constantly keeping the cameras in phase thru an external box that regulates the two cameras so they're always firing at the same time and that they don't eventually drift apart. My cable will just be a start/stop sync but from what I've been reading and as is the case with GoPro, start/stop sync should work well enough.
Just wondering, has anyone had any problems with sync with the GoPro since this will be the same concept?
Tom- first off- Genlock does not require an "external box." However in a studio environment, we do use a time base to send 'House sync" to all devices, cameras, switchers, character generators etc. In the field, the genlock process is quite a bit simpler- One camera is assigned as the Master clock. All other cameras, are assigned as slaves. Then all cameras are set for free run time code, drop frame. This is very important. Next, a short cable is connected between the master and each slave camera one at a time and the slave locked onto the master in a few seconds, then the cable is disconnected and the next slave is locked. There is no need to keep a cable connected as the clocks in these cameras are phase locked accurate for as long as a couple days, even when powered off because a lithium battery keeps the clocks locked.
The start, stop, and zoom control of the 3D sync controllers do not genlock as I stated before, but they do a pretty good job of starting and stopping to the frame. Some devices have a digital error readout where you can see how far out the frame sync is. These devices also have a zoom control that allows you to zoom the lenses simultaneously. Mine does a near perfect job of zooming with matched focal length. There is a myth that these cameras, go "out of sync" on long clip runs. I can tell you that none of my cameras with or without the sync box lose even one frame from beginning to end and the longest clips I have recorded were for an hour. I use a sound click in the beginning to match up the two clips and also make the same sound near the end. I have also tested with a stobe light flash. Never has one clip drifted over long running clips. I have tested The TD10, my NEX5n and the GoPro Hero 4 silvers. I consider this drift a myth and am so confident it is a myth, I sometimes forget to do the ending sound sync as a check.
According to query to tech support by Barry, I recall, GoPro confirmed the cameras actually are genlocked in the 3+ Black 3D system. The earlier Hero 3D version 2 was only a start stop sync mechanism. My own tests, confirm that the Hero 3+ Black sync/genlock cable does not phase lock the color so I prefer to use manual WB and raw settings. If using auto white, there is a possibility of a color mismatch between the GoPro cameras. If you manual white, then any color correction you apply to one will also work equally well to the other in post. Using auto tracking WB can be a nightmare to correct in post.
Exposure ( electronic (( E.V. and ISO) and iris) is much easier to correct as the parameters are so much simpler than color. Here you just have to adjust the brightness for proper black and peak white and done. But, I found that auto exposure with the GoPros and my other cameras is better left to auto than manual. Most of the time a lag in exposure change will never be noticed as the video plays. Set the shutter speed of your cameras to manual and match them in settings too.
Bottom line is 3D without genlock is good enough with minimal motion on static scenery shots. Scenes with lots of movement, people walking, water falls, and fountains, any movement at all, and the 3D becomes soft looking until the motion stops and then sharpens. Motion in the scene, genlock is a must.