camera to camera sync?

[Les Dittert]

Thanks Dave , moco mode looks usefull . So if I want to have the viewfinder show something, can I just keep sending it pulses while not recording, at say 30hz, to position things for stop motion, etc, and then pulse only when I need frames while under record mode ?
sounds like this could also facilitate advanced ramping varispeed shooting as well...
Thanks!

[Justin Pentecost]

I did some tests with the Epic in "Moco" mode as described by Dave .. The most important thing is to test test and test again as I could forsee an almighty balls up .. I wrote everything up on the vimeo site and you can see the videos there as well.

http://vimeo.com/41691829

My test was very instructive and I will do another one as soon as I have some time and Jeff Brown has a camera free he can lend me ..

Here is the origional text I wrote (It's on the vimeo site too ..)

According to the documentation the Red Epic can accept an external TTL pulse as a sync input. What happens is that when a the voltage on the “Sync in” pin of the 4 pin lemo “Sync” Socket rises past 3.3V then the camera takes a picture at the present frame rate.

The theory runs that if you set the camera to 25fps then the camera will take a picture with a 1/50th of a second exposure whenever a pulse is sent. According to the documentation this will work at up to half the framerate of the camera ie 60 FPS.

Now this would obviously be a great thing both for moco sync as speeds “Off” 25 (24) could then be used with full moco sync.

Jeff Brown was good enough to lend me a Red Epic, for the weekend and he also lent me the “breakout” cable with three BNC plugs on it.

I had built an external sync box with a Cinematography Electronics PSC. I built a circuit to sub divide down to a single pulse per frame lasting 1/16 of the frame. This output was driven through a Schmitt trigger and then put into a BNC (the Schmitt trigger was not really required but it means that the rig is guaranteed to run a number of TTL loads from the output).

The box also had a linear display showing the phase of the signal at any given moment with a big red light to show when the shutter is firing.

A second output is sent to the kuper rig as a sync pulse.

For the test I set up a “POM” type checker running at 1fps (running anticlockwise) next to a Stepper Motor with a know with a white arrow on it. I set a move in the kuper rig to run for 1000 frames and to do 1000 revolutions on the Stepper motor. So in theory the stepper motor would show a blured image for every exposure.

I set external sync box to 25fps and then ran the move I noticed at the time that I had not seen a bloop light (the set of four lights on the far left) in the image. But the image on the screen was what I had expected to see .. Ie:- the disk was showing a blur over 50% of it's area indicating a shutter angle of 180 degrees.

I did a second pass exactly the same to check that the moco sync was working .. which is plainly was .. as the blurred parts were the same.

I then ran the same setup twice at 12.5 fps (and again the sync was fine and on this one you can see both the bloop lights) and twice at 6.25 and twice at 1 fps. All this still with the camera set to 25fps so they would have 1/50th second exposures.

I then did the same setup with the camera being run directly from the camera axis of the Kuper rig at “25fps” and 12.5 and 1 fps ..

Then I did a Kuper “Party” speed ramp so ramping from 0.1fps to 25 and then back to 6.25 and on to 3 then back to 25.

The “morning after” I took the camera and the rig out into the field and shot a simple pan driven from the PSC and from Kuper and then a simple ramp

I also did try a pass with an “impossible” pan so a 90 degree pan in 5 frames ramping the framerate so that the pan actually could take three seconds to move.
When I finally rendered out to the footage to something viewable (I should have taken up Jeff Browns offer of the Red Rocket!) the first viewing made it plain that something was wrong. The “25 Fps” pass was only 500 frames and not 1000 and the in the footage in the field it was very obvious that the dogs were not running at 25fps.

What I think has happened is that I misunderstood the spec on this feature. I think what it means is that the camera will sync up to ½ of the shutter speed set on the camera. So if the camera is set to 25 fps then the maximum speed you can run to is 12.5 and at 120 it would be 60. The next question is, “Is it possible to set the camera to 50 fps and a 360 degree shutter so you can shoot 25 fps with a 1/50 second exposure ..”

I will be shooting some more tests soon to see if that theory is correct ..

[Les Dittert]

Thanks for the test info Justin!

So the Camera ignores the pulse if it's too soon ( 1/2 frame rate ). I agree that it would be nice to use a 359 degree shutter for certain looks.
Maybe Red can look into that code a bit.

But first that have to finish sensor reverse (upside-down) scan ;)

[Justin Pentecost]

Now you have me worried Les .. I had assumed (I'm not a red owner just a moco op) that the camera would do a 359degree shutter. My understanding (and I sort of hesitate to speculate as there are people here who actually know!) is that the camera treats the frame as both open and closed ... IE ..

