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I have never interacted with a lens that has a collar, so I'm not completely sure what these do.

If I see a picture of a lens and it has a collar, what does that mean? Presumably it means that the lens is heavy (and probably also large). But does it mean the lens can only be used on a tripod? As in, if you use it without a tripod, the weight will snap the camera in half or something? Or is it merely that it wouldn't be very comfortable to use without a tripod? Are you supposed to carry the camera by the lens collar while walking around? For that matter, is it even a good idea to fit an 8 Kg lens on a bottom-of-the-range DSLR body in the first place?

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If a lens has a collar, then it's a sign you should support the weight of the lens & body combination by the lens.

  • When handholding the lens & camera, always keep your left hand holding the lens (i.e., holding the zoom or focus ring, or holding the barrel if you are autofocusing).

  • When using a tripod or monopod, use the collar's tripod mount, not the camera body's tripod mount.

Some of the smallest collar-equipped lenses are possibly OK to carry and hold just by supporting the body, but realize that lenses with larger glass further from the body put lots of strain on the camera's lens mount.

For that matter, is it even a good idea to fit an 8 Kg lens on a bottom-of-the-range DSLR body in the first place?

In that case, you're really mounting the camera on the lens, rather than the lens on the camera. Plenty of wildlife and bird photographers use lower-end DSLRs with crop sensors on large telephoto lenses, to give them extra "reach".

But does it mean the lens can only be used on a tripod? As in, if you use it without a tripod, the weight will snap the camera in half or something?

You probably won't snap the lens mount in half, but you could bend it if you mounted a heavy lens to the camera and didn't support the lens.

Common sense applies here. If the camera and lens are awkward to hold by the camera body alone because the length & weight of the lens strains your wrists, then that strain is also felt by the camera's lens mount. If the system feels more balanced when holding it by the lens, then it will also be more balanced when mounting the lens to a tripod rather mounting the camera body to the tripod. If it feels wrong, then it almost certainly is wrong.

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    +1. It may be worth also mentioning it's the pivotal force of the lens. There isn't much pivotal force on the camera body because it's depth from the lens mount is quite small, whereas the depth from the lens mount to the front of the lens where a lot of the biggest optical elements are is greater. Like the normal forces of levers – laurencemadill Apr 21 '17 at 14:31
  • So what you're saying is, if you hold the camera body and try to counteract the massive torque forces with your bare hands, you might break it, but if you hold the object how a normal human would hold it (i.e., one hand on the camera body and one on the far end of the lens), it's fine to hand-hold it. (?) (Unless you buy the Sigma 200-500mm f/2.8 or something...) – MathematicalOrchid Apr 21 '17 at 14:36
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    @MathematicalOrchid Indeed. Even for some lenses without collars, I would recommend supporting the lens. For instance, my Nikon 28-300mm superzoom is compact enough at 28mm, but at 300mm, it gets to be long enough that it feels awkward to support only by the body. That extension and weight make for a shaky image even on a sturdy tripod, because it's not well-balanced from a dynamics standpoint. – scottbb Apr 21 '17 at 14:47
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    also worth mentioning that if lens has strap loops, you should use those to carry lens+camera on your neck, not camera's – aaaaa says reinstate Monica Apr 21 '17 at 16:22
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    Even if a larger lens doesn't have strap loops, many straps can be attached to the lens' tripod collar via the 1/4-20 threads. – Michael C Apr 23 '17 at 15:57
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Lens collars serve two purposes that are both directly related to the weight and the distribution of that weight in a lens and the camera to which it is attached.

  • From a photographic standpoint the purpose of a lens collar is to provide an attachment near the balance point of a camera/lens system. If the center of gravity/center of mass of a camera and lens is located in the lens, rather than in the camera body, then an attachment point is needed for the lens in order to use the camera and lens on a tripod.
  • From an engineering standpoint the purpose of a lens collar is to provide a way to support a camera/lens system that does not place torque that exceeds design specifications on the connection between the camera and lens. If the center of gravity/center of mass of a camera and lens is located in the lens, rather than in the camera body, then supporting the camera/lens combination via the lens will place less stress on the mount assemblies of both the camera and lens than supporting such a combination via the camera.

In practice the first consideration listed above pretty much always becomes an issue well before the second does. Failure to mount the camera near the center of gravity makes it unstable and will cause a tripod head to drift as it succumbs to the force of gravity. That's if the tripod itself doesn't fall over due to the unbalanced load placed upon it. Even when shooting handheld, the camera will be far more unstable if it is not held in a way that supports it near the center of gravity.

Perhaps the simplest way of looking at it for handheld cameras is this:

If the lens weighs as much as or more than the camera, then you don't really attach the lens to the camera. Instead, treat it as attaching the camera to the lens.

With larger camera/lens systems, such as full size broadcast television cameras or digital cinema cameras, both the camera and lens are often supported by the mounting rigs with which they are used.

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When you mount a camera on a tripod all the forces are translated to that point.

For "small" or "light" lenses the centre of mass is somewhere in the camera body or near to it.

When the lens is heavy or long, attaching it to the camera moves the centre forward and the weight loads the lens mount heavily. When you use the collar properly, the centre of mass is above the screw and the lens mount is loaded by the camera body mass. Note, that momentum matters; the further the center of mass is, the higher momentum the mass generates.

If I see a picture of a lens and it has a collar, what does that mean?

It does that the momentum caused by the lens supported by the body only is higher than momentum caused by the body supported by the lens. When using tripod, use the collar; when carying the camera, hold the lens rather the body.

Presumably it means that the lens is heavy (and probably also large). But does it mean the lens can only be used on a tripod?

It may seem so. The lens can be used as any other lens. When held wrong its weigt can damage the lens mount on the body.

As in, if you use it without a tripod, the weight will snap the camera in half or something?

If held improperly (holding the body only) or attached to a tripod using body mount, it may damage (bend) the lens mount.

Or is it merely that it wouldn't be very comfortable to use without a tripod?

The lens may be heavier than the set lenses. Longer sessions may be incomfortable because you can get tired. It can be hard to shoot with slower shutter as well.

Can I mount 8kg lens to bottom-of-the-range DSLR?

Yes, there is no objection. As @scotbb noted, allways hold the lens by your left hand and support its weight. When using tripod, do small test. Place the camera on a table; If it leans forward do use the collar, if it rests on the body's base you may use the body mount.

Do allways* support the lens with your left hand, no matter what lens you are using - it is code of practice. Pancake or super-tele; it doesn't mind. If I'm using small lens I support both lens and the body with my left hand.

When the lens is supported, there are weaker loads on the lens mount and the camera is more stable.

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I have never interacted with a lens that has a collar, so I'm not completely sure what these do.

The "collar" is also known as a tripod mounting ring, and that term better describes the main function of the device. The ring does two things:

  1. It supports the body of the lens and thereby reduces the strain on both halves of the lens mount.

  2. It puts the tripod mounting point close to the center of mass of the lens+camera combination. If you mount the body to a tripod and then attach a heavy lens, the weight of the lens and the distance between the mount and the center of mass will mean that a lot of torque (rotational force) is applied to the mount. This could cause the camera to tend to tilt downward, or it could damage the mounting point on the camera body, or it could cause a small tripod to tip over. Moving the mounting point closer to the center of mass eliminates that force and solves those problems.

For that matter, is it even a good idea to fit an 8 Kg lens on a bottom-of-the-range DSLR body in the first place?

As long as you support the weight of the lens properly, e.g. by using the ring, even a cheap camera should work fine with a heavy lens.

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