[cmdang]

First of all, my primary thoughts are with the victims of this morning's atrocious terrorist acts, ourselves included. I plan to fly a flag at half-mast in front of my home today, once I figure how to jury-rig a flag pole.


I just received my NEC LT150 yesterday, and of course, I didn't sleep much last night, having played with my new toy & refusing to go to bed, until my wife threatened to shut down the power. I enjoyed it very much right out of the box, running it via my PC, although I was jumping around with different media & didn't quite watch an entire movie.


The layout of my family room has made me think of projecting the image by reflecting it off of a mirror (the idea was suggested in the manual; not my original idea). I can think of three advantages: 1- the pj remains in front of the room, where the rest of the AV equipments will be, so there will be less cables/cords snaking around 2- the throw distance is increased with less space 3- I can mask the mirror directly, to help avoid the halo etc..., instead of masking the screen (which is actually only a white wall at this time); I can also make a mask for the 16:9 to avoid the letter box effect on the final projected image. These thoughts haven't been actually carried out by me.


Has anyone tried projecting off of a mirror, and what are your thoughts/experience, even if you haven't tried it?


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Michael

 

[Huckster]

Random thoughts -


The mirror will get dusty/dirty unless you account for dust/dirt.


There is other light leakage coming from the projector's vents that needs to be tamed if you are going to place the projector at the front of the room.


Where will the center cannel speaker go and will the mirror cause problems with the sound?


Most rear projection TVs (RPTV) use a first surface mirror to reduce visual aberrations caused by shining light through the glass. I would look for some scrap RPTV mirror material and use that.


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Huck

 

[tim_f]

If you put the projector in front of your room and beam it off a mirror to the screen the mirror will have be half the size of the screen.


EXP: 100" (40" x 80") screen you need a throw distance about 14ft. The projector is in front of the room the mirror about half the distance 7ft. The mirror size needs to be about, guessing here, 20"x40" half the screen size. And with the angle of the mirror it would be in your way.


A mirror is great for shooting your projector from an angle, that way the mirror is closer to the projector.

 

[RF1031]

People do it all the time. I've even had a mirror move into place rather than using a projector lift. Draper uses a similar approach in their revelation model mirror mechanism.

Use a first surface mirror. Do search to find sources. These reflect from silvery front of glass not the back of glass to avoid difraction problems.

Every rear screen TV uses them. It is a tried and true method just make sure the glass doesn't bow at all or you will have your own hubble telescope.

(dust isn't much of an issue. Just follow manufacturer's directions.

Randy

 

[cmdang]

Thank you all for your input, especially regarding first-surface mirror; being a very fresh beginner, this is the first time I've heard of it. I have ordered one already.

I tried it with just a regular mirror at home, and it turned out surprisingly acceptable, although I did see minor glare artifact from the thickness of the glass; the first-surface mirror should take care of this. The dust particles weren't much of an issue; I deliberately left the mirror very dirty. As to my setup and for my purpose, no, I don't need a mirror half the size of the screen. I set the projector on the coffee table at the end toward the wall/screen, and the mirror at the opposite end. The distance between the pj & the mirror is to maximize the width of the mirror, which is roughly 14"; everything was level on top of the coffee table -- no angulation/tremendous keystoning necessary for my coffee table height. My plan is to built a simple open wooden platform with the pj at one end and the mirror slotted at the other end; in front of the mirror slot will be another slot to slide in a mask to take care of the halo on 4:3 image or another mask to take care of the letter-box effect of the 16:9. (Or I could just tape off the a 4:3 frame on the mirror itself, and make a 16:9 mask.) The advantage of this setup, for the specific layout of my room, is that the projected image is larger than anything that I could get from simply placing the pj on the coffee table, and once done, I can simply take the platform off of the table -- I don't have a permanent AV room. I haven't tried the mask, so don't really know how that will work.



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Michael

 

[dreamer]

Michael,


That actually sounds like a very reasonable arrangement. I think originaly people were assuming you wanted the mirror on the back wall of the room. Building the whole arrangment into a coffe table would leave you with something similar to the first "projection TVs" where the front of the TV pulled out into the room and contained a mirror that bounced the CRT image back onto the front surface of the screen.


I can see how your arrangement could improve your throw by several feet using even a 14" mirror. In this arrangement, the mirror itself should block any light-spill from a viewer sitting in the middel of the screen width, but what about people sitting off to the side ? Isn't their view of the lens going to be annoyingly in their peripheral vision ?


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*********************

Kirk Ellis

G1000 D-ILA, HTPC, Panamorph (soon I hope),

Dish 6000 (HBOHD,SHOHD,CBS,NBC,ABC,WB,FOX,UPN, KCET -- does it get any better ?)

 

[cmdang]

Thanks, Kirk, for pointing out the problem with the lens shooting back at the viewers. Maybe the "wooden platform" has to be much better designed than I had envisioned, with perhaps side walls and such. While I'm at it, I should also build a hush box at the pj end of this platform.


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Michael

 

[Morbius]

Michael,


It won't be "a mirror" - but "mirrors".


Remember, depending on the orientation of the mirror

to the projector - each reflection is going to flip

either top/bottom or left/right. So you need an

even number of mirror flips to maintain parity.


Even if you have a PJ that can be hung upside down - in

order to hang upside down the projector has to flip both

up/down AND left/right. So it does the equivalent of

2 mirror flips - so the number of real mirror flips also

has to be even, even if you use the upside down option.


Greg

 

[jkaiser]

I am not sure what mirror you are planning on using, but

for reflecting images - front surface mirrors are preferred over back surface mirrors. front surface mirrors, like those used in Newtonian telescopes have the reflective material, usually silver, applied to the top side of the glass. Your garden variety of hall mirrors have the silver on the bottom side. The problem is the light or image has to pass through 2 layers of glass with a back surface mirror, which can lead to distortions. Also the quality of the surface is going to matter. A 20" by 40" would have to be over an inch thick to be stable.


As far as reflecting the projector straight into screen, baffles inside the case can usually overcome most of this.

 

[noah katz]

It would be an odd number of flips (FP counts as one reflection), but in any case virtually any projector can reverse the image to compensate.


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Noah

 

[Morbius]

Noah,


Yes - if you count the reflection off the screen - it is

an odd number of flips.


If count the number of mirror flips - and hence the number

of mirrors - that number is even.


Greg