telephoto - Is this a tripod head over capacity or just how they work?

I use my Sirui T-005X tripod with a Sirui C-10X head. When I place my Nikon 300mm f4 AF lens on it, I slide it on and tighten both the plate lock and the position on the ball head. After letting go, I notice that the camera and lens move up a bit up (a few mm but at most 1cm) and finally stops moving. Afterwards I use a remote cable release to take a shot.

I assume when I hold it I'm pushing the lens and body a bit down? I'm use to compensating for this movement but I never bothered to ask until now.

I do not notice it with any lighter lens, although I don't have any other lens with a collar to test it.

Is this a sign that I need a better ball head (or other tripod head) or is this how ball heads work with heavy telephoto lens?

Answer

In my opinion, that ballhead is too lightweight for uses beyond holding smaller DSLRs with shorter/lighter lenses. Many tripod and ballhead manufacturers overstate their "rated" weight.

For instance, the Sirui C-10X says it has a capacity of 28.7 lbs. But what is that, in photographic equipment terms? A Nikon D810 weighs 1.98 lb (990 g). With a 600 mm ƒ/4G ED coming in at 11.16 lb (5.1 kg), the total camera + lens combination weighs 13.14 lb (6 kg), which is just half the rated capacity of the Sirui C-10X. I would not put a 600 ƒ/4 + D810 anywhere near that ballhead. Sure, it will probably clamp and hold the lens when everything is balanced. But if the system were tilted to provide an unbalanced torque on the ballhead, would you be confident the ball wouldn't slip? Not me.

So where is the "real" or practical limit of the ballhead? I have no idea. I don't believe in any of the "specs" at all, because I haven't seen a ballhead manufacturer publish testable, measurable numbers (i.e., something like "max holding torque"). When it comes to minimizing vibration, deflection, or drift, in general, more mass is better. Mass dampens vibrations. Assuming like metals, more mass means larger geometry (such as larger balls in the clamp) which provides longer moment arms to apply force (i.e., more resistant to torques applied by heavy loads).

If your use of the 300mm ƒ/4 (which is a pretty short and light lens for its reach and aperture) indicates you will be using more lenses of that general size or larger, then yes, you will need a better ballhead. You don't have to spend as much as a Really Right Stuff BH-55, but when it comes to stability of mount, that's the approximate size you should be looking at.