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 p.1 #9 · Canon to make pro movie lenses? | |
Mike Mahoney wrote:
I'm unsure of what the differences between regular lenses and DSLR movie lenses would be? Seems current lens lineup and sensor size and attendent IQ are the two main reasons for film industry 5D2 purchases.
Good movie lenses, as a whole, tend to be far superior to still photography lenses in most respects. It loses out in size, weight and price. Movie lenses, are big, heavy and expensive.
First and foremost, the lenses tend to be much quieter than still lenses. Still lenses make a lot of noise when they zoom and focus. Even the aperture blades make noise.
Most lenses made for movies on a professional level are manual. The focusing rings on movie lenses are definitely have much better dampening with a longer throw for more precise focus. The manual aperture is similar to the focusing ring (I don't think they have detents) allowing for on-the-fly aperture control (if a camera goes from dim to bright in a scene they would want to control the aperture rather than the frame rate).
Still lenses tend to have focus breathing, which is unattractive for movie making.
Movie lenses are also measured in T-stops. Where the F-stop is the size of the aperture, the T-stop is the amount of light hitting the film plane. Lens coatings and glass will absorb or reflect some amount of light. The T-stop will give you a value (in an f-stop ratio number) of the actual light hitting a sensor. For instance, a lens may be 100mm f/2, T/2.2, where a third stop of light is absorbed by the glass itself.
Moreover, most movie lenses are also engineered to give consistent color between lenses so that you can film a movie with multiple focal lengths and not have to worry about color correction in post.
It's also important to note that movie lenses are huge. I'm guessing the extra size is meant to address optical defects that smaller pieces of glass may exhibit.
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