Camera Synchronization

Question

I'm interested in having two or more cameras precisely synchronized for machine vision purposes. All the global shutter cameras I've seen basically have two modes: free-running, with a maximum frame rate of X FPS, and triggered, with a maximum triggering rate of X/2 FPS.

This is a frustrating limitation. Shouldn't it be possible keep two free running cameras very closely synchronized using an external feedback controller? Each camera could pulse a pin letting you know when it's capturing a frame, and as long as there was a scheme for introducing a very slight delay into one or the other of them, you could nudge them together, similar to how the NTP daemon nudges a computer's clock.

Does anything like this exist? Is there a camera sensor or module out there which has the necessary rate control capability necessary for it?

Thanks for any thoughts or input.

Answer 1

One way to keep two cameras precisely synchronized is to send a genlock signal to both cameras.

"another application for which genlock is used is to ensure both sensors on two-camera 3D rigs fire at the same time." -- Timothy McDougal

Unfortunately, many good cameras do not have a genlock input.

Answer 2

I think unless you also synchronize exposure times (= exposures will be same for both sensors) then genlocking (feeding a common clock to the camera modules) is not a solution since after different exposure times the sensors will drift immediately from each other by the difference of exposure... Syncing exposures may be a bit tricky.

The other option is to use a sensor with HW exposure/trigger pin. Unfortunately there are not many affordable camera modules with such pin, the cheapest I found are mt9v032/mt9v034 modules on AliExpress - they are around $60.