I was wondering, based on a couple posts I saw where folks took 2.5" screens and popped them into a slide projector or pvc tube without using fresnels, perhaps it would be possible to make a similar type of PJ based on a slightly larger panel. To do this, I was thinking of using a 5" panel like for the PS1 or maybe one from here...

http://www.aeicomp.com/Detail.asp?Product_ID=003.100_LCD5PAL

Then add a projection lens intended for CRT projectors like this one...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...5771938564&rd=1

Then all that would be needed is an appropiate lamp and a parabolic reflector to get the light parallel (parabolic reflectors seem easier to get than hemispherical). The reflector would have to be sized a little larger than the lcd but that shouldn't be too difficult.

I don't know if this would really be simpler (seems like it would be from an optics/alignment point of view) or more compact (which I was hoping for), but seems like it should work just the same.

Any comments? (sure, tell me I'm crazy and those crt projector lenses won't work )

No one here has done that to my knowledge, but I think someone over at diyaudio did that. I think that it worked. Here is at least one person's attempt at it. I guess he isn't around there anymore. Link to DIYAUDIO page

That seems like a neat idea to try. If it worked correctly, the projector would indeed be smaller. It would eliminate the ~320mm needed between the lcd and the front lens.

[edit: I am pretty sure that it is near impossible to make a projector as small as he is showing right now, but you would eliminate the 320mm mentioned previously.]

CptPower,

Thanks for the link. That does look like what I had in mind, only the LEDs were a bit of a surprise. Too bad it looks like he abandoned the forum before posting some pics (if he was ever able to get it working right). The really great thing about this type of setup would be the compact form factor coupled with excellent range for throw distance and screen size. Pretty darn low cost too considering how cheap the lenses are on ebay and the cheap small lcd screens. And for the optical alignment impaired like me, less stuff to align means easier building!

Thanks again!

I love the idea! Having a larger aperture lens means we'll not have to worry about etendue and we'll have better throughput. Just a matter of finding the right CRT lens. It's easy to get em' cheap for 7" CRT's as they are very common along with some of the smaller ones.

I bought a nice CRT lens on ebay for a total of $21 a couple of years ago...never used it for anything...so, I'm really curious to see how this works out. Keep me posted for sure!

one thing to watch out about is the short throw distance ment for the crt lense and adjustment for keystoning. I have been trying to find the time to do this project for awhile now but cant seem to find it anywhere! Maybe with this forum i can give myself a swift kick in the butt and get motivated

You're definitely right about the throw. I held the lens in front of a 13" tv and pointed it at the wall in a dark room. For the projection to be in focus, the lens had to be right next to the TV screen. At a distance of a few feet from the wall, the projected image was at least 6-7' diagonal. And of course, the 4" lens cropped out all but the center of the image on a 13 inch tv.

Still, I don't see any reason why a small lcd shouldn't work with it. I was thinking that it would be a neat project to mount the whole works in a 6" diameter PVC tube...and make a bazooka looking projector. A couple of plant hooks and chains or a tracklight channel could serve as a ceiling mount....or even a mic or portable light stand like for photography could serve as a mobile unit.

Of course, one question I have is how good the picture looks from a 5" PSONE lcd when blown up to 72-100".

Eric

i took my psone 5" totally unmodded and simply held it up to my crt lens awhile back and got a decent projection.( mind that it was very dim, like could barely see bright scense with all the lights off) and that got me interested. all one needs to do is build a "super backlight" that EVENLY illuminates the lcd. I think it would be pretty difficult to build this to be veiwable in anything than total darkness.

tonight i tryed out the old 500W halogen work/flood light. i think the brightness could work but the heat of the 500W halo is just to much (not to mention a safty hazard)
my next thought is to use a couple of those energy star flourecent light bulbs with a reflector of some assort.

Keep me posted on your experiments. I have considered the very same....flourescent daylight bulbs in an array as a backlight. After all, that's what's in these LCD backlights...just an array of fluorescents. The main difficulty as I see it is to get the light diffuse enough for even lighting without knocking the output way down.

If that can be done, it would eliminate one fresnel, leaving just the forward fresnel to focus the image onto the projection triplet.

I've been considering a set of those small tube fluorescents in a tightly packed array, with no gaps between tubes....but I'm not an electrician of any kind and am not sure about wiring and ballast for this sort of thing.

My other interest is in the high output LED array....

Not an easy thing to do.

I foresee a number of problems.

Number one: Heat. (ie how to cool it?)
Number two: Colour temperature.
Number three: Getting them close enough together
Number four: The ridiculous number of ballasts you will need
Number five: The uneveness, which will probably be very visible on the projection, since the array of lamps will be in focus.

I dont know how many of these are valid points, but I think you have quite a task on your hands if you want to use fluorescents!

As for LEDs, this has been discussed a kajillion times before. There are many threads about it, all coming to different conclusions, but you might want to check out http://www.lumenlab.com/forums/index.php?showtopic=6722.



ukagr, you cannot use a Compact Fluorescent bulb with a reflector because it is not a point source.

Hauntman's idea doesnt need a point source because he eliminates the need for the first fresnel.

I am looking at doing a project like this, I bought a 4" LCD and a 4" HD-6 CRT projection lens. My LCD, though, can't be stripped. Just found this out tonight.

Does anyone know if the 4" Liliput LCD panel will strip? I'm not too stressed about buying one that won't strip, but shelling out for a second that I couldn't use would certainly irritate me.


Thanks,