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post #1 of 60 Old 03-08-09, 05:13 PM Thread Starter
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Mirror Experiments

Mirror experiments is something else that I'm going to attempt to get started this week as well. We all know that using a mirror as a substrate will help reflect more light back. But how much light? And how much paint negates the reflection of a mirror? Also what are negatives of using a mirror as a substrate?

I have a bunch of 12" square mirrors that I will be spraying and rolling. These are 3mm thin mirror tiles. One of the things that has come out and all experts agree on is that using a mirror as a substrate will cause a slightly distorted image. I can believe that this will be worse for people using a 1080P projector. Why does this happen? The light is diffused through the paint and then reflected back to a different location than where it entered. Make sense? Hopefully the experiment will yield some useful information.

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post #2 of 60 Old 03-08-09, 05:13 PM Thread Starter
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Re: Mirror Experiments

The paint used for both this and the translucency experiments was Valspar Ultra Premium Flat Enamel White or VUPE White.

Rolled


The tray, roller, roller cover, and paint weighed 988 grams before starting. After one coat on a mirror it weighed 982 grams. Meaning 6 grams of paint is used per coat on a 12X12" tile.

The thickness of the mirror without paint on it was 2.72mm. It was supposed to be 3mm. After one rolled coat it measured 2.93mm for a difference of .21mm. Meaning one coat of paint gives you roughly .2mm thickness of paint.

I used no water with the rolled paint. I used a 1/4" nap roller.

After curing for 5+ days the thickness of the painted coats has settled some.

Paint Thickness

Miiror with no paint 2.72mm
w/1 rolled coat 2.83mm
w/2 rolled coats 2.91mm
w/3 rolled coats 2.99mm


Sprayed


Paint Thickness

mirror no paint 2.72mm
w/1 sprayed coat 2.76mm
w/2 sprayed coats 2.78mm
w/3 sprayed coats 2.80mm
w/4 sprayed coats 2.83mm
w/5 sprayed coats 2.86mm
w/6 sprayed coats 2.89mm

Keep in mind that I did a spray an initial frost coating to help the paint stick better to the glass. Here's what that looked like:



Data coming soon.
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post #3 of 60 Old 03-08-09, 05:13 PM Thread Starter
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Re: Mirror Experiments

Data

[PIE]The amount of light measured (incident) at the screen coming from the projector was 15fL for 100IRE and 3fL for 50IRE. I used both a 100IRE and a 50IRE windowed image to get measurements.[/PIE]







Some photos

On the left is the reference white hardboard panel - to the right is the 1 coat sprayed mirror





shuffled them around so you could see the tags



A Black Widow mirror tile up front!




Conclusions

These readings initially shocked me as I really thought that a mirror would produce a brighter image. That's why I had Harp recreate what I've done and asked him to confirm what I've found. Well, he did! Now the question is why. The obvious answer is that paint is nowhere near translucent enough to allow light through to hit the mirror. That's confirmed by the translucency experiments. The answer to this elsewhere is to add polyurethane. we all know this would be a terrible decision as polyurethane yellows rather quickly requiring new paint on a yearly basis. And you don't want to keep adding coats to that $$$ mirror you bought! In the past I did some work with a clear protector that showed promise. Harpmaker and custard are also working with other mediums that may offer themselves up as a 'translucency helper'.

Light fusion (mirrors) as it stands now though is busted by the screen mythbusters!
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post #4 of 60 Old 03-08-09, 06:04 PM
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Re: Mirror Experiments

Quote:
mechman wrote: View Post
One of the things that has come out and all experts agree on is that using a mirror as a substrate will cause a slightly distorted image. I can believe that this will be worse for people using a 1080P projector. Why does this happen? The light is diffused through the paint and then reflected back to a different location than where it entered. Make sense? Hopefully the experiment will yield some useful information.
Right, the thicker the mirror the worse this effect will be. It could look very similar to "ghosting" on analog TV's. In theory, a front-surface mirror would not have this effect since the actual paint layer would probably not be thick enough to cause it; but almost all common mirrors are rear-surface so the light must go through anywhere from 1/16 to 1/4 of an inch of glass before it is reflected back, and it must again go through all that glass before it leaves the mirror on the way to your eye. The glass forms a sandwich between the paint and the reflective surface.
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post #5 of 60 Old 03-08-09, 06:04 PM
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Re: Mirror Experiments

Quote:
The light is diffused through the paint and then reflected back to a different location than where it entered.
The thinner the mirror the less the image is distorted, correct?

Edit: Don posted the same time I did and answered my question.

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post #6 of 60 Old 03-08-09, 06:43 PM Thread Starter
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Re: Mirror Experiments

Yep thinner would be less distortion. How I'm going to show this will be interesting. I'm planning on just taking some macro shots with side by side materials - one with mirror as a substrate and the other using the foam board I use as test panels. The thing is with mirrors is that they're so expensive.
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post #7 of 60 Old 03-08-09, 06:48 PM
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Re: Mirror Experiments

Expensive, yes, but the results can be awesome from some of the "test shots" I've seen.

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post #8 of 60 Old 03-08-09, 08:39 PM
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Re: Mirror Experiments

It may be possible to reuse the mirrors for other test mixes by removing the dried paint with Xylol/Xylene. I discovered it worked well for removing paint from PVC and even tempered hardboard without damaging the substrate. I don't believe it affects plexiglass either, but I'm not sure.

We'll know more after mech does his tests, but as I currently understand it, painting on mirrors is a very tight balancing act; too little paint and the image is too bright and has a very narrow viewing cone; too much paint and the effect diminishes to the point where it looks like a painted wall.
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post #9 of 60 Old 03-09-09, 02:52 AM
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Re: Mirror Experiments

Nice experiments.

I have also experimented with mirrors as substrate. As you said the picture gets "smeared" the thicker the mirror is. But, as in my case with my SONY VPL-HS60, I have rather exstencive screen door effect, so it actually improved my pic from that point of view.

What I did was to use a plastic laminate used for obtaining "frosted glass" look. I would say that this might be a very interseting way to go, if it weren't for one thing. Hotspotting. We need to increase the thickness of the diffusing layer untill the hotspotting disappears. I believe that a mirror substrate screen is easier to get to work if you limit the size of the screen, that is from a hot spot point of view.

I curious thing I noticed. The 3M invisible sticky tape I use for fastening paper and stuff on the glass generated by it selfe a nice picture ! Imagine that!
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post #10 of 60 Old 03-09-09, 06:51 AM
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Re: Mirror Experiments

Has anyone tried using first surface glass mirrors or mylar mirrors like they use in many of the better RP sets?

Looking for me, just google my username. I have used the same one for most sites for many years.
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