Canon EF lenses - aperture control
This is just a matter of curiosity on my part: If, as I believe, Canon EF lenses change aperture in 1/3-stop steps, how can they be considered for videography, where you sometimes have to change aperture during a shot?
Clearly I'm missing something, as you see even very sophisticated cameras with EF mounts.
That is largely correct, though you might be able to change which fractional increments you can adjust the lens with certain cameras, not sure. I don't really use Canon EF lenses with cine cameras.
That being said, many people are willing to compromise on this (and other) mechanical drawbacks due to the fact that you can get a very cinematic look from such lenses at a FAR lower cost than their cine lens equivalents. Many people also simply don't change the iris during a shot, or if they do, it's clearly intended to be a correction and meant to be edited around rather than discretely snuck into a shot and therefore this issue isn't really a big deal. I largely fall into this category, the type of work I do very rarely requires me to smoothly and subtly pull the iris mid-shot. If you did a lot of event, ENG or reality shooting, that would be a different story, but then I would imagine you'd be using a broadcast lens or something that is made for this purpose.
To your last point though, there are two other big reasons a lot of very sophisticated cameras offer EF mounts:
1. There are other 3rd party still lenses that have, or can be converted to, an EF mount other than Canon that have gorgeous glass that are very popular, and I would even say are much better choices than Canon EF lenses.
The Zeiss ZF and Leica R series for instance, can be "cine-modified" where they de-click the iris (thus eliminating the incremental click stops), install a gear on the focus ring to fit proper follow-focuses, and create a larger front ring to make all the front diameters the same. This largely eliminates the problems inherent in still lenses for motion-picture use. Purely visually speaking, the images that a good modified Leica R lens in excellent condition can produce are on par with some of the best proper cine lenses, so it can represent excellent value for the money as compared to proper cine lenses.
2. Due to the proliferation of such cameras, lensmakers like Canon and Zeiss are offering cine lenses in an EF mount, since many people have simply started to use still lenses on such cameras. These are in many cases very similar optical designs to some of their still lenses but rehoused with proper cine build and function. As such, it is also economical to do this on the lensmakers' part since there is less R&D required on the optical design front.
Erik is right on several fronts there, good post.
Yep, true cine lenses don't "click" through the f-stops, whereas still lenses do. That's not a huge obstacle, though.
To me, the much much bigger issue is focus. Cine lenses are much easier to pull focus than still lenses are. That's simply because of the range of travel of the focus ring. With a still lens, you only have to turn the focus ring a very short distance (usually 1/8th to 1/5th of a full barrel turn) to go from the nearest focus point all the way to infinity. With a cine lens, it's almost a full barrel turn to go through the full range. If you are shooting wide open with a very shallow depth of field, with a still lens that can make it almost impossible to pull a good focus on a moving subject because the ring has to be turned in such tiny miniscule increments... whereas with a cine lens you have much more room for error because you're turning the ring much more.
Also, unless they are very very high-end lenses, almost all still lenses will breathe, whereas cine lenses don't. That's not a big deal until you are doing a lot of focus pulls or rack focusing... and then the breathing stands out like a sore thumb.
Erik is also right about the Leica glass... it's awesome. My current set of primes started life as Lieca/Leitz still lenses... until a previous owner (a DP of some note) somehow got Panavision to rebarrel them years ago (and that was not just remounting to PL, but a full rebarrel, so they are true cine primes now). The glass is just incredible.
Fantastic Plastic Entertainment, Inc.
Samyang sells cheep primes that rivals most top end lenses. They sell cine lenses as well where you can manually pull the aperture ring smoothly. I have a samyang and took out the mechanism that causes the clicks. Never looked back. :) If their is a will their is a way.
Rokinon, which is the same brand as Bowen, and Samyang, has just introduced a new line of cine primes for dslr shooters called xeen. The aperture ring is smooth and and the focus ring has a long throw. But if you want a real cheap fix to your problem you could use a variable polarizer/nd filter. It's actually better than closing your iris because your depth of field doesn't change.