Author Topic: Using Two Cameras to Capture 2x the Frame Rate  (Read 1745 times)

lwaters

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Using Two Cameras to Capture 2x the Frame Rate
« on: March 09, 2021, 05:04:49 AM »
Hi,
  Has anyone tried using two Chronos cameras to capture alternating frame to therefore double the frame rate?
Thank you,
Laura

MarcinS

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #1 on: March 09, 2021, 11:21:29 PM »
« Last Edit: March 09, 2021, 11:30:52 PM by MarcinS »

Rainer

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #2 on: March 10, 2021, 12:11:53 AM »
Hi,
I once tried this with two other cameras which have an external trigger. I got a cheap beam splitter from Aliexpress which is a small piece of glas which reflects 50% of the light and lets 50% of the light pass through it. When you arrange the two cameras 90 to each other, one looking "through" the beam splitter and one looking on the reflective side, they both see the thing you want to image. (It's best to google some images for this, it's hard to describe with words)
Then I triggered the cameras alternatly and combined the two "picture stream" in an interleaved way afterwards to a movie.
In principle this worked, but it became evident, that you need more light and that the alignment of the cameras and the beam splitter is crucial. If they are slightly off, the image jumps frame by frame. If the offset is only small, one can try and correct this in the final images and "shift" one image stream in a way that the overlap better.
So it is possible (with Chronos or other triggered cameras) but it takes quite a lot of preparation.
Best regards
Rainer

Nikon1

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #3 on: March 10, 2021, 06:12:13 AM »
The Term to Look up on your Search Engine would be "Mirror Rig"; "Stereo Rig" or "3D Rig".
 .
 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:
 .
 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.
 .
 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:
 .
 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...
 .
 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...)
 .
 .
 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.
 .
 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.
 .
 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.
 .
 https://forum.krontech.ca/index.php?topic=415.0
 .
 .
 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.
 .
 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.
 .
 .
 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).
 .
 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.
« Last Edit: March 10, 2021, 06:34:21 AM by Nikon1 »

lwaters

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #4 on: March 11, 2021, 01:11:59 PM »
Wow, thank you for your responses!

Not really looking for a 3d view, just trying to maximize the amount of fps with two or four Chronos Cameras. How do you ensure their synchronization?

One of those articles, I could not believe the size of those lights on their little subject! I need those lights! Where on earth do you find ones so large! Wild.
I understand with beam splitting we will need a lot more light.

Thank you all!

Nikon1

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #5 on: March 11, 2021, 01:13:55 PM »
Wow, thank you for your responses!

Not really looking for a 3d view, just trying to maximize the amount of fps with two or four Chronos Cameras. How do you ensure their synchronization?
Feed them with an external Trigger. If you send the Same Trigger Signal to both cameras, they will trigger Syncronous. Use an Offset accordingly to the Number of cameras you use for your Trigger Signal to get Frames Taken at regular Time Intervals.
« Last Edit: March 11, 2021, 01:40:25 PM by Nikon1 »

Nikon1

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #6 on: March 11, 2021, 01:27:02 PM »

One of those articles, I could not believe the size of those lights on their little subject! I need those lights! Where on earth do you find ones so large! Wild.

Looks like at least one of them is some Lamp from Arri
 The user julien uses a pair of ARRI Daylight M18 Lights. I personally also own two older HMI Lamps (1200+600W), but they are not useable for anything above 25fps, cause they flicker, you need ones with a Special Inverter for Highspeed Filming. But those, especially these Arri ones are crazy expensive.
 .
 https://forum.krontech.ca/index.php?topic=613.msg4202#msg4202
 https://www.bhphotovideo.com/c/product/1490756-REG/arri_l0_0006575_m18_hmi_with_eb.html
 .
 Could also be Straight up tungsten Lamps, like 4kW to 10kW Lams or something, but that would be just a oven at that point and Starts to be a serious Fire Hazard. So because of how close they are with those Lamps, i hope those are Highspeed-Ready HMIs or something like that. Dont really know the exact Lamps they used there.
 
