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projecting on mirrors
posted by Andrew Milmoe (andrew@milmoe.com, www.milmoe.com), 02.03.2004, 20:09
»» »» Does anyone have any experience in projecting on mirrors?
»» »» I am working on a project where I need more specific control of the
»» »» projector/DVD placement and have been mystified by the physics of my
»» »» experiments. Is a front surface mirror neccessary? Would love to trade
»» »» info with other artists or scientists who have ideas.
»»
»» You can aquire inexpensive front surface mirrors of a decent quality from
»» companies that sell stained glass supplies. I purchased some that were
»» approx. 8\" x 10\" for $17.
»»
»» By the way, the main benefit is that you will not have the second ghost
»» image from the glass. Think of a rear view mirror in a car... If you flip
»» it one way you see the reflection in the mirror which is brighter than the
»» (in the flipped mode) reflection in the glass. The rearview mirror is
»» actually a prism where the front surface of the glass and the mirror
»» surface are a few degrees from parallel. When you bouce a projection off a
»» traditional mirror you get a second ghosted reflection from the glass..
»»
»» -Andrew
Thanks Andrew,
I did figure out about the front surface mirror, its a big improvement.
The double reflection is not acceptable for projecting on a sculptural
object, the image gets blurred too much.
Have you ever heard about a half surface mirror? None of my suppliers
knows about anything like it. I'm now looking for something to project
on that will allow the viewer to see themselves in the back side of the
mirror as well as having the projector project on the front of it. Any
ideas?
Best, Lillian
-------------------To which Andrew replied:
Hi Lillian,
You may want to investigate teleprompters and half-silvered mirrors. Here is a place to start:
http://science.howstuffworks.com/question421.htm
You could position it so that the viewer sees themselves reflected in the mirror, and then the video projection would appear on a standard projection surface inside of a black box... imagine a picture frame with the half-silvered mirror on the front surface and the projected image on the back surface. If you used rear projection then the half silvered mirror and the rear projection could probably be right up next to each other.
You would need to carefully control the lighting so as to balance the half mirror image with the projection... to much of one and the other disappears.
If you wanted to build a prototype you could use mirrored mylar sheets from industrial plastics on Canal and a sheet of frosted glass. You could even try frosting the back side of the mylar with unscented Right Guard deodorant spray. (Not a permanent solution, but it's a cool trick for a one night installation.) Once the deodorant dries it creates a pretty even and very white frosted surface... just be sure not to touch it or you'll have a giant finger print on your projection surface.
You'll still need to isolate the video side of your surface so that no ambient light shines on the back side of the projection surface. It will soften the contrast of the video projection and the reflected image of the viewer.
The high end, permanent version of this would be a sheet of half silvered glass that is frosted on the side that is not half-silvered... this would have to be custom done... they could probably do it cheaply at Urban Glassworks... they have a sandblaster. Just keep the "sticker" on the half silvered mirror side while they sandblast the other side.
Hmmm, that sounds cool. Let me know how it turns out.
-Andrew
---------------------and then Lillian replied:
Dear Andrew,
Thats a couple of nifty web pages you sent me, could come in handy for all sorts of things.
Well actually, I have done a lot of mirroring. I've had things blown and done quite a bit of blasting at Urban Glass. They don't mirror but I have a guy that does if you ever need it. I did it once but its not that easy or fool proof .
I think the general concept you suggest may be possible. Its tough to explain this because the piece already depends on a mirror for the projection and rear projection is not possible. Its all open so you can see everything. Imagine a mirrored glass 3D sculpture on the wall, the projector is inside it, it projects out to a front surface mirror which throws the reflection back on the sculpture. I want the mirror to do both- reflect the viewer from one side and reflect back onto the sculpture on the other. There is a 4 ft distance between the sculpture and the front surface mirror.
My hunch is that the half mirroring will not be strong enough to reflect back on to the sculpture and that the projection coming out of the sculpture will be too bright and blind the person looking at it. But I'm going to give it a try and experiment (I like the trick with the deodorant.) What does the frosting / sandblasting do but diffuse the light?
Thanks for your help. Did I meet you at the ASCI meeting the other night? Christoff wants to have us use the bulletin board but it seems much simpler to e directly.
Best, Lillian
---------------------And then Andrew replied:
We probably met, I'm the guy who works with Ben Rubin at EAR Studio.
The frosting/sandblasting would create a projection surface, but if you are projecting back on to the sculpture that's probably not the effect you want.
Let me make sure I have this right though... The user is looking in to the projector and seeing themselves and the projected image on the glass, as well as seeing through to the reflected image which is on the sculpture?
If this is the case then you want a half silvered front surface mirror, with the mirror side facing the sculpture. If you frost the glass side the viewer will see more of the "projected on the glass image" and less of themselves. With too much frost they will not see themselves at all.
If you frost the half silvered mirror part then the viewer will see themselves, and the projected image on the glass, but less of the light will reflect back on to the sculpture. (a lot of it will scatter.)
I think you'll end up having to just carefully control the light. The more you cast on the viewer the more they will see their own reflection.
You'll probably want the background behind the viewer to be as dark as possible so that they are not also seeing reflections of the walls instead of the sculpture.
And one last thing... if you don't want the viewer to see the image projected on the glass at all then skip the frosting altogether. I may have misunderstood. In that case you can just use a half silvered "two way" mirror like they use in cop shows.
Hmmm...
-A
--------------------and finally Andrew replied...
Andrew,
The sculpture is the projection surface. The piece is actually done, its just that now I feel it would be so much better if the viewer could not only see themselves but see themselves "inside" the projected image. Let me explain how it is right now in this way.
O > < I Io > Viewer
O is the sculpture. The 1st I is the front surface mirror and the 2nd I is the also reflecting back of the front surface and the o bathroom mirror it is attached to. Front surface mirror appears to be mirrored on both sides. Perhaps its just easier if you had a chance to see it. I'm around the corner from where the meeting was in Tribeca if you want to stop by.
What I want to do is have the viewer is looking into the mirror and seeing themself and the same projection that is reflected in the sculpture. I don't really want them to see the projector light beam. And they can see the projection on the sculpture from any number of points around the piece already.
My supplier says there's no such thing as half silvered front surface mirror and doesn't recommend sandblasting because its too delicate. He doesn't even recommend cleaning it. But I tried lightly sanding the front surface and putting that toward the projector and you can see a slight reflection. I also tried sanding the back or glass side and that also seems to work with less of a direct projector beam coming through. I'll have to fiddle with the light sources and see how that effects things.
I'm reading a book on magic and can't seem to get Pepper's ghost out of my mind.
Thanks for your help,
Lillian
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projecting on mirrors
projecting on mirrors