2 Ideas for OHP/Panel Combination

Hi Guys,

I'm new here... I looked into DIY video projectors about a year ago and just checked into it again yesterday - WOW the hobby has really come a long way!

I'm interested in building a basic OHP/LCD Panel combination but I have a couple of ideas that I haven't seen yet:

[1] When I watch movies I like to have it *completely* dark just like a theater. The OHP is going to put out a lot of light, normally, so I wonder if it's possible to construct a pyramid shape (with the top chopped off) out of sheet metal or something to block out most of the light. I want to use a high output OHP like the Elmo HP-A305 Solar Deluxe or something that will be *really* bright... So there could be a potential problem with reduced heat dispersion from my shroud - although I don't know how much heat would normally be dissipated through the glass anyway. Does anyone know if this would be a problem? Maybe it would be remedied by a small computer fan installed on one of the pyramid faces?

[2] I have a fairly small living room so my couch is pushed all the way back against the wall opposite my entertainment system. There's no place to put the projector behind the couch. I thought I might mount the projector on *upside down* on the *ceiling* as a semi-permanent installation. Does anyone know if there would be any problems running an OHP upside down? I would guess the only moving parts in the unit would be the fan(s), so I can't think why this wouldn't work. Another possibility would be mounting the projector sideways.

While I'm here I suppose I might ask another general question. I want to get the full resolution (or close) out of my DVD player projected. I read that DVDs store 500 horizontal lines of resolution. A lot of guys are using VGA (640x480) panels, but in widescreen mode wouldn't that drop you down to 300 lines or so because of what gets chopped off the top and bottom? I'm thinking an SVGA panel (1024x768?) might be the best choice if you really want to get the full picture from your DVD... am I on target here?

Whoever replies... thanks a million.

-Schmanthony
 
Hi Schmanthony,

On a correctly aligned OHP with a decent LCD panel, you would get some benefit in light reduction, but nothing monumental. With one of the high-powered designs like the Elmo 305, you would have cooling problems, though... (The LCDs are temperature sensitive and require free air flow.)

As for panel resolution - by all means - if you can find a source of cheap high-res panels, buy one and let us all know too!!! :D

Bill.
 
Light reduction and resolution

Woneil,

Thanks for posting that reply... so maybe you wouldn't mind explaining why the light reduction would not be significant. I would imagine that the majority of "unused" light would be coming from the glass on the top of the OHP in a normal configuration. I would assume that some light would come out from the side(s) of the unit where there would be a fan and an intake/exhaust vent, but that this would be drastically less than the amount of light coming from the top.

My shroud would block all light coming from the top of the unit except the light that is actually used to project the image.

So are you thinking that the amount of light from the sides of the unit are significant, or even greater than the light coming from the top?

As for the potential cooling problem - are you are saying that the LCD panel will have the bulk of those troubles and not the projector? Is this not something that could be remedied by one or two computer fans installed into the shroud (leaking some light of course - hopefully not much).

What about mounting the overhead projector upside down on the ceiling? Do you think there would be a problem with that?

And about resolution again... am I on target for a 1024x768 panel being necessary to capture the DVDs ~500 line resolution effectively in widescreen mode? Isn't everyone using 640x480 panels building a cheap projector but losing a lot of their DVD's resolution?

About the cost... It seems entirely possible to buy a high output projector and high resolution panel for less than $1000 if you're willing to settle for quality used components, am I wrong? Am I also wrong to assume that the quality of this projection from a DVD source would rival a new $3K-$4K LCD projector out of the box?

Maybe somehow I got way off base here and there's something I'm wrong about. So please don't worry about putting me in my place and (maybe) prevent me from doing something stupid!

-Schmanthony
 
A little more resolution research.

I believe I've determined that XGA (1024x768) is overkill for use with a DVD source over an s-video cable.

According to this website:

http://www.unitedvisual.com/2faq/2faq1.asp#LCD

"The wider bandwidth [of an s-video cable] translates to a horizontal resolution of about 400 lines compared with the normal 240 to 320 lines with conventional composite video connectors."

So it looks like the s-video cable itself is a weak link and will knock your DVD signal down to about 400 lines. (Still good, though.)

At the "widest" wide screen ratio of 16:9, I calculate that an SVGA (800x600) panel will give you 450 lines of resolution - (9/16 * 800 vertical lines) - sufficient resolution plus a little "breathing room" for the signal you'll be getting from your s-video cable.

Does anyone concur that XGA (1024x768) would be a waste of money for use with an s-video connector, and that a good 800x600 display would be a far wiser choice?

-Schmanthony
 
Schmanthony,

In a properly set-up (decent quality) OHP, the vast majority of the light coming out of the top of the LCD will be pre-beamed by the fresnels under the OHP's top-glass into a cone of light whose apex is at the OHP objective lens.

Most of the light SHOULD get projected onto the screen this way.

