Part 2:

Hardware problem, adressed by the manufacturer here:
If you experience it, chances are you might have a defect model. Contact your seller or BlackMagic directly in that case.
As for the video any realation between zooming in and a change of brightness can be excluded as I used a zoom lens with continuous 2.8. aperture. Besides, the phenomeneon can also be seen in the pan at the end. Sorry for bad operation, was just getting used to camera, lens, tripod. Hope this helps avoid bad surprises after long and expensive shoots. Used model was the EF version.

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