I will try other solutions as I am able, but I did successfully complete the session with my MKIII. Here is how the video was accomplished.
I used the TV Shutter Priority Setting. In video mode this allows me to specify the shutter speed. Apparently one of the most important settings for video. I set the shutter speed at 1/30, the most important setting for 30 frames per second video. The aperture & film speed then changed automatically based upon conditions.
Recording started just as the sun came up (lightness, but shadow). The subject was stationary, and focused about 4' from the lens, with landscape background. 28-70, 2.8 Canon L lens at about 50. Camera on a tripod with the sun coming up from the right behind trees. Recording lasted about 30 minutes.
Other than the color hue changes associated with sun rising, the video brightness remained near perfect. Motion occurred at the subject, off and on during this time but the finished video maintained focus. Other than some post production corrections to help normalize lighting, it went very well.
I did not notice any issues involving the depth of field during the video, in and about the immediate area of the subject. But in all fairness, I was in a field were the main subject was at the 4' mark, with just grass/ground until reaching trees and hills about 60 yards away. So I did not have the chance to observe just how much the DOF changed over time.
Thanks to all who helped!
PS: I don to think manual would have worked because the lighting changed constantly during the 30 minutes.
