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Discussion Starter · #1 ·
I just sent my X1 demo back to Infocus, but I will probably buy one. I'm now considering rear projection with the X1.


Where is a good place to get a first surface mirror cheap (I hear 90% reflectivety should be used for DLP)?


I'm wanting to go 90-96 inches wide with about 7.5-8 feet of space (distance between back of screen and where the first surface mirror will be placed) if possible. What size mirror would I need, and how far between the mirror and projector would I need?


Also, I'm not sure about the screen, but I found large 1.6 gain rear projection grey screen I could get for $125.00. Would this be good?


Basically I'm wanting to do this so we can watch with a bit more light during the day (since the X1 will be in a very dark space by itself), closer seating and a brighter pic.


It would be brighter right? Not just because of the screen gain, but wouldn't the shorter distance by using a mirror make the picture brighter?


If anyone here could help me with the please do.
 

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There's not much info out there on doing rear projection with these units, let alone the X1 in particular.


I'm afraid you may find brightness to still be a problem. I'm not that familiar with rear projection but don't you lose a lot of light because of the screen itself?


A 90 inch image requires the X1 to be a certain distance from the screen (13 or 14 feet or so) regardless of whether it's doing front or rear projection.


Try front projection and see how it works. You may need to go smaller than 90 inches but I was surprised how good the image is, even with significant ambient light. It's a little washed out, of course, but very watchable except for dark scenes.
 

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Just to be clear, I meant the light path from PJ to screen has to be 13 feet or so. All a mirror would do is redirect the light path. You'd still need 13 feet total distance so brightness will be the same either way (in fact it may be ever so slightly less using a mirror because of light loss/scatter.
 

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Discussion Starter · #4 ·
I don't believe you'd lose any light. I believe you gain brightness because:


1: The projector is in a dark black room with no light. It is enclosed it's own projection room basically while you are on outside with lights on. Not too much light, but a moderate amount.


I've turned the living room light on and watched my X1 projecting 17 feet away onto an 8 wide screen with pretty good results. I figured if I could get decent results doing that than having the X1 in a dark room using rear projection would make it look even better with moderate lighting.


2: The screen is designed for rear projection and has a gain of 1.6.


From what I've read a first surface 90-97% rear projection mirror is supposed to cut down the projection distance needed greatly. If I'm not mistaken they somehow make the throw distance appear longer than it really is. I may be mistaken, but I think that's what they do.


They are different than ordinary second surface (household mirrors) mirrors that would not reflect the same and would cause ghosting.


My 55" HDTV CRT aims at a first surface mirror which folds the light onto the 55" screen. The distance betweent the CRT and the screen is only about 5".


I'm not sure if I'm totally right, but I don't really understand what the point in a rear projection mirror would be if it didn't shorten the projection distance needed to obtain a certain size.


I've seen very small handheld first surface mirrors for sell to use with DLP/LCD projectors that increase the projection size upto 23%. They are fairly expensive though. Here's the link (although I'm looking for larger ones):

http://www.navitar.com/buhl/products_video_mirrors.html
 

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I think you have some confusion. The mirror just folds the light path, it doesn't change physics :D . If you need the projector 13' from the screen to get a desired image size, the light path from projector to mirror to screen is still going to have to total 13'. FYI, the Insight website has a utility for calculating this distance.


Second, rear projection televisions are brighter primarily because of the shorter light path. You set up your projector with a 5' throw and you'll be able to watch it in high ambiant light, it will just be a dinky picture.


Lastly the fact that the projector is in a dark area, is not the point. The issue is ambiant light within the viewing area and it's interaction with the screen. You have a certain maximum brightness for any screen to projector distance. The quality of the image will be directly affected by any ambient light in the room. Basicly, ambient light raises the floor of the visual noise level, reducing contrast. To use an audio example, in a quiet room you can hear all the music at a relatively low volume, move a party of 12 noisy people into the room and you need to significantly increase the volume to hear the same detail. That "12 noisy people" is your ambient light.


On first surface mirrors, as you noted, they are relatively expensive. In order to maximize their effectiveness in folding the light path you would need one near the "half way" point in the light path. This would require one significantly bigger than a small handheld mirror.
 

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Discussion Starter · #6 ·
Yeah, that's what I meant. I thought the guy was saying that the distance between the mirror and screen would still be the projector's distance, but I'm sure it was how far the projector was from the mirror and how far the mirror was from the screen. I'm just wondering what size mirror I should get., but I think I may have answered my own question.


One more thing. I found a two mirror setup rig where the PJ's light reflects off of one close mirror which then reflects onto another mirror above it, and the second mirror then reflects the image onto the screen. It said I'd only need about 5 feet to project a 100" diagonal image using this rig. It looks like what I need.


I'd hate to see the price on the rig though, but that's what I'm looking for. If I could only afford an 8 foot wide lenticular/fresnel (I'm guessing this is what I'd need to get the best possible image) screen I'd be in business.


Also, I'm aware that I'll need a fairly large mirror. I may try the two mirror route, so I may have to build a rig of my own.


I guess I'll just buy some stuff and do some tests. Thanks anyway.
 

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Please post any results from your testing. I was toying with this idea when I first got my X1 but gave up on it due to the concerns.
 

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I've seen a couple of links for sources for "first surface mirrors". Do a search in this forum on that criteria.
 

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The mirror rigs are extremely expensize and I dont know why it's only a steel sceleton with a mirror mounted, you can build your own rig of wood, the problem would be to mount the mirror so it can tilt. Keep things simple and stick to one mirror if you have the space.


some heavy price examples they coast more than the screen and projector.

DA-LITE Projector Screen Mirror System $4,399.00

http://www.dynamicsigndisplay.com/

Single mirror - Easy Erect Frame Only for a 67" Screen - £3942

PictureBox Retro Cabinet 67" - £8047


Jim Cavani
 

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For those prices you could buy a brand new RPTV & strip the mirror out of it. Actually, that's not a bad idea - buy a used RPTV, or even one with burned out guns from a TV repair shop, and use the mirror & discard all the other pieces.
 

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I think RPTVs also have better contrast because they resist light from entering into the projection camber but allow light to exit. If you look at a RPTV in the day, when it is off, the screen is black unlike a Front Projector screen which is white/grey. This allows the Blacks to still be black even in a well lite room.
 
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