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Beam Splitters


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#1 Brian Alan

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Posted 17 February 2012 - 02:09 PM

Does anyone know of a beam splitter available with a prism behind the lens?


Old Bolex cameras used to use them for the view finder. Working on a project and I was researching the idea. It wouldn't be for 3D purposes at all. Actually it's for something a little more experimental and a new effect/idea (and no it's not HDR).

Any information would be great. If I have to create my own I'm willing too.

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#2 dan kessler

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Posted 17 February 2012 - 04:08 PM

Well, I guess you didn't like the answer I gave you before,
but I'm not sure you understand what a beam splitter is, either.

Beam splitters are nothing more than partial reflectors.
They "split" a light beam by transmitting part of it while
reflecting the rest of it.

They do not include lenses. They can be positioned behind
or between lenses, as they are in film and video cameras,
for various purposes.

Whatever it is you are trying to build, the beamsplitter will
be either a prism, a plate or a pellicle. There may be more than
one beamsplitter in the optical path, but any other components,
lenses or otherwise, are not really part of the beamsplitter.

You need to describe your project in more depth to get any
better answers, I think.
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#3 Brian Alan

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Posted 18 February 2012 - 05:09 PM

I didn't see an answer I thought I had made a post but I couldn't find it for some reason.

Anyway, I know it doesn't "include" a lens. I meant that I would like to make or purchase a splitter so that I could capture two of the same image with one lens. One lens with the image directed too two sensors. So I could say have one PL mount then a splitter behind it sending the light to two GH2's.

I know that there are in front of the lens splitters (like the ones in current use for 3D) and then there are the prism style splitters "behind the lens" style, again I know it's not an actual part of the lens.

I was thinking a three way tube style system. Pretty much a system that would allow you to have the male ends of the GH2 fittings so they twist on, then a female PL fitting. Then a rail system to hold everything in place.

Crude drawing...This is what I mean.

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#4 Brian Alan

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Posted 18 February 2012 - 05:21 PM

Thanks for the link too Anchor Optics, they have what it looks like I would need (cube splitters from 35mm-50mm).
finding the tube is going to be the trick or maybe I could just make it out a sheet metal box.

Sorry for the double post if a mod could delete the other one in camera accessories that would be great.
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#5 Chris Millar

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Posted 18 February 2012 - 07:55 PM

Your drawing is wrong ...

Although there is a lot more info available - you may as well read up more and research from the place you'll likely buy stuff from:


http://www.edmundoptics.com/
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#6 dan kessler

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Posted 18 February 2012 - 08:30 PM

As Chris indicated, your drawing needs to be changed.
The camera that is presently on the left will be
moved below the prism along the same axis as the
lens. The camera on the right will stay as is.

One of many other issues to consider is the back focal
length, or flange focal distance. With a PL mount,
you are using lenses that are designed to focus
an image 52mm behind the front surface of the lens port.
You must carefully compute the total distance through
the prism to the image sensors. That one problem alone
could scuttle your design.

If you want the image position to be exactly the same for both
cameras, then you must provide the means to align the rig with
pixel precision, then lock up ROCK SOLID. Nothing can move.
The tiniest wiggle will ruin it.

Are you good with machine tools?

Edited by dan kessler, 18 February 2012 - 08:34 PM.

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#7 dan kessler

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Posted 18 February 2012 - 08:52 PM

Of course, all of this begs the question, what will a rig like this give you
that you can't get with a single camera and After Effects?
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#8 Brian Alan

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Posted 18 February 2012 - 10:29 PM

Not everything in the world is about after effects. :)

An organization out of the UK came up with a new software thats kind of the equivalent too long exposure photos for film.

I would rather not give away the use for it as I think it would be wise to keep it with my self. I need one camera capturing the normal footage and one inputting into this program at the same time. It's not a filter, it needs to be done with recorded image at the same time you acquire the footage. Thus I need to use a beam split setup. I will ALSO be using after effects and rotoscoping too remove areas that I don't want the effect applied too, but I can't do it if I don't have two versions of the footage. :)

I have a friend thats is good with machine/tooling work who would assist in the construction.
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#9 Chris Millar

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Posted 19 February 2012 - 04:49 AM

Dan refers to the clearance issue I mentioned in your tilt/shift thread ...

You really need to think about that.

Hmmm let me guess, are you playing around with 360+ shutter angles ?

180 + 180 = 360 with one camera out of phase with other by 1/(2*fps)

Once you have those if you shoot fast enough footage you can effectively dial in your frame rate and shutter angle after the fact ;)

Have fun !
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#10 Brian Alan

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Posted 19 February 2012 - 06:25 PM

Dan refers to the clearance issue I mentioned in your tilt/shift thread ...

You really need to think about that.

Hmmm let me guess, are you playing around with 360+ shutter angles ?

180 + 180 = 360 with one camera out of phase with other by 1/(2*fps)

Once you have those if you shoot fast enough footage you can effectively dial in your frame rate and shutter angle after the fact ;)

Have fun !


I will check that out as well and start learning, but actually thats not what I was going to do. I want the girl dancing with the light and the light staying frozen in the air, because I'm using a strobing led
there will be individual dots in the air, then I can go in and slowly take them out one by one, thus having a moving light pattern in the air. There are some examples with junk cameras they used in these
videos. It can work with HD and non of these videos did anything with lighting or camera setup to get different looks. I sent you a PM chris with a link.
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