This question is much easier to answer than what you can expect: get the 35L!

While both lenses have excellent image quality (the 35L being a bit better), the 24mm field of view (73′) is too large for most video scenes. While it works for stills, when things start to move the bigger than real life field of view creates some weirdness as things are getting closer to the camera (or frame edges).

On the other hand the 35mm feels closer to the perception of the human eye and will make your clip look natural.

I have shot with both and while I loved the feeling one can get from a wide panorama with shallow depth of field, it is too wide for general use.

Note 1: these comments are based on a full frame camera. On a cropped sensor, the 24L is preferable since the field of view becomes the equivalent of a 38mm.

Note 2: I am not saying the 24L is not a good lens. It has its uses, but given the choice between the 2 for video, the 35L will get more used.

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planetMitch

chief astronomer at planet5D LLC
Mitch "planetMitch" Aunger is the creator and mastermind behind planet5D.com — which covers every aspect of HDSLR cameras (and a whole lot of other cameras as well). A lover of photography since his early days, he graduated to selling stock photos to make a little bit of spare cash. It wasn’t much, but it allowed him to upgrade to better cameras as well as computers, and it wasn’t taking money away from feeding his family.
He loves the stories that the still image can tell. In the summer of 2008, he read a story written by Arnold Kim called “I Quit My Job” — Arn is the owner of macrumors.com. He started macrumors in 2000 as a hobby, and by 2008 he was making more money with the site than he was on his day job, so he quit. The surprise to the story is that he was a doctor making more than six figures! Right then and there, planetMitch dreamed about doing the same thing.
September 2008 rolled around, and Canon announced this new version of the incredible 5D — the Canon EOS 5D Mark II. It was the first Canon DSLR to shoot full HD video and the earth moved! (It really was a huge deal in the photography world.) planetMitch knew if there was ever a chance to ride a wave of something he was really passionate about, this was it — and the blog at planet5D.com was born. It is now one of the most popular HDSLR blogs on the planet, and he is making a full-time living from blogging. He couldn’t be happier!
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