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Old February 23rd, 2010, 02:08 PM   #1
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Beam-Splitter Rig

Is there an instruction manual or tutorial anywhere on the web for the design of a beam-splitter rig and what the best glasses (or mirrors) are that can be used?

I understand the challenge is in getting to allow all kinds of movements of each part to fine-tune the final 3D image. But let's say the rig is only designed for less than 20-30 feet, won't one fine-tuning at the beginning of the shooting day serve for the entire day? Can't calibrations be made that are then 'fixed or locked' somehow?
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Old February 23rd, 2010, 04:18 PM   #2
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there is company selling all kind of mirrors for prompter and they are cheap.
Teleprompter - Prompter products, beamsplitter glass, free software
the mirror rig is mode for 2 puposes.
1) it allows to put lenses (and camera body) close enough to reach a resonable interocular distance (about 2.7 inch or 70mm)
2) it is supposed to include many screws/rails systems to allows the best setting for cameras convergence.

the 2nd feature is hardly one you can achieve without real feedback (i mean something you can check with your eyes), so 3D monitoring seems something mandatory.
By chance is easy to do and for relatively low price.
If your camera are genlocked, a simple field mixer can take one field from a camera and another field from the other camera, mix them to recreate a regular video signal.
from the sync clock extracted from the video, you can drive a LCD shutter glasses.
the total cost should stay way below $1000 for SD monitoring, including a 10" lcd screen.
if your cameras are not genlocked, you need to add a frame synchronizer (about $700).
I believe this is really a corner you should not cut in your setup.

I used a NuView adapter years ago. The nuview adapter was in fact a mirror rig into a lens, so only one camera was needed. The good thing was you could check on the camera's LCD for the correct convergence and correct it with a screw on the newview.
Believe me, it was the most important setting of all the setp and needed to be touched every time i press the rec button.
So i hardly believe you can setup your mirror rig and forget about it.
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Old February 25th, 2010, 12:31 AM   #3
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What's a frame synchronizer? How does it work on cameras that don't have genlock? E.g., the canon 7d shoots in h.264, which is a compressed QT movie, will the frames still be synchronized?

The teleprompter mirror has a stereo display video but no info on how to build a beam-splitter rig. Even a basic design would do, because I'm sure there's a lot of tweaking needed.
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Old February 25th, 2010, 07:38 AM   #4
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all frame synchronizers are working the same.
they put the picture into memory and start to read the memory when ready.
The simplest and easiest is to use only on memory on one input as a delay line.
more sophisticated system will put both inputs into memory.
the result is you get one video synchronized to the other, or both video synchronized to a new clock signal that is neither from input A or B. the second solution is more robust, since you can loose an input without disturbing the output.

for the mirror rig, there are several way to do it.
you can use mirror to build a kind of periscop, that setup is used in military equipement to get an enhanced stereoscopic view.
http://www.theon.com/images/Dual-Mount01_large.gif
that is easy to build, you just need surface mirror and there si no particular problem with this solution.
see The Loreo 3d attachment.
this mirror setup can be used in reverse, but the drawback of reversing it is the need for big mirrors. camera will be positioned in a way that each camera is shooting right in the lens of the other one. you just need to put 2 surface mirrors at 45 degrees (plus/minus for convergence) that is a very easy setup.
The other setup (P+S technik kind) is more difficult because it uses semi transparent mirror.
It is the telepromter kind. Imagine a teleprompter. The camera is behind a semitranparent mirror (at 45 degree), so it sees the scene directly.
the other camera is located were would be the prompter screen (shooting up) so it sees the same picture, but reflected into the mirror. This way you can align lenses so they justshare the same picture, or misalign them to get the sterescopic effect.
there are several problems with that setup. You loose 50% of light on both camera.
One camera sees a mirrored image. You can correct that by adding a surface mirror to flip the image again. not to say that such setup is HUGE and heavy, and requires lots of time to install and align cameras.
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Old February 26th, 2010, 03:02 AM   #5
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that's a fantastic army gun - and it looks more compact than a beam-splitter. :)

