Advice on small screens for Pepper's Ghosts

Escuta

Member
Joined
Mar 12, 2021
Location
Brazil
Hello,

I'm developing a theatrical installation that will involve a series of small Pepper's ghost illusions. The image sources are Amoled displays which give nice black backgrounds to videotaped actors. The reflective screens will be no more that a half square metre. The scenery will be panels and objects either back or internally lit with LEDs and there will be good dynamic control of the brightness.

Because of the close proximity of the viewer to the image, the reflective surface needs to be very thin to avoid double images - or if a thicker material is used, it will need to be treated in some way.

So far I've tested with kitchen plastic wrap and acetate sheets. These work but are tricky to maintain taut and could be a little more reflective as the Amoled screens are not particulrly bright. I read elsewhere on this forum that 'clear' or lightly silvered anti-UV films (the type used for windows) can be used to good affect in Pepper's ghost illusions. These also might be hard to maintain taut unless glued to glass or acrylic. In this case, what can be done to avoid double images? Would a light coat of dulling spray on the non-reflective side work? Or using anti-reflective glass of the type used in picture frames?

I should also point out that the budget is very low. So I'm looking for low cost solutions.

Any advice would be greatly appreciated!

Thanks
 

jtweigandt

Well-Known Member
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Aug 2, 2013
Location
Moline Il
I have to wonder if any double image might not give the illusion of depth? I would probably play with a thin glass or plexi first.
Lots of iterations of the "holographic box" on the internet mostly done with a pyramid of plexi, and viewed pretty close up.
Dr google is your friend here..
 

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jtweigandt

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Joined
Aug 2, 2013
Location
Moline Il
And here's the time Jenna Coleman from Dr Who dropped into my home workshop
Curving the plexi around the vertical axis gave her some depth
cheap LED projector back projected on slightly dusty plexi scrap
drwho.jpg
 

Escuta

Member
Joined
Mar 12, 2021
Location
Brazil
The viewer sees the image with both eyes through a large lens and with the ghost positioned at its focal point. The acetate I've tested with was slightly less than 1mm but, because of the micro-scale of the illusion, even this thickness gave a slight blurring of the image. In contrast, the plastic cellophane (considerably thinner) gave a much sharper image. The problem I'm finding, as mentioned in my post, is keeping such a thin screen taut. This is why I'm asking here about treating a thicker substrate. Also, plain glass, acetate and cellophane do not have the reflectivity that I would like. Thanks.
 
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jtweigandt

Well-Known Member
Joined
Aug 2, 2013
Location
Moline Il
The viewer sees the image with both eyes through a large lens and with the ghost positioned at its focal point. The acetate I've tested with was slightly less than 1mm but, because of the micro-scale of the illusion, even this thickness gave a slight blurring of the image. In contrast, the plastic cellophane (considerably thinner) gave a much sharper image. The problem I'm finding, as mentioned in my post, is keeping such a thin screen taut. This is why I'm asking here about treating a thicker substrate. Also, plain glass, acetate and cellophane do not have the reflectivity that I would like. Thanks.
It wasn't clear from your original post if you had actually tested an piece of thicker material like glass or plexi.... Its possible an out of focus second image might perform better than 2 very close focused images since you are using a magnifier with a focal point.. easy and cheap to test. You can also get various samples of silvered window film for windows and autos in varying densities..lightly silvered 2 way mirror if you will samples on ebay.. or one time I got a company to send me an end roll gratis.. they got excited when they heard it was for community theater.

They also make a film that can be applied to glass that is almost transparent but is used for window projections. I see samples on ebay for not a whole lot of bucks.. It's made for rear projection, but might keep as much light from reaching your second surface if used front reflection style. Look for holographic window projection or some variation thereof.
 

Escuta

Member
Joined
Mar 12, 2021
Location
Brazil
It wasn't clear from your original post if you had actually tested an piece of thicker material like glass or plexi....
Sorry, yes, I've tested 2mm acrylic, which gave a nasty double image.

Its possible an out of focus second image might perform better than 2 very close focused images since you are using a magnifier with a focal point..
It's not so micro-scale I think, the lens has a 400mm focal length, only a little magnification and a fairly mild depth of field effect within the scene - so won't help in this sense.

They also make a film that can be applied to glass that is almost transparent but is used for window projections. I see samples on ebay for not a whole lot of bucks.. It's made for rear projection, but might keep as much light from reaching your second surface if used front reflection style. Look for holographic window projection or some variation thereof.
I'll have a look, thanks, but with the local R$ the way it is, anything a bit specialised from abroad gets unaffordable.

Interesting that you say that the increased reflectivity of the film might diminish the double image effect from the second surface. Perhaps some of the UV blocking window films I've bean looking at will also have this effect. I'm looking for smaller sizes for testing...

I think I'll also try sk8rsdad's idea. Looks very practical.
 