Normal 25FPS 180 degree shutter (c is closed O is open)

ccccccOOOOOOccccccOOOOOOccccccOOOOOOccccccOOOOOOcc ccccOOOOOOccccccOOOOOO

What the Red camera sees as one frame

ccccccOOOOOO

So when impulsed at 25 fps

ccccccOOOOOO ccccccOOOOOO ccccccOOOOOO
p p p p p

So half the pulses ignored

If the camera is set to 50 fps but pulsed at 25fps then you get this ..

cccOOO cccOOO cccOOO cccOOO cccOOO

So you get 25 frames in a second but with a 100th second exposure (Ie a 90degree shutter)

So my idea was to set the camera to 50fps and a 360 degree shutter and then you get this ...

OOOOO OOOOO OOOOO OOOOO OOOOO

Which is the same as the normal 25fps sequence the 360 degree shutter would not be an effect .. just a way of opening up the exposure ..

However from the tone of your post I understand this is impossible ..

[Dave Winder]

Thanks Dave , moco mode looks usefull . So if I want to have the viewfinder show something, can I just keep sending it pulses while not recording, at say 30hz, to position things for stop motion, etc, and then pulse only when I need frames while under record mode ?
sounds like this could also facilitate advanced ramping varispeed shooting as well...
Thanks!

Yes, thats exactly what you would need to do. We're working on making it automatic, so you could have preview and then switch to pulses when you hit record, then back to preview when you stop.

[Dave Winder]

What I think has happened is that I misunderstood the spec on this feature. I think what it means is that the camera will sync up to ½ of the shutter speed set on the camera. So if the camera is set to 25 fps then the maximum speed you can run to is 12.5 and at 120 it would be 60. The next question is, “Is it possible to set the camera to 50 fps and a 360 degree shutter so you can shoot 25 fps with a 1/50 second exposure ..”

I will be shooting some more tests soon to see if that theory is correct ..

Yes, the limitation is that using the MoCo mode, the pulse rate is limited to half of the selected framerate. So if you are going to give pulses at up to 25 fps, set the camera framerate to 50. Shutter speed is set separately.

You can set the shutter at 360 degrees to get 1/50 with the framerate at 50 fps

The duration of the pulse has no meaning to the camera.

[Erich Ocean]

Dave, how can we Master/Slave more than one camera? I'm wanting to do a setup with anywhere from 3 to 7 Epics, and would like to be able to have one camera control start-stop on all of them.

[Dave Winder]

Erich, as long as you are only talking master slave of control (not timing) you use the GigE functionality. Connect all the cameras via RED GigE cables to an ethernet hub. Follow all the setup in the ops manual, and you will be able to have the slaves mirror the master. hit start on master and they all start recording.
Having said that, please contact your Bomb Squad rep about your particular hardware. There was a hardware update concerning the GigE port and compatibility with hubs at one point.

[Gerald Thompson]

Response to Justin Pentecosts tests.

I recently used an Epic for a motion control shoot where we needed to run multiple sync passes at 6 fps. Control system was kuper. I used an Isotech sync pulse generator to slave both the Epic camera and moco. The Isotech device outputs a standard TTL 5v square wave signal, which can be accurately set to any frequency.

Initially I attempted to use the flash sync output from Kuper to slave the Epic, however this method proved impractical because unless the moco move is running, no sync signal is being generated and the camera does not update the display. By using the external sync generator it can be running constantly.

"using the MoCo mode, the pulse rate is limited to half of the selected framerate. So if you are going to give pulses at up to 25 fps, set the camera framerate to 50. Shutter speed is set separately." (Dave Winder)

The main glitch I found was that setting the camera frame rate to 12fps (exactly double as advised) - I found that only half the frames were actually recorded. Only when I increased the camera frame rate to 13 fps did it work properly. This meant that by setting the max camera exposure time of 1/13th second - the max effective shutter angle was 166 degrees.

Another gotcha was that if the camera was shut down while still in moco sync mode - upon restarting, the camera would be locked up and the menu unresponsive, unless the sync signal was present at time of booting up.

Otherwise the results of the shoot were good - all passes synced perfectly.

I also tried to use the shutter sync output from the camera but this could not be detected by Kuper. I had no cro to check for the presence of the signal - it's possible it was present, but either the pulse duration is too short, or the voltage too low for kuper. At a later date I intend to investigate this further and build a 3.3v TTL to 5v converter if necessary.

In the long term, if the shutter output can be made to work, it would be better than using the sync system described above. Then the camera assistant could more easily remain in control of the camera fps and shutter angles, with more flexibility and less chance of locking up the camera.

Gerald Thompson

www.bfg-motion.com

[Dave Winder]

Gerald, what version code are you running? There was a point where lengthened the shutter out pulse from nano seconds to tens of microseconds, to make it easier to use on a scope. But even the very short version should trigger any edge circuit, unless the Kuper is filtering it for debounce or something. However, it is 3.3v. I dont know what the Kuper expects to see, but if it wants 5v, that could be your problem.
I will have to look into your 12 versus 13 fps issue. The reboot in MoCo mode is a documented issue. we are working on making that more user friendly.