I have completed my first multitouchtable and simply used a normal mirror to
enlarge the image onto the projection surface. Unfortunately, the image is
has that ghost effect around sharp edges. I was wondering what kind of mirrors
all of you use. I know that you can get rather expensive mirrors especially
made for projections, is there a cheaper alternative?. Maybe some kind of foil?

thanks for any help!

tim

Hi Tim,

I have experienced the same problem as you did. I did a lot of experiments with different reflective foils, like the gold and silver safety blanket made from NASA mylar (Bill Buxton believes in this method for making mirrors, I’m not!!) and foil used in building scalemodels for airplanes (called Oracover). Non of these resulted in an acceptable mirror. I ended with buying a 3mm thick normal mirror which seemed to work almost perfectly. When the background color of the projected image is dark in relation to the details, the ghost image is slightly visible.  With this knowledge i make sure that the background color is not getting too dark in order to avoid the ghost image.
Later I heard they also sell surface reflective mirrors on a base of some sort of a polymer (probable acryllic or something more rigid). These mirrors should be available at your local glass-store. They are much cheaper then a glass front surface mirror but I haven’t tested these yet. Maybe the image reflected on such a large mirror may get distorted by the more flexible base compared to a glass mirror.

If you found a way, please keep me updated!! But don’t waste your time by experimenting with foils on large surfaces.
Good luck

Gr Arjen

I am just using a plain old flat mirror tile, without any issues

In holland I think we had the same problem, of ghost images, but that was probably because the image on the acrylic reflected back on the mirror and back on the acrylic again, at least that’s what they thought. We ripped of an everyday mirror from a wall in the mens room.

In sweden we also use an cheap ass every day mirror, but it doesnt show ghost images.

I wouldnt go with special foil or whatever, just find some cheap mirror anywhere and test it

Thanks for all of your input!
I tested a special mirror from my school (made for projections), and the diefference is huge!
Clear, no ghosting, perfect contrast… unfotunately its really small, so I can´t use it for my
project. Well I´ll keep searching. I´ll do some searching for a better solution and keep you updated
on the results.

tnaks again!

tim

today we did some testing with our prototype and we also encountered ghost images when we use a very bright projection (for example a white background on windows), but we were able to remove the ghost image by adjust the angle of the beamer, so the ghost image wasn’t projected on the acrylic, but on the wood underneath it.

Anyway there are also special surface mirrors that prevent ghost images, but i have no clue on prices etc.

ok, I talked to the guys who made the tangent table last year. They studied the same thing I do (Ineraction Design in Zurich). Anyway,they used
a special type of reflective foil/mirror used for projections. Its pretty expensive and the problem is that they are pretty big (way to big). And you
can´t just cut them, otherwise the foil will get ruined. I´ll see how the didi it, and post the results… The funny thing is, everytime I talk to some
Audio Video Dude and tell them that I want to use a plain mirror for a beamer projction, they right away tell me that it won´t really work well because
of the “ghosting”. They tell me I need an “optical mirror” which are really expensive (about 200-330 Swiss Franks for my size).

@gravano: yeah I noticed that too, but somehow I haven´t found the right angle I guess It´s a bit better, but not satisfactory for my project..

Does anyone know what type of mirror is in the back of a RPTV set? I was just thinking about some of my 50” 1080p DLP’s here and how there only 13” deep (even less distance from the lens to the mirror on the back of the set). I know quite a few repair men and TV enthusiasts in my area that I could probably get some for close to nothing. I don’t know how well these mirrors would work though. If I didn’t care about these sets, I’d rip one of these suckers apart and replace the screen with an acrylic and cut a camera hole in the rear and turn it into a nice encased multi touch screen.

Yes, it’s called a first surface mirror or a front surface mirror. You can get them off ebay or from optics places. When the light passes thru the glass it creates the ghost images due to refraction. Having a first surface mirror fixes this.

Ok, I got my new “optical” mirror today!
I order it from a webshop in Germany ->http://www.screen-tech.de/ Product is called ST-AV-HS
Actually its not really a glass mirror, its a reflective foil thats attached to an aluminium frame (like an canvas).
I bought the smallest on (50 x 50cm) which should be enough for most table setups. I cost me 100 Euros plus shipping.
The image is really incredible! Sharp, no ghopsting, awsome colors and high contrast. So if you can, I would buy one
of these… I´m extremly happy!

I just ordered this foil FS mirror as Tim suggested, but I would like to know if anyone in Europe have tried some DIY solutions to make an FS mirror.
I’ve tried two mirrors and a paint stripper, but the paint stripper is not strong enough to strip the back of the mirror without the need of scraping.
Even though it is the strongest stripper I found and it is for car paint, having methylene dichlorid as composant but still not strong enough. Or the painting on the back is just made to survive an atomic blast.
As far as I know Aircraft stripper is not sold in Europe since it is a too aggressive chemical. So its kind of prohibited.
So what do others use here in Europe to strip mirrors?

Thanks
Greg

i haven’t tried it “yet” making a diy fs mirror.
but i saw it on a how to from a diy beamer forum
i got a link to it : http://www.lumenlab.com/forums/index.php?showtopic=21137&pid=260751&st=60&#e;ntry260751

bit i think you have already been there…
i suggest some search true the lumemenlab diy fs mirror topic maby that some Europe people tried it and found a solution ?

please tell me if you find a paint stripper that works
(im a European to )