Opaque projector optics, a few newb Qs.

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Ok, forgive my newbness, but ill never learn if i dont ask.

ive searched, and ive read. NO ONE EVER FLATOUT ANSWERS/SHOWS RESULTS of a projector using opaque projector optics. Im not looking to do the lazy way, and just lay an LCD on the spot where the paper loads, im lookin to shine right thru the LCD. i know otherwise, i will probably get reflection.

I read that its possible to get an image with something as low as flourescant bulbs? i know those arent ideal because theyre brighter at first, and they have more of a blueish/white tint. I dont really care about that. Im going for a pretty short distance, not a huge screen...40" or so.

What im going for is, something small i can use in my room, which is about 12 feet wide. I got a new fishtank and i hardly watch TV, except for gaming and movies so i figure ill save space and make a projection setup.

what else is just as powerful? i think its pretty impressive you can project a peice of paper using a 150watt light bulb. Would the optics from those cheapo 50$ onea that take like a 7"x7" object work? Im figuring on only using a small 5"-7" LCD.

Im aslo assuming, you guys dont just call em OP optics, are there another name for the lenses? Triplet for one, but when you refer to triplet, does that mean its as powerful?

I know the F-stop is pretty low on them, like what, f1.5?

Lastly, lenses from RPTVs, is there any use out of them?

Sorry for my newbness, thanks in advance.
All kinds of options...

OK, opaque projector optics are great, you've just gotta have a really long throw distance. My Opaque projector lens has an 18 inch focal length. I don't know what the f-number is. My 5inch diagonal Sony PSone lcd projection was bright, clear and sharp but only about 2 feet wide on my projection screen 13 feet away. Hardly worth the effort. Obviously I hadn't done my homework to find out what focal length I needed. I did find a great calculator to help though, at lightshow .

A lot of people will say that a fluorescent bulb won't work, but I built a light box out of acrylic mirror and put a 55 watt (a real 55 watt, not a 55 watt 'replacement') full-spectrum compact fluorescent bulb in it. No ballast was needed, it is built into the light bulb. The thing cost 30 dollars, but it put out enough light to make me happy. And it is rated for 8000 hours. By the way, fluorescents do put out some heat at higher wattages, so you will need a fan. My lcd started to turn black after about 25 minutes with no fan.

As far as f-numbers go, remember the higher the f-number, the less light per unit area reaches the focal plane of the screen. In plain english, an f2.8 lens will give you an image four times as bright as a f5.6 lens for the same size image. An f1.4 lens will be sixteen times brighter than a f 5.6 lens. No joke. Now you know how I can get away with using a fluorescent bulb.

Lastly, I think that the lenses from RPTV's are great because they are from f1 to f 1.4 most of the time. The big drawback is the limit on the size of lcd you can use. They are designed for 5 inch diagonal or less, and have to be close to the lcd, within an inch or so.

Hope this answers some of your questions.

oh heck yes!

this very muchly answers alot!!

i live on ebay, and opaque projector parts are now really hard to find. RPTV lenses however are always on, and when garbage picking we always run into these darn things. Lotta times they work so itd be a shame to steal the lenses.

What you made is exactly what im looking for!

Try using a UVB bulb, theyre spiral shaped. Theyre BLINDING! i dont know what the output is, my gf has one though, without any shades around it its ungodly. We dont use it on the lizards anymore, we were afraid it damaged their eyes. doesnt give off that much heat either, its used for the light to help growth.

i just checked, she said theyre in the gardening section of home depot. but doesnt know the wattage/lumens.

when i saw the green spots it burned in my eyes, i immediatly ran over to feel it wasnt that hot..and the dim lightbulb in my head turned on, projector!

and even moreso, i am making a visit to my old photography teacher. She constantly finds assorted old lenses. Most of them are for medium format enlargers/cameras, however, she does have 1 large format enlarger. Its the size of agarbage can and has a 220 line on it. wonder if i can take a look see.

this helps alot T, thanks
No UVB for me

A UVB bulb may be bright, but it is precisely the wrong kind of light to use for lcd projection. Everyone is always looking for a way to protect the lcd from ultraviolet light because it just destroys the lcd. I'll stick with my high output compact fluorescent bulb.

Yes, I use a full spectrum high output compact fluorescent bulb. The socket and bulb are about 8 inches long, so "compact" is a relative term.

I use just one lens, the tv projection lens. It is f1.0 with a focal length of 102.4 mm. The projector sits pretty darn close to the screen.
The 2 foot image was from that opaque projector lens with a 18 inch focal length. That sucker is in a cardboard box right now. I don't know what I'll do with it.

The RPTV lens is the one I'm using. It has the 102.4mm (about 4 inch) focal length. Much better, bigger image.

ok thank you. that helps, ill probably hit up ebay for an RPTV lens. you saved me a ton of hassle.

btw do you have a link to your projector on here?

