Dual Camera rig

R

robin746

Member
I am looking for an inexpensive option for rigging up two small cameras (Panasonic GH1) so that the axis of the lenses are as congruent as possible. I am thinking that this means one camera on top of the other. (I'll flip the video from one unit in post.)

Currently I have a breadboard on order, plus an articulated arm. I am not sure that will do the trick to get a stable enough configuration.

I will be using adapted lenses with a larger image circle than the Micro Four Thirds sensor. Then I can use a tilt adapter to compensate for the lenses being physically separated and hence off-axis. Am I thinking this through correctly?
 
Have you considered a teleprompter setup? It's probably more than you want to spend, but it would get the cameras exactly on-axis. I've seen a DIY teleprompter that someone did for low dollars. I'll post a link if I find it.
 
The budget is pretty well nonexistent! That's why I'm starting with a very basic cheeseboard and arm. I thought a cage would be better but couldn't find one tall enough to mount two cameras inside one on top of the other. I am sure a cage designed for a significantly larger camera could fit two GH1 units, but then the cost (for a few pieces of machined metal) gets into the range of my total hardware budget.
 
I found a place that supplies just the half-mirror. You can get a piece of 6" x 6" mirror for $25. That along with some plywood, cardboard, and/or sheet metal, will do the job.

[h=1]Order Ohttp://www.telepromptermirror.com/fs.asp?product=Teleprompter+Mirror&customsize=yes&mirrortype=Glass+Teleprompter+Mirror&substrate=glass&height=6&width=6&unit=inches&quantity=1&transparency=40R%2F60T&thickness=5%2F32%26quot%3B+%284mm%29&Submit=Calculate+Pricenline[/h][TABLE="width: 400"]
[TR]
[TD="align: left"]Product: Glass Teleprompter Mirror
Transparency: 40R/60T
Thickness: 5/32" (4mm)
Height: 6 inches
Width: 6 inches
Unit Price: $25.00
Quantity: 1
Total Price: $25.00[/TD]
[/TR]
[/TABLE]
 
I am not getting my head around how a teleprompter mirror would help. I could buy two, install at 45 degrees and point the cameras at each other with the mirrors in between. But that would make it pretty hard to use the LCDs or viewfinders, which would then be exactly opposite each other.

Perhaps I am missing something.
 
It would depend on what exactly it is you want to achieve with the setup.
Is it for something like a stereoscopic idea for 3D in which case exact focal alignment is not critical or do you need exactly the identical image on the sensors of both cameras?
The ideas of the teleprompter and half mirrior would be for exact alignment, the one camera shooting through the mirror in the normal position and the other in front and below it shooting up into the reflection on the mirror thereby resulting in two identical focals.
Looking through both cameras wouldn't be an issue if the are identical and 'seeing' the same thing.
 
I was thinking the second camera is not below like a teleprompter, but upright in a normal position, but just 90 degrees from the other camera for ease of use.

There is the light loss of the split image to consider.
 
Maybe you could adapt the teleprompter.

I'm not being a smart-ass when I ask this but is there a particular reason you can't just duplicate the 'footage' from the one camera? Just curious.
 
The idea is to explore the interaction between the optics and the dance (which will be choreographed with this in mind, once we have a chance to rehearse and see what works and what doesn't).

Imagine that two identical cameras with two identical lenses are used from the same perspective. Set a wide aperture so that DOF is thin. Setting each for a different focal plane will then reveal different aspects of the movement depending on where the dancer's movements take her in terms of distance to the camera. You can't do this in post starting with a single reel, unless you impose some blur "effect".

This is just one possible scenario -- another might involve different lenses with different focal lengths, to enable superimposition or sequencing different FOV.

Why not shoot multiple takes? A well-rehearsed dancer replicating movements will appear to exactly repeat motion when viewed from a distance typical of an audience in a hall. But in fact there are many small differences in each run-through. A tightly-focused camera -- especially using a lens at f/1.2, for example -- would easily distinguish between these.

Besides, this being an art project we want to do something different. The idea is to make the optics an implicit part of the dance, so the resulting video is not mere "documentation" of something that could have occurred without filming.
 
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Well, sounds awesome. Very clever idea.
Sorry I can't offer an easier solution.

Best of luck with the project and I hope to see it sometime.
 
Thanks!

I do hope that once I get the components I will find that an articulated arm does the trick.

Another option is a C-bracket large enough that two cameras can be above each other. I haven't found a source for these yet, as the cheaper ones seem purpose-designed for Canon DSLRs. Bigger than a GH1 but too small for two of them!

If anyone has found a C-bracket the right size...
 
After some delay I am coming back to this problem. In the meantime I have obtained the cameras, lenses, supports, etc.

I think I finally understand that a simple mirror is not the solution, but a pellicle (AKA beam splitter) is. Sorry for my ignorance in how a teleprompter actually works!

With a beam splitter the same virtual image will end up in two places, and each camera goes exactly there. The light loss is not a big concern, since I will be shooting fast lenses anyway. Building the rig is more of an issue since I am not so practical!

Anyway, take this as a small update. I am now on the lookout for a beam splitter.
 
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My links provided you with the beam splitter for $25.00. The rest of it is pretty simple. Take a tripod and mount a piece of plywood big enough for 2 camera heads and the mirror. You need to keep the cameras as close as possible to the mirror to keep the mirror small. The farther away from the mirror the camera are, the bigger the mirror needs to be.

Just as with a teleprompter, the camera which has the image passing straight through the glass must have a black cloth (or similar light blocking) draped between the lens and the mirror for the beam splitting action to work.

As a very quick and dirty way to mount the mirror, just use some cardboard and glue to make supports for the mirror. You can get more sophisticated then that if you want. But to prototype it and see how it works, you can get it set up very quickly with hot glue and cardboard. Then, when you have it working the way you want, you can use better materials to make it more solid.
 
Oh yes, thanks for the link previously! I should have been more precise in saying I was on the lookout for a source here in Europe, since shipping is otherwise prohibitive ($95 from the site you referenced). People outside the USA generally have no reason to realise that international shipping rates have doubled twice in the past number of years. I no longer buy anything from N. America -- the prices are simply stupid. Whereas in Europe or Asia postage is quite reasonable.

(EDIT: That retailer has a $54 shipping option with USPS. Though exorbitant it might actually be my best solution!)

I would also like to source a 50/50 beamsplitter (not 70% or 60%) in order to ensure the same light at each camera.

Unfortunately I have not found a European source at this time.

As far as DIY goes, there are several projects on the web for a teleprompter, which I will provide here for the benefit of others reading. Teleprompter Mirror themselves have one. Griffin hammond has a useful video. And then Russell responded with an even cheaper build, something like the mock-up you were suggesting.

My own build skills are rather useless, since I am physically limited. I will need to have a rather precisely made rig, even for proof-of-concept, since registration of the two images is key. So I hope to tap into some local manufacturing talent.

A good start would be to find a black box with the correct diagonal measurement, that can have appropriate lens openings cut in two sides.
 
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I do wonder what the minimum size glass would be for lenses with 52mm front diameters.

Edmund Optics have a 75mm X 75mm X 1mm plate beamsplitter (50R/50T) for €66.50 + €20 shipping + VAT... which comes to €105 -- ouch! I am thinking that might be large enough if the lens was close to the glass.
 
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