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50/50 Mirror


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#1 Matthew B Clark

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Posted 07 November 2016 - 11:33 PM

Can I just use any simple square 50/50 mirror for some old school in camera effects?  I'm looking to build a rig that could use a 50/50 mirror and mattes to composite images in camera.  The biggest challenge is overcoming my own brain, which tells me, "Matt, there must be a 'special' 50/50 mirror that you need for this".  Any input or resources would be welcome.  Thank you.


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#2 Mark Dunn

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Posted 08 November 2016 - 04:47 AM

It's down to money. Any float glass mirror will be fairly flat, but you'd pay much, much  more for a ground optical flat. Take your pick.

http://www.customsci....com/flats.html


Edited by Mark Dunn, 08 November 2016 - 04:47 AM.

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#3 Phil Rhodes

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Posted 08 November 2016 - 04:50 AM

I've seen mylar film mirrors used in optical devices, too. Usually, they're stuck down to a fairly chunky metal precision milled and ground frame (to keep them flat).


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#4 Mark Dunn

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Posted 08 November 2016 - 04:55 AM

You have to be careful of the evenness of the mylar coating if it's more than a few inches wide. Ordinary sheeting can be pretty variable.

Of course if you can use a Pepper's Ghost arrangement you don't actually need a reflective coating at all.


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#5 Darrell Ayer

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Posted 08 November 2016 - 12:00 PM

http://www.stereoscopicmirror.com/

 

I was able to pick on up to do a blade runner effect, i have yet to build the thing but the glass was perfect, shipped in a great level of protection.


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#6 Phil Rhodes

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Posted 08 November 2016 - 12:34 PM

Did you find that the blade runner thing really needed 50/50 split, or could it have been less?


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#7 Matthew B Clark

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Posted 08 November 2016 - 03:58 PM

It's down to money. Any float glass mirror will be fairly flat, but you'd pay much, much  more for a ground optical flat. Take your pick.

http://www.customsci....com/flats.html

 

It doesn't have to be that high of a grade, but that's a wonderful resource to have.  I need about an 18" x 18" mirror that lets light in the backside (I've got wiggle room here, it can be bigger of course).  I need the sort of mirror that lets light in the backside, and also reflects on the front side, so that whatever's on the right side of the camera on the set easily composites back into the camera when the mirror is placed at 45 degrees from the cameras lens.  I'm building one of those boxes that has a pair of glass sheets with mattes on them at front and right sides, with 45 degree mirror between them, letting light in the front and reflecting the small scale set at right of camera back into the lens through a series of mattes that are made to counter the respective portions of each part of the composite image.  To do this, I know I need a two-way mirror, about 2 feet or so (to allow camera flexibility) but I need a cheap one, that just lets me get both parts of the image looking solid in camera.  Not like Peppers Ghost at all...which is all half transparent and "ghostly".  I need this to be two solid parts matching (for the most part) in camera, allowing small scale sets.  Schufftan style.  But I dont want to remove the silvering of mirrors, hence the box design and paper mattes.

 

I've seen mylar film mirrors used in optical devices, too. Usually, they're stuck down to a fairly chunky metal precision milled and ground frame (to keep them flat).

 

Would the metal back prohibit me using it the way I described up there?  I'm wondering what this would be used for, but this is a good thing to know about.  Thanks.

 

http://www.stereoscopicmirror.com/

 

I was able to pick on up to do a blade runner effect, i have yet to build the thing but the glass was perfect, shipped in a great level of protection.

 

Thanks for this link.  I checked it out.  Do you think this would achieve something like what I described up there?  Thanks again.


Edited by Matthew B Clark, 08 November 2016 - 03:59 PM.

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#8 Darrell Ayer

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Posted 08 November 2016 - 04:33 PM

Did you find that the blade runner thing really needed 50/50 split, or could it have been less?

I havent yet built it, but it was the most even loss. 1 stop to camera 1 stop from the light.  I just need to finish building it.  Im sure I will post it when I do. 


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#9 Darrell Ayer

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Posted 08 November 2016 - 04:50 PM

You would want a 50/50 for what you are attempting because you can more easily balance your exposures on both sides.  I would try to smaller in glass because of the $$$ and get closer to the lens..  shoot thru the mirror to your subject and reflect your miniature.

 

You can probably put a matte behind the mirror with a cut out for your subject and put a flag to block out the place on your minature so actors can be ^projected^ on it.

 

I bought a 4x5 inch piece and it cost 35 dollars so i am sure the 18x18in  will be quite expensive.  It is optcial glass so I don~t think you would have any issues with ghosting or refections, like you would with a regular mirror, it~s what was used to do this type of work back in the day.


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#10 Matthew B Clark

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Posted 08 November 2016 - 11:58 PM

You would want a 50/50 for what you are attempting because you can more easily balance your exposures on both sides.  I would try to smaller in glass because of the $$$ and get closer to the lens..  shoot thru the mirror to your subject and reflect your miniature.

 

You can probably put a matte behind the mirror with a cut out for your subject and put a flag to block out the place on your minature so actors can be ^projected^ on it.

 

I bought a 4x5 inch piece and it cost 35 dollars so i am sure the 18x18in  will be quite expensive.  It is optcial glass so I don~t think you would have any issues with ghosting or refections, like you would with a regular mirror, it~s what was used to do this type of work back in the day.

 

I set up my camera and tried out some lenses with a piece of paper simulating the mirror so I could calculate depth of field needed to capture both subject and the plane of the mirror.  It looks like I'm stuck with a huge mirror placed quite a bit aways from the lens from what I can tell using this depth of field calculator http://www.dofmaster.com/dofjs.html

 

It's going to be shot on Super 16 using 7265 black and white reversal, which puts me at 80 ASA and then I'm going to lose light with the mirror too, so I'm going to have to blast the hell out of that place with light to get into the middle of the lens, and probably because of these opticals, I'll have to scoot to the f/11 and f/16 end of things...

 

Anyway, the point is, I think 4" x 5" is going to force me to put the glass right on the mirror, and because the only lens I have that's usable here is probably a peleng 8mm, I think I'm screwed.  I have to figure out a size of mirror that will stay in focus with the subject behind it (10 feet away) and still cover the whole field of view of a Peleng 8mm lens on a Super 16 frame.  I also have a 50mm and a 135mm (which is absurd for this)


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#11 Matthew B Clark

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Posted 09 November 2016 - 12:01 AM

I had my girlfriend hold up a sheet of 8.5 x 11 paper using the Peleng 8mm, and walk it into the lens, and it covers the field of view at about 9" from the lens.  


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