Escuta

Member
Joined
Mar 12, 2021
Location
Brazil
They also make a film that can be applied to glass that is almost transparent but is used for window projections. I see samples on ebay for not a whole lot of bucks.. It's made for rear projection, but might keep as much light from reaching your second surface if used front reflection style. Look for holographic window projection or some variation thereof.
You're right, not so expensive, but unfortunately I can't do back projection, just reflection from an LED display.
 

tladuke

Member
Joined
Jul 7, 2013
Location
Orange County California
Hello,

I'm developing a theatrical installation that will involve a series of small Pepper's ghost illusions. The image sources are Amoled displays which give nice black backgrounds to videotaped actors. The reflective screens will be no more that a half square metre. The scenery will be panels and objects either back or internally lit with LEDs and there will be good dynamic control of the brightness.

Because of the close proximity of the viewer to the image, the reflective surface needs to be very thin to avoid double images - or if a thicker material is used, it will need to be treated in some way.

So far I've tested with kitchen plastic wrap and acetate sheets. These work but are tricky to maintain taut and could be a little more reflective as the Amoled screens are not particulrly bright. I read elsewhere on this forum that 'clear' or lightly silvered anti-UV films (the type used for windows) can be used to good affect in Pepper's ghost illusions. These also might be hard to maintain taut unless glued to glass or acrylic. In this case, what can be done to avoid double images? Would a light coat of dulling spray on the non-reflective side work? Or using anti-reflective glass of the type used in picture frames?

I should also point out that the budget is very low. So I'm looking for low cost solutions.

Any advice would be greatly appreciated!

Thanks
The large suppliers of film based Peppers Ghost use transparent polyester film (PET) . They like to sell this in giant rolls or only lease the system. High quality optical grade PET film is one of the best materials to use for PG. You would need to buy an entire roll and it can be found online in various widths up to around 60" wide but the roll cost would be prohibitive. You might be able to find a local graphics materials supplier to sell you several feet of the film at a low price. PET film thickness is measured in Mils. Something between 7 and 15 mils would work well for a small scale PG illusion.
Tensioning the film is not as hard as the big players claim. There is quite a variety of Peppers Ghost patents and most of them revolve around the tensioning technique. What nobody talks about is there are public domain solutions that work quite well for tensioning other thin materials including fabrics, polyesters, PVC, meshes etc. Something like https://www.fabricmate.com/shop/category/track-frame-2 This plastic extrusion uses a special tool to tuck the fabric in to the channel. The channel has small serrated teeth to grip the fabric. Take a 3" wide black GAFF tape material and put it around the edge of the polyester so it is folded over both sides. This requires you to measure and cut you material carefully to match the frame. I would strongly suggest a square steel tube frame. Use Tek screws to attach the plastic extrusion to the frame. Miter the corners where the extrusion meets. All of the fabric extrusion manufacturers have Youtube videos on how to attach the fabric to the frame and then tension it. They also offer the special "tucking" tool. It's a bit trickier with polyester but just take it slow .

The process of tensioning requires careful attention as you proceed. The smaller the frame, the easier it is. It is often assumed you need to really crank up the tension which is not true. You actually need very little tension. It's all about uniformity of tension. Corners will have puckering. Design your frame larger than you actually need. That way you have a "safe action" area in the middle of the sheet. If your completed frame is at 45 degrees to the floor, you may see a very slight deflection that can affect the image quality. You can address this with common video tools that can apply incremental correction to the image.

Wear cotton gloves when you handle polyester film. Tension your assembly on a flat table that has a low lint soft surface. Black Duvatine will work. Vacuum it first to reduce lint. Polyester has a nasty trait of attracting dust through static. Clean your assembly with a feather duster. Compressed air can actually induce MORE static and start attracting more dust so avoid that if you can. It is very easy to scratch polyester so handle with care. DONT use a heat gun on regular polyester. You will damage it and never get it flat. There is a class of heat shrinkable polyester. Rosco used to have a product like that but I don't know if they still offer it. You can buy heat shrink polyester aluminized mirror but that wont work for PG as it has very low transparency.

Good luck! Sounds like a great project
 

Escuta

Member
Joined
Mar 12, 2021
Location
Brazil
The large suppliers of film based Peppers Ghost use transparent polyester film (PET)
......
Thank you very much for an extremely informative reply, it's going to be very useful. Following on the suggestion by sk8rsdad, I found a local supplier of heat shrinkable clear PVC. It just arrived and it looks promising as it's very fine, clear and seems to have a glossiness about it. Have yet to test. I hadn't heard of PET but have found this locally too. Will try the PVC first as it's probably the easiest option for mounting. Great advice on handling. Thanks a again.
 
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tladuke

Member
Joined
Jul 7, 2013
Location
Orange County California
Thank you very much for an extremely informative reply, it's going to be very useful. Following on the suggestion by sk8rsdad, I found a local supplier of heat shrinkable clear PVC. It just arrived and it looks promising as it's very fine, clear and seems to have a glossiness about it. Have yet to test. I hadn't heard of PET but have found this locally too. Will try the PVC first as it's probably the easiest option for mounting. Great advice on handling. Thanks a again.

That sounds great. The shrink film should give excellent flatness and the glossiness should give you better reflection. Let us all know how it turns out.
 

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