Even in a good design, there will be some light hitting the ceiling, but you will probably find more leaking out from under the LCD, and through fan holes etc.

If you want to put a shroud from the top of the LCD panel to the OHP objective then it should be ok, but make sure that the vents in the LCD panel are not blocked, and that there is an unrestricted free flow of air between the top plate of the OHP and the bottom of the LCD.

Nasty things happen to LCDS that get too hot.

Upside down shouldn't be a problem if things don't fall out... :) (many OHPs are intended to be kept upright, and things can literally fall out (at least of alignment) if they are tipped upside down.

As for resolution. Remember that in the US, at best, a DVD is stored on the disc using 720x480 resolution. For a 4:3 image with square pixels, this translates to 640x480 - strangely enough, the same resolution of the LCD panels... ;)

For Anamorphic Widescreen DVDs played on a screen with square pixels, you would benefit from greater resolution - to get the correct aspect ratio with square pixels, the 720x480 image should be scaled to 852x480. Thus, even with 800x600, you are still losing a few pixels.

My own personal choice is to still use square pixels and tell the dvd that I am using a widescreen projector - but then use an anamorphic lens to compress the image vertically... That way, the 640x480 4:3 screen still works!

Having said all that, I also have a 1024x768 projector that displays perfect images when fed from my computer... It is very noisy though...

Overall, the best value combination can be had for $150(ish) - a 640x480 panel driven by a decent OHP driven by a computer - no side-effects from interlacing/macrovision/3:3 pull-down etc.

Check out the other threads for much valuable detail.

Basically, most DVD films are adulterated by the players to get the 24fps progressive film image onto a 30fps interlaced tv screen. Most computer DVD players will play the image in its native format without needing to translate it to NTSC and then back to VGA again...

Bill.
 
Changes to my plan... and a few more questions.

Woneill,

I've changed several things in my plan... many due to things you have said, so thanks!

I haven't bought anything yet and I'm taking my time. I'm very excited at the prospect of a decent resolution, *bright* projector for <$500.

I decided to mount the projector right smack in the middle of the rear wall just high enough over the couch (which is all the way up against the wall) so that your head doesn't crash into it when you go to sit down. :) I'll build a special shelf for it.

I decided against an upside-down ceiling mount because I realized - in addition to all the trouble of suspending everything - it's probably going to create a substantial keystone once the beam is angled down to the level where my screen will be... I have a 9 foot ceiling, and would like my screen to be eye level when sitting down.

I've also decided against my shroud in favor of a large wooden box to put the whole thing in. I'll put vent holes in the bottom of course and probably a duct fan from home depot ($15-$20) on the top. Should block a lot of light leaks and I can probably pad the inner walls of the box with some sort of sound-deadening material to make it quieter. Most of what I'll be hearing will probably be the duct fan. Hmmm - maybe I can find a quieter fan than that. Hopefully some sort of AC powered flush mount fan.

More questions...

[1] I like the idea about the anamorphic lens with a 640x480 panel... but is this applicable for OHP projects? Is there an anamorphic lens I can find that will easily install somewhere in the light path? (Or is this going to be a big DIY headache that I'm not looking for?)

[2] I do not want to use a computer in my setup. I will be using a regular DVD player. Should I assume Macrovision *will* be a problem and expect to need one of those s-video to VGA converters? ($80-$100) If this is the case, perhaps I need not bother looking for panels that accept s-video, since I'm going to have to go to VGA anyway?

[3] If I buy a high quality, shielded s-video cable - one that's 50 or 75 feet long to stretch from my entertainment system over to my projector, will I get noticeable image degradation from the length of the cable? Would it be worth moving my DVD player over to the projector and running a 50-75 foot optical audio cable over to my receiver instead? (More work...) Or should I move my *whole* stereo system back to the projector and run ALL the speaker wire all over again? (A lot more work...) The long s-video cable route is the simplest and if it will be OK on the quality that's the way I'd like to go.

-Schmanthony
 
50' s-video or 50' vga?

One more thought I'd like to tack on to that last question. If bridging a 50' gap with a good video cable *can* provide acceptible quality, would it be better to go 50' with a long s-video cable or with a long VGA cable?

Seems like cost isn't a factor as both 50' cable go for about the same. Would one provide better results than the other?

Maybe if I'm using a video processor/scaler of some sort like what would be required to eliminate macrovision, it would be better to plug that into my DVD with a short s-video cable and then run its VGA output 50' over to the panel.... hmmm.
 
40' TOSLink

In a thread I started in the "Digital" forum about TOSLink cables, someone answered my question about bridging that 50' gap...

Placing the DVD by the projector and running 50' of TOSLink cable across my living room is the way to go. Either s-video or VGA video will degrade over that length. But TOSLink will either work or not - it's an all or nothing thing, apparently - since it's digital. The person said that TOSLink will work up to 25 m, or 82 ft.

