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 ..
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