EOS 5D Mark III and programatic access to the internal light meter...

I am putting the finishing touches on my time-lapse robot. At the moment I'm using an external Yacto light meter to monitor and control several programming vectors, but I would much prefer to use the camera's internal meter, for the simple reason that it's "through the lens". Unfortunately, after combing through the SDK documents, I cannot find any way to access the meter's information outside the camera (i.e., USB). Before I give up entirely, I thought I would check with the forum. Anyone? Can the 5D Mark III light meter info be extracted via the USB interface? Thanks in advance.

The only thing I know is that it's technically possible, since Canon does it with their own software.
But I don't know how.

If the camera is equipped with Ethernet, you can set up a web server, where you can read out such data. But I guess you don't have Ethernet on that camera.

Thanks for taking the time to respond.

If Canon can do it in their own software, then I believe they are using undocumented features of the published SDK. The nuts and bolts of the physical interface (USB, firewire, ethernet, GPIB, whatever) shouldn't make any difference.

The closest I can find is kEdsPropID_WhiteBalanc​e, but unfortunately Canon has already superimposed a "meaning" on the data which is returned (Daylight, Cloudy, Tungsten, Fluorescent, Flash, Blah, Blah ) A discreet interpretation is useless to me.

I need access the the raw light meter data as a floating point value (lux), which is what I'm getting and utilizing already from my external Yacto light meter. If I could get this data out of the camera then the internal light meter could function as a drop-in replacement for the external one. Wishful thinking...

I doubt if you would get anything approaching a lux value from the internal meter, which lets face it, is never giving just a single output value. Regardless of the metering mode, the output of the cameras metering system is a whole set of values from each of the meter cells. These are then programmatically combined to match the metering mode. I would expect that even Canon's own remote control software is simply repeating the +- stops information that you see in the viewfinder when shooting in Manual exposure mode.

I'm very impressed with the system you have built there, I'm guessing that as well as setting camera functions and taking shots, you can also move it in multiple dimensions, as well as control the focal length of zooms, and quite a bit on top.

Alan

Can't you get the values for ISO, aperture and exposure time the camera has measured? From that you can calculate the brightness the camera has measured.