The Term to Look up on your Search Engine would be "Mirror Rig"; "Stereo Rig" or "3D Rig".
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There are a bunch of people who used Mirror Rigs for 2 Cameras to double the Framerate (will put some References and links to pages with images throughout the Post here, mixed with some Comments from me between them, there is Plenty more out there, just meant as a little Help to get you started), here is about the simplest DIY Setup i know of, which actually works:
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https://www.youtube.com/watch?v=lItG7LdKO5A .
They used two Gopros here, and Rigged them up with some 3D-Printed Case and a Half Mirror, Alternating Trigger Timing was done by just randomly pressing Record on both and hoping timing would Line up well enough for that to work (quite a bit easier with the Chronos and most other Cinema Cameras, as they usually allow for some kind of external Timing Reference or External Trigger source).
While That Rig isnt ideal in some Ways, its a nice Proof of Concept.
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However, for use with anything bigger than an Gopro/ Phone/ Small Compact Camera, you will Quickly end up needing a more Serious Camera Rig, especially if you still want to have the Flexibility to Change Lenses, Point of Focus, ect. (Maybe even WHILE Shooting/ Focus Pulls/ Zooms). This Usually means that you need a rig that allows for a bunch of different Adjustments for Camera Alignment. Those Mirror Rigs are usually used for Professional 3D-Filmmaking. They are used to Allow shooting two different angles of the Same Image, closer together than the Size of those Cameras there usually allow for, Simulating the Distance of Human Eyes for more Immersive Movies. As the Distance of those two perspectives usually needs to be readjusted depending on what you are shooting (The Distance of the Two Cameras Perspectives is what sets the Viewers scale of Perception for the Scene (sorry i am not a native speaker, dont know how to say that better, hope its understandable enough...), meaning the Cameras will need to be closer together for Macro shots to not make the final image "fall apart" and needs to be further apart for Bigger Scale Shots to give enough of a difference in Perspective between both Cameras to still give an 3D-Effect at all.), those Rigs have all the Same Adjustments, which would also be needed for your use plus allow for Perspective Offset also. Only difference between 3D-Shooting and using a Mirror Rig for Frame-Rate Doubling is the Camera Offset and timing of Frames across The Two cameras (3D Footage will be shooting both frames at the exact same Time).
Here are some Examples of Professional 3D-Rigs:
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http://cinemavision.com/mr https://hd-cinema.com/Genus-Hurricane-3D-Mirror-Rig.html https://urbanfoxtv.blogspot.com/2011/05/decode-to-launch-new-3d-mirror-rigs.html?m=0 https://www.live-production.tv/case-studies/sports/sixteen-3d-rig-manufacturers-overview.html http://3droundabout.com/2011/11/5446/how-to-calibrate-3d-mirror-rigs.html https://www.fxguide.com/fxfeatured/reach-for-the-sky-mpc-goes-full-circle/ https://markhardin.com/naturalvision/ .
Now, as Rainer allready said, as soon as you start doing this With Higspeed-Cameras, you will need
a Lot of Light...
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http://shootdatapost.com/blog/2011/6/30/3d-flex-tease.html .
Also, depending on your Lenses, Weight and Size of the Rig itself and whatever other stuff you also put around your Camera, the Whole Rig can get pretty big and Heavy rather Quick. Now the Chronos Cameras are somewhat small and Light Cameras compared to most of the Full-On Cine Cameras shown in the Links above, but depending on your lens, you will still be very likely to end up with an Rig which exceeds the Weight Limit of most Entry-Level Video Heads, which would be more than apropriate for a Single Chronos. Things get even Worse for any Shots which need the Camera to Move in any way, like A Dolly, Gimbal or Crane. In summary, if you end up doing that, make sure you have a camera Support, which can Handle size and Weight of the Final Rig if you dont want to end up breaking Your Tripod and / or Cameras: .
https://qph.fs.quoracdn.net/main-qimg-7d4aca5f09200d741a463cbe9fa17908 (This Image is quite absurd of course, but just to make a point here about Camera Supports which are apropriate for the Size and Weight of Rig used, this is a Vinten MK7, able to handle like 100kg and also the Size of such a Camera...)
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So, now as A
Summary of the Whole Topic so far, is this worth to do?
A few years ago, i came across some very well Article on a Website (which was allready old then), where someone also rigged up two Phantom Miro (or older Flex) Cameras for Higspeed-3D Shooting, where they in depth explained Pros and Cons of Mirror Rigs, but i can sadly not find the Article anymore, seems to be lost..
Somewhere in there they wrote something like:
"While this Half Mirror now solves the Camera Offset (they bevorehand explained why it was very important to get the Offset Right to make the 3D-Footage Feel Right, and why its difficult to do because of the physical Camera size), it introduces a ton of other Problems (going on with explaining them in detail)".
Which in my opinion is a very good summary of the Whole thing about Mirror Rigs.
