpensive commercial projectors, vs. the way prices are staying fairly consistent on LCD panels, I'm not so sure that the diy approach offers any real savings when you consider the performance you end up with. That's not to say the project wasn't exceptionally rewarding. I had a blast building the proj, I was forced to remember my physics and optics from college, and the result was very satisfying.

I stacked 4 Staples Fresnels together to get an even spread of light from the condenser, I put them right up against the panel, between the lamp and the panel. I couldn't stand the look of the image with a Fresnel between the panel and the lens. I can't remember the exact orientation of the Fresnels, but I think I had three with grooves facing toward the panel, and the Fresnel closest to the panel was facing the other way. The lens I used did not have much zoom capability, and the throw is pretty short. My proj ended up about 96" from my 93" screen.

If you get one of those Delta lenses in your hands I suspect that your dreams of keeping the projector small will end

http://www.bottlehead.com/loosep/docsstash/docsstash.html