Im gonna go the flourescant route, however there was 1 member on here that used LED's, however he fell off the face of the earth and never finished his projector. He was using an RPTV lens, and i beleive he showed some damn nice results. Maybe when i get my first couple projectors going ill pickup where he left off.

thanks for your help T.
I don't have a link to my projector here, but since my digital camera is a 20 dollar special, I'm going to sign out the one at work for the weekend.

I'd like to take pictures of the RPTV lens projector, and I made one of those 2.5 inch lcd (playstation hip screen) and slide projector projectors. If the pixels weren't so huge I would watch it every day, it's so bright.

You wouldn't happen to know where I can find a 640 X 480 really small lcd, would you?

Well, ebay is my first guess for anything. How big? im assuming nice and small?
If you mean pulling out of soemthing, most older Hi8 cameras have that kind of resoloutioon, the flip out screen i mean.

ive been meaning to experment with one of those projection LCDs, the older ones are all 640x480.

If RPTV lenses produce such great results, why dontmore people use them? Seems to me its alot cheaper, and it makes sense you get a nice huge image easily.
small color LCDs

These guys have a lot of small color LCDs, and controllers that can drive them:


That big 18" fl opaque projector lens will be perfect when you decide to build a 15" LCD-based projector. You can get a 15" LCD monitor with excellant specs, for less than $200 these days. MY 15" projector is hooked up to my DirecTV box with an S-video-to-VGA converter, and it is like watching 1024 by 768 HDTV, but in 4:3 format.
I've been looking at lcds from camcorders, and most of them have lousy resolution, and there is the added problem of finding a way to input the video signal when the camcorder itself doesn't have any auxiliary video inputs. Some of the Canon minidv camcorders have audio and video inputs, but I'm still not happy with the lcd resolution. And of course, there is the price.

Speaking of price, wow, earthlcd is not cheap, and the resolution of the smaller ones they have isn't good. Worth a try to look at though.

The reason RPTV lenses aren't more popular with DIY projection enthusiasts is that you have to use an lcd whose diagonal isn't larger than the diameter of the lens, or the corners of your projection get cut off. We all want the best resolution lcd's we can find for projection, and I guess too many people aren't happy with what a psone lcd can give them. Also, the max screen size you can get in focus with an RPTV lens is usually around 50 inches diagonal. Everyone wants a 100 inch diagonal screen.

I will really envy you if you get that f/1.0, 5.25 diameter lens. That will be just about perfect with a 5 inch lcd. Ooooh....


Not to rain on your parade, or anything...but enough LEDs to make a decent image would cost way more than a MH lamp & ballast kit. (Like 50 times more expensive.) They would also generate MORE heat than a MH, since their efficiency is lower.

Those high-intensity LED modules are nothing compared to a 250 Watt MH lamp. MH lamps are incredibly bright, and the only thing more efficient is one of those yellow or pink sodium parking lot lamps.

Just recently some manufacturer has come out with an LED-powered projector. It makes images in the 15" to 20" range. Commercial projectors use a trio of unfiltered LCDs, light recycling, and a bunch of other fancy tricks to get much higher optical throughput. With DIY techniques, your LED-powered projector would be limited to tiny images in a completely dark room.

Many DIYers have spent lots of time and money on LEDs, but the threads always end before they post results...
Yup, so ive read. Its the dream we all chase. That one guy CLAIMED he had great results, then disappeared before he would post any. Im willing to bet that was just to tease everyone.

Anyways, im looking for a pretty silent projector, probably with this f/1.0 lens im looking at. T. says he gets decent results with flourescant, whcih i would probably use..its jsut for my bedroom..however, if MH gives off a similar amount of heat id go that way.
Ok, question, seeing since these lenses have an amazing light aperture, but were limited to an LCD the size of the back opening, is it possible in any way to use opaque projection and and mirrors/lenses to cram like a 7" lilliput in there?

I only ask, because im not liking the whole limitation factor before i get screen door effect. Im currently trying to investigate the PS2 LCDs that are 5", and seeing if theres a guide out there to hacking one up, also with tech specs.
the limit is the short focal length

These wide CRT projection lenses all have very short focal lengths. The distances between the object, lens, and screen image, are all described by:

1/lens focal length = 1/object to lens + 1/lens to screen

So if you move the lens closer to the screen, then it will focus on an LCD that is further from the lens. If the screen is close enough, then a 7" Lilliput will probably be far enough from the lens to work. Of course, "close enough" might be way too close, with an image size too small to make you happy.

Another approach: Extend the focal length of the projection lens by adding a weak negative lens. Then the LCD would be further away from the lens. surplusshed.com has some big negative lenses for $4 to $6. Might be worth an experiment, to see what kinds of distortion this introduces to the image.

Wouldn't it be nice if you could get a 5" XGA LCD with fast response time and high contrast ratio? Then we could make really great tiny projectors using CRT lenses.
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