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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.

Digital Caliper



Scale

 

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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. :huh: 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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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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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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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. :spend:
 

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

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Has anyone tried using first surface glass mirrors or mylar mirrors like they use in many of the better RP sets?
My guess is yes, that someone has tried it. They've been playing with mirrors for quite some time at avs. I think the big problem with them is that you can get a commercial solution, that is more than likely a better solution, for a cheaper price. When I was pricing out a mirror 3+ years ago for a 100" screen they were running around $180.

I looked for first surface mirrors at a couple of home improvement stores. But I couldn't find any. :dunno: That would be the best solution though. :scratch:
 

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I found some very interesting sites that sell mirrored mylar. The stuff is cheaper than I thought, but since it is thin it would have to be mounted in some manner.

The first site only sells 1 mil film, but it is 54" wide and seems very reasonable in cost.
http://www.planetnatural.com/site/reflective-mylar.html

The second site is a bit more expensive, but offers thicker mylar and also has instructions and fasteners for making a portable mirror out of the film. They sell 1, 2, 5 and 7 mil mylar.
http://www.mirrorsheeting.com/

I just searched for "hydroponic reflective mylar" (without the double quotes) and these sites were on the first page of results (I used the Clusty.com search engine).
 

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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.
This is how I made my original ultra high gain screen..Acrylic mirror with a clear Matt Acrylic overlay..
The problem with this type of screen (as you mentioned) is the severe hotspotting..
Increasing the thickness of the "frosted glass" type Acrylic, only adds to the image distortion..
The only way to control the hotspotting is to curve the screen, so the hotspot is spread across the screen..But then you will still have some light fall off at the sides..
The other thing is that this type of screen produces very high gains..in the order of 8.0+, which is way too high for most modern digital projectors..
I originally designed this type of screen, to be used with low lumen CRT projectors..
 

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I found some very interesting sites that sell mirrored mylar. The stuff is cheaper than I thought, but since it is thin it would have to be mounted in some manner.

The first site only sells 1 mil film, but it is 54" wide and seems very reasonable in cost.
http://www.planetnatural.com/site/reflective-mylar.html

The second site is a bit more expensive, but offers thicker mylar and also has instructions and fasteners for making a portable mirror out of the film. They sell 1, 2, 5 and 7 mil mylar.
http://www.mirrorsheeting.com/

I just searched for "hydroponic reflective mylar" (without the double quotes) and these sites were on the first page of results (I used the Clusty.com search engine).
Harp..Whilst these films are excellent as a first surface reflector, they are almost impossible to laminate to a substrate without some creases or irregularities to the finished surface..and any flaws in the surface will be clearly seen in the finished product..
And as mentioned above, they cannot be used in a flat screen with the right amount of translucency to the top surface material, as they hotspot terribly..
 

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Hi Prof. Nice to meet you.

I see youv'e done some research. Curved surface would spread the spot, yes, I understand.

But when I say that one could increase the "frosted" thickness, I meant in the sence of increasing the optical difraction. For example I took a sheet of printer paper and saw the same "smearing" effect once I put it on top of the mirror, ableit it was significantly reduced. On the other hand the "gain-effect" almost dissapeared. So I was thinking one could use thinner paper.

Or you are sure that the mirror principle is a dead end?
 

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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!
I've been smack dab in the middle of this debate many times! :)

Robert what you just said is probably what was the biggest benefit of using mirrors back then. Also in the day, projectors back then were not nearly as bright as they are now unless a person is using a presentation projector and not a dedicated HT projector.

SDE can be greatly reduced with this method because the light is being diffused and refracted and coming back at different angles and with lower energy. This causes a slight image blur, but usually not so much that it becomes disconcerting to view. It does though cause the pixels to fuzz out and blend together which reduces or even eliminates SDE (depending on the projector and screen size of course). Also is the brighter image on axis, and again back in the day with the lower lumen projectors it was an acceptable trade off for some.

Too much refraction though and we start to get color shifting. This mainly shows up in white areas or when the screen is mostly one color and there are panning shots. The cost vs actual performance has always been the debate. It is by far the most exotic type of screen out there, but also the hardest to make as well as the most expensive DIY option.
 

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Has anyone tried using first surface glass mirrors or mylar mirrors like they use in many of the better RP sets?
I know mylar has been tried. It is definitely much cheaper than buying 4'x8' mirror, but it can be hard to work with and get stretched tight. It's also pretty thin and spraying is the only way to go, rolling flexes too much.

Another alternative is aluminum. I have five gallons of Black Jack 5168 and just found a source for more in my area so I'll be up to twenty gallons (hopefully by the end of this weekend!). Aluminum is often used to make mirrors, and it is used as the mirror coating inside CRTs. What intrigues me with this over something like mylar is it's just as inexpensive (maybe even moreso) and can be applied to anything. The big problem though... I seem to be the only person that can find Black Jack 5168!

Rose Brand sells mylar mirrors premade, but they are pretty expensive in my opinion.

I never really was a 'fusion' guy myself, mainly because it just doesn't work the way some try to explain it does. Then again, some people are still stuck in a rut over neutral grays and some are in a big hole trying to make a neutral gray out of red, blue, and green. It can be done, but the real question is why do it? Anyway, those last two were off topic in this thread.

The big question mech and I have mulled over for a couple of years now is when does the effect of the mirror diminish as the layers of paint are applied. I've seen demonstrations of mirrors and yes they can produce incredible on axis gain, but the cone is so narrow that even moving one seat over and the brightness starts to noticeably drop off. It is a very tricky balancing act that's for sure. If it truly is the best of the best, I always wondered why we've never seen this featured in any HT mags out there. They always love the exotic and expensive and I highly doubt that screen companies haven't thought about this themselves as a screen option, but ultimately dropped the idea.

I did run this whole concept past the profs at RPI and RIT and they thought it was interesting but ultimately said there were too many negatives to it and they disagreed with the forum version of how and why it is supposed to work and if it even works in a practical sense.
 

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Then again, some people are still stuck in a rut over neutral grays and some are in a big hole trying to make a neutral gray out of red, blue, and green. It can be done, but the real question is why do it?
I think you should have said that 'it can be done, just not the way they are trying to do it'! :bigsmile: I believe Harp said it would take 2 weekends to fix that mix. I think it would take much less. And don't forget the yellow which none of the Michaels stores in my area carries. :rolleyes:

Back on topic. I've got a few things to purchase after work today and then tomorrow will be a day of rolling/measuring/spraying. Hopefully I'll have a start on the results Friday. :T
 

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Mech if I pick up those two five gallon containters of Black Jack... now that the weather is warming up I'll send you a quart. If you spray it on the back of a piece of glass or plexi you'll have yourself an inexpensive second surface mirror! Plus it's a great thing to test out first surface mirror theory with.

Or... people could just use BW, it is loaded with aluminum so it basically has a mirror right in the mix ;)
 

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Sounds good Bill!

So here's the plan...

Three mirrors for three rolled coats.

Six mirrors for the six sprayed coats. The initial sprayed coat will be a dusting and not be measured.

  1. Thickness measured for each.
  2. Quantity of paint used measured for each.
  3. Reflected light measured for each - both on axis and at 30 degrees. The constant will be a ~10X10" hardboard panel with the same paint on it.
  4. Image quality determination via macro camera shot
Am I missing anything?
 
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