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One or the other material is used in the top part of photography carbon fiber tripods.

But which is better for damping vibration, a magnesium cast or an aluminum alloy?

If possible, please provide evidence based answer(URL).

UPDATE:

Let me elaborate please. Top spider/Apex and leg joints of carbon fiber tripods are the main areas of the tripod where either magnesium or aluminum, can be used. Just assume that, there are two similar carbon fiber tripods in every way, except at their top spider & leg joints (the assumption is to neutralise other factors).

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  • Related : What should I pay attention to when choosing a tripod?,
    – Olivier
    Sep 6, 2016 at 16:37
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    I recall a conversation about tripod and vibration. The conclusion was: There is no standard test to characterize tripod vibration. I'm pretty sure you won't get a definitive answer, it's probably depends a lot of the design.
    – Olivier
    Sep 6, 2016 at 16:41
  • Related/duplicate (see above comment) : What properties should I look for to judge tripod quality?, extract : Aluminum is usually the cheap option, they are cost effective, but not very light or great at dampening vibrations. Carbon fiber is typically the preferred material, as it is light, solid, and dampens vibrations
    – Olivier
    Sep 6, 2016 at 16:42
  • Just extended my query for better clarity. Thanks all.
    – Alhytham
    Sep 6, 2016 at 20:08
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    What is the vibration source? Are you purely concerned with mech actions from the camera, or is your tripod going to be mounted on, say, a truck with the motor running? But I do have to warn you that vibration dampening is a highly frequency-sensitive problem, and a combination of materials and structure which works in one band will fail miserably in another band.
    – Carl Witthoft
    Sep 7, 2016 at 11:35

3 Answers 3

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TL;DR: You can't really optimize the tripod apex for vibration reduction, just the legs.

Note: I've also heard the apex referred to as a spider. It's the (usually) single piece where the legs come together — the center structure.

I think you're worrying about optimizing the wrong part (i.e., the apex) for vibration. They are either cast, or milled from from a billet piece of metal. The geometry of the apex is compact and stiff. Its whole point is to be strong, in order to hold up to the stresses the legs impart on it.

A material's ability to transmit and/or dampen vibration is from deformation — the material literally elongates, bends, "squeezes", etc., tiny amounts. Absorbing vibrations is just converting kinetic energy (i.e., motion) into heat energy (albeit an imperceptible amount).

The legs of a tripod are designed to be as light as possible while spanning a long distance (relative to the cross-sectional diameter and thickness of the tubing wall). It just so happens that the choice of material in the legs also can have vibration damping characteristics, but that really just overcomes the fact that the issue of vibration was created by the long/thin geometry of the leg to begin with!

The vibrations you're hoping to reduce are actually created by the legs. As long & thin structures, they are basically oscillators "pinned" or fixed at both ends, with a certain characteristic frequency (probably below about 20 Hz). External forces, such as wind passing over the legs induce them to oscillate at their natural frequency. This oscillation is identical in nature to large structures, such as the infamous Tacoma Narrows Bridge (that literally oscillated to the point of self-destruction). Think about an oscillating suspension bridge for a moment: what can you possibly do at the nodes (i.e., the ends of the bridge) to stop the middle from oscillating? You can't. You have to address the problem along the length and/or in the middle, where the generated forces are the largest (and by reflection, where you have the most ability to impart counterforces).

Thus, it is the very material of the tripod's legs that diminishes the vibration they produce. The apex has no ability to absorb the vibrations, because it is one of the endpoints, the upper node, of each leg.

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    Great answer. Minor thing: I wouldn't call the legs fixed at both ends as the top part can still move around. I'd say it's more like an upright pendulum. Either way, I agree that the material of the legs has more influence. The property of the top part that plays a role in vibration reduction is its mass I'd say, not its material. The mass can easily be improved by adding additional weight in the form of rocks in some bag hanging from the top part, for example.
    – null
    Sep 7, 2016 at 8:53
  • @null It seems to me that from the point of view of any single leg, the top part is pretty limited in range of motion by virtue of resting on the other 2 legs. That, and the top part's higher mass with respect to the lighter distributed mass of each leg makes it mostly fixed. Kinda like the towers in tall suspension bridges: they're considered fixed at both ends (the top fixed point is due the tension in the top cable). The Akashi Kaikyo Bridge has tuned mass dampers a little more than halfway up, inside each tower, to counteract sway.
    – scottbb ♦
    Sep 7, 2016 at 12:10
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Taken from http://www.eng-tips.com/viewthread.cfm?qid=77876, answer to the question Can anybody tell me what are the advantages in using magnesium [for electronic fixture] ? (highlights are mine) :

Magnesium alloy is usually touted as having a higher specific strength than aluminum alloy, but of course it depends somewhat on which alloys you pick. Although magnesium alloys have a considerably lower density, specific stiffness of magnesium alloys is about the same as aluminum alloys, so it's not immediately obvious what the advantages would be from a vibration point of view, at least to me. However, magnesium alloy is also supposed to provide higher damping capacity than aluminum alloy, so perhaps that is one reason. On the other hand, most of the damping present in structures has nothing to do with the material properties, but comes from other sources, such as bolted joints etc. Then again, because of magnesium's higher specific strength, it may be possible to use thinner sections than would otherwise be practical, and thereby obtain better dynamic stiffness of components than you could with aluminum.

So as Scottbb said in his comment, I'm pretty sure the choice of material has not a lot of influence about damping vibration, as long as the joints are designed/produced why the same quality.

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  • That's great Olivier. Appreciate your contribution. Thanks.
    – Alhytham
    Sep 6, 2016 at 22:02
  • I will try to make a vibration analysis tomorrow with a basic tubular structure (Catia + Ansys).
    – Olivier
    Sep 6, 2016 at 22:11
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I've done some experiments on camera/tripod motion. In particular the mechanical vibration induced by mirror slap and even shutter motion. One technique is to put a small pinhole in a black sheet of paper with a bright light behind it. Then you can take pictures of it and see how much deviation occurs with different setups like using mirror hold and different exposure times. If you adjust the light levels so the pixels don't saturate, you can then use dcraw and bypass the CFA interpolation for more precision, this can show motion down to fractions of a pixel. By selecting exposure times from 1/5 to 1/100th second one can determine roughly the resonances activated. Also, by using a range of long exposures from 1/2 to 10 seconds one can estimate how long an exposure needs to be so the large majority of the exposure occurs after mechanical resonances have died off.

I've also experimented with using surveyor's tripods, which are bulky but very stable. They tend to reduce the "Q" as well as deviations but are a bit more trouble being rather bulky

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