I think I can get away with 40' of TOSLink. I can buy 2 20' lengths and a F/F TOSLink coupler for less than $50. About $20-$30 more than what I'd spend on that length of video cable, but I think it's money well spent for no loss in image or sound quality.

It's lonely over here. Nobody loves me. :(

-Schmanthony
 
Hi Schmanthony,

Macrovision WILL be a problem with most LCD panels. That is why most people are using the decoders.

However, the output from a decent PC (>500MHz) will be significantly better than virtually ANY hardware DVD player under $1000. Using a PC is my preferred way of doing things.

(Even if you have a slow PC, there are the Sigma decoder cards that use a special MPEG-oriented DSP coprocessor to accelerate things available new for < $100...)

You mentioned Keystoning. That is not a problem if you can control the positioning of the LCD panel relative to the lenses.

To shift the image without keystoning, simply move the lcd around so that its center is not at the center of the fresnel. (Or move the position of the lenses relative to the LCD.) As long as they are all aligned along parallel optical axes, you can shift the projected image without keystoning being an issue.

Bill.
 
Agreed a PC DVD player is the best way to go. I tried my DVD player with an ATI tuner card running dscaler and then compared it with my software DVD player. What a difference it made in quality. All the fuzziness and other problems were gone. Although I'm still going to run dscaler for my TV purposes. If you are worried about digital sound you can simply use a sound card that has digital outs on it. My sound blaster live has digital out port and I got that couple years ago for $50 OEM version. BTW I got my DVD drive yesterday for 60$ at Best Buy yesterday well actually it will be $20 after the mail in rebate :). It is a silent drive which was one thing I was concerned about. Seems relatively speedy and it includes a full version of powerdvd 3.0 with it. Awesome program which allows you to stretch the aspect ratio a little bit. Also a software dvd player looks a lot better then a tv tuner when turned up to higher resolutions. I changed my monitor res to 1600*1200 and still got perfect frames.

HTPC:
Intel Pentium III 533 mhz
Sound Blaster live
16x Pine DVD drive
512 SDRAM
60 gig Western digital HD
ATI Radeon 7200
 
computer = extra clunk and extra $$$

problem is.... computer is in the computer room, the "office" if you will, and the "theater" is in the living room. Like most folks here I'm on a budget with this project and to buy another computer with a DVD player would be a significant cost and easily turn my $500 project into a $1000 project.

Not to mention, my OHP/Panel will be mounted over the couch right above the viewers heads. Where would the computer go? It would be just another big clunky thing that would suck power and make noise. It would also be a little weird to have to boot the thing up and use the mouse every time I want to watch a movie. I want to just turn it on and go, you know? I want it all sealed up in simple, nice looking box... I want to use the same remote to pause my movie whether I'm watching on my TV or my projector... I could go on and on.

How do you guys pause the movie if you're using a computer to run the DVD? Do you have to hit ESC on the *keyboard* and drag the *mouse* over to the on-screen pause button? That's kinda silly, isn't it? I want to just hit *pause* on my *remote* like I do normally when I'm putting my feet up and sprawling on the couch.

Nah.... I hear you about the quality and scaling and macrovision avoidance and stuff but a PC just isn't going to fly for my project.
 
There are lots of remotes that interface with pc's. And it's not esc it's space bar most of the time :) . I don't need to pause my movies very often plus I have a wireless keyboard that I can use. With dscaler you can even pause live tv with its experimental timeshift feature. My pc is fairly quiet and I plan to run it 24/7 with it going in standby when not in use.
 
I`m with you Schmanthony. I would kinda like to do this pc-free. I can`t afford to buy another computer just for watching movies. Not with all the other stuff I have to buy. This is getting expensive. :)
I take it from all the replies that a the TV-3000 decoder thing is almost a must if not totally a must with a panel, is this correct?
Toodles!
 
TV-3000....

I do have the TV-3000....but there are much more products than that one that might been even cheaper...I took a chance when I ordered it not knowing if it would fix my macrovision....Lucky for me it worked....The TV-3000 gives you added brightness/contrast/tint/saturation control....now it lists for like $99 ...so it's little higher than other products that do the same I bet...but it comes with cable connector to hook up your cable for television and a remote control to vhange channels...for more products kinda like what I have here is a link

http://www.avtoolbox.com/video-to-vga.htm

...I just do not want people thinking that the TV-3000 is the answer for all....there are more products out there that might be as good or even better and may be cheaper...

as for the route of going from dvd player to panel you WILL need something to stop the macrovision...

-blockhead
 
Elmo on his way...

Well, my project has officially begun, and I've officially spent money. I won my Elmo HP-A305 Solar Deluxe on Ebay last night. I'm excited... working on the panel now. Looks like there are money-making opportunities out there, lots of people selling panels not knowing what they have, writing lousy ads on ebay, selling items as untested that, when you ask them to perform simple tests afterwards, seem to be at least partly functional...

I might buy a few panels with the intention of using my favorite and reselling the others.