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I personally must say, i havent used any actual Mirror Rigs (with 2 Cameras) in Production ever, apart from Prompters, but even the Prompters with Small Cameras got uncomftably bulky and heavy very Quickly.
I thought about building one for some time however, to make some cheap fast Camera, but ended up realizing that it is just too much work and not really practical for the Result it gives.
In my opinion now, just not worth all the work, because in order to get at least half decent Results from such a rig, you need to allready do it somewhat propperly (ofc. you can fix a little bit in post with aligning the Footage there, and croping a bit, but thats kind of against the point of doing all that in the first Place...then you could just have shot in lower Resolution and Higher Framerate to beginn with...), and as a Result "only" double your Framerate.
Given that you also end up needing TWO entire Cameras, Lenses and whatever else you have attached to them, its worth considering just getting an more Powerfull Camera at that point. Now for 3D its a bit different, as you need the Physical offset to get the Image Effect you want, so there is now way around such a 2-Camera-rig, and bigger, Heavier Cameras here usually means just better image Quality, but for Frame Rate doubling, you can usualy get better single Cameras somewhere, when it comes to Highspeed-Cameras.
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Then there is also Simulated "Fake" Slow Motion by Software which basically generates Frames in between the Frames Your Camera Shot, to slow it down more and still have it look smooth. Used The Twixtor Plugin for Adobe AE and got Useable Results with up to 25% Playback Speed (meaning for every 1 original Frame from Camera the Software generates 3 New frames, making 4 final Frames, so every 4th frame is a real one, the Rest are filled in by software with generated images), and good results with 50% Playback speed.
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https://forum.krontech.ca/index.php?topic=415.0 .
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There is also the other Take at the Whole Topic of multi-Camera Setups /Optical Arrays of just putting them Next to each other in some way or another, and not using Mirrors at all.
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https://area.autodesk.com/life-in-3d/technolust/?src=vr https://www.photofacts.nl/fotografie/rubriek/wetenschap/telescoop-van-10-canon-400mm-objectieven.asp http://graphics.stanford.edu/papers/st_interp/ https://www.roadtovr.com/lytro-immerge-latest-light-field-camera-shows-major-gains-in-capture-quality/ http://graphics.stanford.edu/projects/lightfield/ https://graphics.stanford.edu/projects/array/ http://graphics.stanford.edu/papers/CameraArray/CameraArray.mp4 (Keep in mind this is pretty old, was quite Crazy technology back then)
https://www.krontech.ca/chronos-ring/ https://www.newworlddesigns.co.uk/production-bullet-time-rigs/ https://petapixel.com/2012/12/24/freezing-time-and-space-using-a-bullet-time-rig-of-100-digital-cameras/ https://www.popphoto.com/news/2014/07/bullet-time-rig-uses-50-canon-1d-x-dslrs-and-24-70mm-f28l-ii-lenses/ https://www.rocketstock.com/blog/cinematography-inspiration-explosive-bullet-time-action/ .
Now, while you can certainly build Mirror Rigs with 3 or even more Cameras or Image Sensors if you really wanted to (an example would be an Old DLP-Projector, or 3CCD Camera, which both use 3 Seperate Optical Paths for Capturing or Projecting Images.), the Mirror Optics and overall Rig For that gets ridiculously complex. So an easy way to Stack even more Cameras than 2 Together is to loose the Mirrors all together and just mount them somewhere, pointing in the Same Direction. Problem you now have is, that your Perspective will constantly be shifting around. In some Cases, this might be the Desired effect, like Bullet time Rigs, where the Camera just "moves" so fast, that it is impossible to move a physical Camera at that speed, and instead you just use a seperate Camera for each single frame (can again be filled in with generated frames from Fake-Slow-Motion Software to smooth out the Motion and cut camera cost in Half or Third). But in case thats not what you want, you end up with footage that is constantly "Vibrating" around. If you can get far enough away from whatever you are shooting however, the difference in Perspective CAN be so small, that it wont be too noticeable usually.
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As A Conclusion, my current personal opinion is, that if you allready happen to own two identical Cameras and Identical Lenses (also lenses need to be identical!), and maybe even have acces to an propper Mirror Rig or can easily build one with some DIY, it might be worth a Try, but expect to put quite a bit of time and effort into it, until you get perfect footage. Otherwise i think its not really worth it, unless done on a really large Scale or to go beyond some Technical Limitations of the Best Cameras out there, as shown in some of the Links above. There is a Reason, why there is so few examples of 2-Camera Setups like this....
So i personally wouldnt go and buy a Second Camera and Lens(es) just for doing that.
I would try to get along with using Simulated (Fake-Slow-Motion), just higher Framerate Settings on the Camera itself, or actually looking into getting an Camera Upgrade (remember, you can also Rent really High-End Cameras if you really NEED them just for a short bit).
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As Also allready Mentioned in the Beginnig, there is way more info about this to be found, this was just meant as a quick overview of most of the stuff i know about the Topic in general and my point of view on this.
