I understand that zoom lenses for still photography are not designed for movies. I also understand that primes are wonderful.
But for documentary work, zooms are imho essential.
With so many of us using DSLRs for video, I wonder whether there are any zoom lenses for Canon (Canon brand or other) which are parfocal, i.e., you can focus at telephoto, zoom out, and have confidence that the focus is still good at wide angle.
I doubt that any DSLR lenses are truly parfocal. But do any of them, in your experience, come close enough for all practical purposes? Even with focus assist devices like the Zacuto magnifier, or an external monitor, there are times when it is extremely difficult to ascertain critical focus at wide angles.