« Last Edit: March 11, 2021, 01:28:43 PM by Nikon1 »

Nikon1

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #7 on: March 11, 2021, 10:04:00 PM »

One of those articles, I could not believe the size of those lights on their little subject! I need those lights! Where on earth do you find ones so large! Wild.

Looks like at least one of them is some Lamp from Arri
 The user julien uses a pair of ARRI Daylight M18 Lights. I personally also own two older HMI Lamps (1200+600W), but they are not useable for anything above 25fps, cause they flicker, you need ones with a Special Inverter for Highspeed Filming. But those, especially these Arri ones are crazy expensive.
 .
 https://forum.krontech.ca/index.php?topic=613.msg4202#msg4202
 https://www.bhphotovideo.com/c/product/1490756-REG/arri_l0_0006575_m18_hmi_with_eb.html
 .
 Could also be Straight up tungsten Lamps, like 4kW to 10kW Lams or something, but that would be just a oven at that point and Starts to be a serious Fire Hazard. So because of how close they are with those Lamps, i hope those are Highspeed-Ready HMIs or something like that. Dont really know the exact Lamps they used there.

 Did Some More Research on those Lights in that Image, and seems like they are 10 or 12kW each. Here are some More References for those Lights:
 .
 http://www.coloradogriptrucks.com/portals/14/pics/041%20comp.jpg?ver=2017-04-18-112346-000
 http://www.coloradogriptrucks.com/Equipment-Available/Lighting
 https://www.bhphotovideo.com/c/product/273615-REG/Mole_Richardson_4371_10_12K_Molequartz_20_Tener.html
 https://sep.yimg.com/ay/filmandvideolighting/demo-arri-t12-12k-tungsten-fresnel-light-5.jpg
 https://www.arri.com/en/lighting/tungsten/studio-t/studio-t12
 https://www.bhphotovideo.com/c/product/149969-REG/Arri_533100_12_000W_Fresnel.html
 

lwaters

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #8 on: March 15, 2021, 05:10:01 AM »

Could you elaborate on triggering? What is a good triggering system that can ensure if we're shooting at 40k we are capturing alternating frames?

Nikon1

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #9 on: March 15, 2021, 05:19:04 AM »
While i know a fair bit of theory behind how this would work, i must say, i personally never actually did any external Trigger stuff on the Camera so far. So, for actuall know-How on an Setup to use, i would reccomend to contact or ask someone who has allready done that, and can tell you what to do and what to avoid. I know clkdiv here on the forum did some advanced External Trigger setups, so maybe he can help you out a bit with this (there are propably plenty other people, but he is the first one that comes to my mind with this stuff).
 .
 https://forum.krontech.ca/index.php?topic=597.0
 

Rainer

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Re: Using Two Cameras to Capture 2x the Frame Rate
« Reply #10 on: March 15, 2021, 08:26:34 AM »
For my tests with cameras and external triggers I tried a function generator and an Arduino.
tl;dr: it was easier with the Arduino

I have a two channel function generator (Rigol DG1032Z to be precise). I configured it in a way, that on channel 1 I get a 5V trigger with my desired framerate, e.g. 1000 Hz.
Then I configured channel 2 in the same way. Then I set channel 2 in a way, that the triggers from channel 2 are exactly inbetween the triggers from channel one.
(Google "phase difference" for more info) Some function generators specify this in degrees, so a 180 degree phase difference means that channel 1 is shifted half the frequency.
This did work. Out of my two channels came alternating triggers.
And now the "BUT":
When I wanted to change the frame rate, I had to configure the second channel again and completely new. I tried all settings (locking the channels to each other,...) and read the manual, but changing the frequency (which means framerate) always made the settings from the 2nd channel messed up. I configured the generator with the buttons on the device. You can also do this via an USB connection, but then I used an Arduino.

And there - within 5 minutes I had 2 pins alternating the triggers with ease. It is basically just some delays and pulling the pins up and down.
I did this "manually" by changing the delay times in the source code and it worked good enough for my basic tests. I wanted to test the beam splitter after all.
One could modify the Arduino sketch maybe even with a display to create a changeable frequency with a rotary enoder as an input. But this was too much effort since I had a running solution for my tests.

I hope I explained everything in an understandable way.
Tell us when you ever try it, lwaters, I'm interested in your solution.