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Front Projection - Project and materials

Front Projection

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#1 Alessandro Vasapolli

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Posted 18 October 2013 - 12:48 PM

Hello,

 

my name is Alessandro Vasapolli and this is my first post on this forum even if I have been following you for a while.

 

I am trying to set up a front projection stage but, being it the first time I do it, I have many questions...

I have tried to read all I could and I tried to look online as well but I could not find answers so please excuse me for the, maybe, obvious question that I will make...

 

So, first of all the material for the screen...

On another post here on cinematography.com (that I can't find anymore) I have found out that the material should be the 3M Scotchlite High Gain Reflective Sheeting (7610) but, speacking with the rapresentative here in Italy they did not know what I was talking about...

Also, on the PDF that I have found, it seems like that the only possible sizes are: 1/2 in. (1.27 cm), 3/4 in. (1.90 cm), 1 in. (2.54 cm), 2 in. (5.08 cm)...

I guess there is an error or how do you make a screen out of it?

 

The second question I have is regarding the mirror used to reflect the light from the projector: how big should it be (my screen will be approximately 3mt * 3.5mt)?

Also, here in Italy seems like that all the beamsplitter mirror also reduce the lights on both sides as they are mainly used in buildings as glass for the windows. The commercial name of what I have found is "stop-sol".

 

I think that's all for now but I'll surely come up with more questions once I'll hear your answers so thank you very much in advance for your help!


Ale

 

 

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#2 Mark Dunn

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Posted 19 October 2013 - 09:23 AM

7610 used to be available to special order in wide rolls- about 18" IIRC- and is then applied horizontally in strips from top to bottom overlapping slightly. It is very expensive, though- twenty years ago it was several hundred pounds a roll.


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#3 David Mullen ASC

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Posted 19 October 2013 - 11:01 AM

The mirror would be right in front of the camera lens and projector lens so I don't think it would have to be that big, maybe in the 16" x 12" range, but that's just a guess.

 

Yes, front-projection screens are made up of strips glued together -- if you look at the blu-ray of "2001", you can now see a mosaic pattern in the sky in the Africa sequence.


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#4 Phil Rhodes

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Posted 19 October 2013 - 11:35 AM

Could this not be done with the screens produced by Reflecmedia for chroma-key work using the blue LED ringlight?

 

I'm not sure if it's designed to behave in the same way as 3M's products, but as far as I'm aware, retro-reflective is retro-reflective. In fact it may actually be a 3M product rebadged.

 

It's certainly available in large-ish single piece sheets. Try contacting Reflecmedia.

 

P


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#5 Alessandro Vasapolli

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Posted 20 October 2013 - 06:12 AM

Hello,

 

thank you very much for all your answers.

I have contacted 3M representative here in Italy and I waiting for his response.

 

So I just have to make strips, vertically, and glue them together? How big should be the overlap?

Also, shall I put them on a frame or create a boards structure behind?

 

On the VES book I've got a bit confused because in a paragraph entitled Front Projection Equipment (Characteristics of the Retroflective Material) they say to cut the material in a hexagonal or diamond shape. Also, why do they refer to retroflective material if we are talking to front projection? (maybe here I am missing something in translation...)

 

Thank you very much


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#6 Alessandro Vasapolli

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Posted 23 October 2013 - 03:22 PM

Hello,

 

I had a response from the 3M rapresentative in Italy and he told me that this material is not available in Italy in the 18 inch format but only in narrow strips.

Have you got any ideas about where I could buy it in the US and than have it shipped here?

 

Thanks a lot,


Alessandro


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#7 Carl Looper

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Posted 09 December 2013 - 02:39 PM

The material is designed to reflect light back along the incident angle with the same efficiency regardless of the angle the material is with respect to the light source. So it's not necessary to have the material perfectly flat across the surface. It can be overlapped (introducing bumps) that don't affect it's efficiency.

 

However it's not 100%. So if you apply it in strips you are risking the introduction of very faint seams from bumps in the overlap, or far worse: gaps between the strips. And if those seams are straight lines (as they would be) the more visible they would risk being.

 

So the better method is to actually cut the material up into random shapes and apply it to a surface in a random overlapping pattern. Any faint changes in efficiency caused by variations in the surface normal (through overlap) are statistically neutralised and otherwise very difficult to perceive.

 

C


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#8 Francois Lanciault

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Posted 10 December 2013 - 10:11 PM

Hi,

 

I use Scotchlite series 680. A couple of years ago it came in 48 inches wide rolls, it might still be available, I did not check. I still have an unopened 48 " x 80 " roll for my next project.

 

The series 680 was nice because it has no large "lens" as can be seen on some other product (like the ones used on highways) It is made of evenly distributed .006" glass beads.

 

Even though you loose light shooting in a beam splitter, it is the way to go. Remember Scotchlite materials are best used when the camera is perfectly in line with the projected image. Their performance degrades quickly if your off just by a few degrees.

 

Good luck!

 

François 


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