Orquid "Phoenix"

Orquid "Phoenix"

by ceinmart

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I'm shooting some video and I'm renting a Zeiss CP.2 50mm which is a whopping 2 pound lens. I'd like to mount it on a Canon 7D. Will the lens need some sort of additional support apparatus (i.e. the lens won't fall off due to the weight)?

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Two pounds isn't a heavy lens. Your 7D has a magnesium body, and the lens mount is attached to that. If you're able to detach the two, you have bigger problems on your hands. –  Blrfl Apr 12 '13 at 14:17
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3 Answers

up vote 5 down vote accepted

That's about the same weight as the Canon 85mm f/1.2 lens (and the old 50mm f/1.0), neither of which use a tripod socket/collar, so no. I might be wary of the lens on the bottom-of-the-line entry-level DSLRs (where the lens mount is not nearly as strongly attached to the camera frame, such as it is), especially if I were the type who likes to wander around with a tripod-mounted camera carried over the shoulder like a soldier on parade, but it would be no problem at all on a 7D or better.

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That combo should be fine as suggested above, however the actual deciding factor for all lenses is not the WEIGHT of the lens, but the TORQUE applied to the mount.

Torque is the actual pulling/twisting force, which is (basically) weight X distance. (also the lens's centre of gravity has a large effect on this calculation, it is NOT simply length of lens X weight)

For example a very long telephoto that weighs 2KG would apply FAR more torque to the mount than a very short 2KG prime lens.

My general rule of thumb is (on a pro / semi-pro grade camera body) - if the lens manufacturer fits it with a handle, use it (so the camera body only has to cope with its own weight. You either mount the lens to the camera, or the camera to the lens :-)

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The lens in question is only 8cm long. Considering all of the glass is within about 4cm of the flange, its center of gravity is most likely closer to the mounting flange that the 7D's CoG is. Any conventionally designed lens long enough for the torque to exceed the design parameters of the 7D will weigh considerably more than two pounds (less than 1kg). –  Michael Clark Apr 12 '13 at 10:47
    
Yes. correct :-) –  Darkcat Studios Apr 13 '13 at 19:36
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The lens still weighs less than the camera. Barely. This is significant because the mount flange is designed to handle at least that much weight so that the camera will not place too much stress on the connection when a much heavier lens is being supported by a tripod or monopod and the camera body is hanging unsupported from the lens.

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You can't universally apply the rule that lenses that weigh less than the camera are ok, as it's more about the turning moment (torque) than the weight, the camera body centre of mass is very close to the mount and therefore exerts a small moment, a lens of the same weight that was much longer and had most of the weight at the front would put far more stress on the mount. –  Matt Grum Apr 12 '13 at 8:30
    
What you say is true, but for all practical concerns a conventionally designed lens will need to weigh considerably more than two pounds to be long enough for the torque to be enough to damage the mounting flange. This question asked about a specific lens that isn't very long and weighs no more than the body it is mounted on. The mounting flange on the 7D is considerably stronger than the 3-5 inch-pounds that is needed to support the 7D mounted to a larger lens. If the question had been about a five pound lens 12 or more inches long we would be appropriately measuring torque. –  Michael Clark Apr 12 '13 at 10:37
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