Do you have any examples of frame synchronizers that can be used with DSLRs like the Canon 7D or 2Ti? Do we need a separate recorder and equipment on the field to make this happen?
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Old February 26th, 2010, 06:19 AM   #6
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if you use a frame synchronizer just to monitor, an SD model on composite signal should be ok. Do not forget that frame synchronizer are just synchronizing frames, not picture.
So if your left camera takes a picture slightly behind the right camera, synchronizing frame will just make frame arriving at same time to monitor, but the difference in both picture will stay. for synchronising the shots, you need to genlock cameras.
synchronizing frame is just useful if you need to mix both video signal to make a stereoscopic monitoring.
if you need to synchronize frame in HD, with digital format (like HDMI), you probably better go with a computer, because such device if exist, usually cost the hell.
HD synchronizer are usually using HD-SDI.
once you got signals synchronized you can use them in many ways to make a light and cheap "in the field" 3d monitoring.
I already gave the link to Colorado-video, a company that make very intersting video device at low price. Colorado Video - Creating Unique Video Instrumentation and Video Equipment since 1965
particularly look for model 614 .
then you need to multiplex (alternate one frame from left with one frame from right).
You can easily find electronic layout to do that, it is simply switching signals at the right moment. colorado video has model 315 that deliver all signals needed, but it is a bit expensive and incomplete.
The wireless shutter glasses and IR emitter can be found for $90 on Amazon
http://www.amazon.com/I-O-Display-Virtual-FX-Converter/dp/B00026SZBI/ref=sr_1_6?ie=UTF8&s=electronics&qid=1267186238&sr=1-6
with that you can take any pair of camera with composite output, any video LCD screen
and get 3d monitoring for 2 people.
You can even record the signal into a DV recorder and play it back later in 3D.
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Old February 26th, 2010, 12:34 PM   #7
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I think you need to be careful with teleprompter mirrors as I believe they are 60/40 and you need 50/50 for 3D otherwise your exposures will be pretty far off. Also, the quality of the mirror is of utmost importance as you can get drastic color variations on the lenses looking through it. Teleprompters do not require high quality mirror, just mirroring for text and for a single lens to shoot through unobstructed. All in all, my experience with teleprompter equipment over the years would steer me away from it and not towards it as a 3D solution.
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Old February 26th, 2010, 02:11 PM   #8
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Actually, that teleprompter site has a link to stereoscopicmirrors.com, which sells 50% mirrors. Though they are designed to make a 3D display.
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Old February 26th, 2010, 03:38 PM   #9
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if you got genlocked or frame synchronized camera, you can build this nice little circuit
Two Camera Field Sequential 3D Circuit Design

unfortunately, most of LCD screen do not work with interlaced frames (they are displayed at same time in a deinterlaced mode), so you have to make frame sequential instead field sequential. For that you switch glasses at each new frame, not new field.
Fort this you just use frequency divider on the field clock signal.
the drawback is this will flicker a lot more, but for short checking a shot, that is ok.
you can also use no glasses with such design and use the ghosted picture as is.
or you can try to find a LCD monitor that support interlacing (it exists, particularly for HD display).
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Old February 26th, 2010, 11:28 PM   #10
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Quote:
Originally Posted by Bruce Schultz View Post
I think you need to be careful with teleprompter mirrors as I believe they are 60/40 and you need 50/50 for 3D otherwise your exposures will be pretty far off. Also, the quality of the mirror is of utmost importance as you can get drastic color variations on the lenses looking through it. Teleprompters do not require high quality mirror, just mirroring for text and for a single lens to shoot through unobstructed. All in all, my experience with teleprompter equipment over the years would steer me away from it and not towards it as a 3D solution.
The same webpage has teleprompter mirrors at 50/50, just 50% more expensive.

But other than teleprompter mirrors, are there any other kind of mirrors that might work just as well or better for a beam-splitter rig?
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Old February 26th, 2010, 11:33 PM   #11
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Quote:
Originally Posted by Giroud Francois View Post
if you got genlocked or frame synchronized camera, you can build this nice little circuit
Two Camera Field Sequential 3D Circuit Design

unfortunately, most of LCD screen do not work with interlaced frames (they are displayed at same time in a deinterlaced mode), so you have to make frame sequential instead field sequential. For that you switch glasses at each new frame, not new field.
Fort this you just use frequency divider on the field clock signal.
the drawback is this will flicker a lot more, but for short checking a shot, that is ok.
you can also use no glasses with such design and use the ghosted picture as is.
or you can try to find a LCD monitor that support interlacing (it exists, particularly for HD display).
Do I absolutely need to mix video in this way to watch 3D on the set? If I have a computer/laptop, can't I run two signals and then use software to determine metrics (like a 3D calculator)? I also have the option to view the 'mixed' video in a number of standards. The output from the laptop goes to a 3d HD monitor/LCD that I can view using 3D glasses, along with the DP, etc. Am I missing anything?
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