NikonGear'23
Gear Talk => Other => Topic started by: basker on March 15, 2018, 23:54:08
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I understand that tripod apex hinge size affects stability.
Does the spacing from centerline to hinges matter?
Thank you,
Sam
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If you imagine the triangle formed by any two of the tripod legs extended up beyond the hinges, the closer the mass of the ballhead + camera + lens is to being inside that triangle, the more stable the tripod. So, the further the hinges are from the centre, the higher the apex of the imaginary triangle, and the more of the load is inside the triangle. The downside is that the plate that the hinges attach to has to be stronger and therefore heavier.
The alternative way to get the centre of mass inside the triangle is to hang a weight inside the tripod.
I do not think that tripod hinge size does anything independently of the diameter of the tripod legs. Thicker legs require thicker hinges, and thicker legs are more rigid.
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The alternative way to get the centre of mass inside the triangle is to hang a weight inside the tripod.
I do not think that tripod hinge size does anything independently of the diameter of the tripod legs. Thicker legs require thicker hinges, and thicker legs are more rigid.
I'm not sure about hanging weight as it can swing causing its own problems but the flexibility of smallest or lowest legs of a tripod are easily a tripod's achilles heel. I own an original C. M. Marchioni Tiltall and Bogen 3021 that suffer this way. I guess they are good to about 135mm.
When I was really green. I tried to use the Tiltall with a 600/9.0 Vivitar Series 1. I thought the lens was a dog. :D :D :D
My Nikon F3 and later performed much better my Nikon F2As, FM2n and FE2. The latter show more vibration on mirror up and shutter open on the tripods with more flexible lower legs. Not using the last tripod section helps quite a bit and spreading the legs of the 3021 helps even more.
Dave Hartman
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If you imagine the triangle formed by any two of the tripod legs extended up beyond the hinges...
I do not think that tripod hinge size does anything independently of the diameter of the tripod legs...
Les,
Looking at the RRS apex conversion kit, I became fixated on a stability question that I could not answer. Thanks for helping me break out.
Looking at my tripod as three pairs of legs instead of just three legs is a clear and quite interesting concept. Your posts give me wider perspective.
Sam
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If you imagine the triangle formed by any two of the tripod legs extended up beyond the hinges, the closer the mass of the ballhead + camera + lens is to being inside that triangle, the more stable the tripod. So, the further the hinges are from the centre, the higher the apex of the imaginary triangle, and the more of the load is inside the triangle. The downside is that the plate that the hinges attach to has to be stronger and therefore heavier.
The alternative way to get the centre of mass inside the triangle is to hang a weight inside the tripod.
Another way to get the center of mass inside this triangle is to spread the tripod legs less. I can't see how that is making it more stable…
My experience is spreading the legs more does help with stability, but it makes this triangle smaller, so it push the center of gravity longer outside.
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...the flexibility of smallest or lowest legs of a tripod are easily a tripod's achilles heel...
Dave Hartman
Dave,
Good to hear from you. My tripod (RRS 24L) does feel flimsier with all four sections extended. I do it sometimes to avoid crouching or shoot upwards, but I agree shorter seems better. Still pretty nice for a lightweight system. I rarely use it with a lens above 135mm. I also agree that a much longer lens would prefer a heavier tripod.
I admit that I too have an old Bogen :). The center column can be rotated, so I put a monopod head on it to add tilt. Looks kind of cute with a Coolpix A on it.
Sam
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It is a common mistake to assume "heavier is better" when discussing tripods. A tripod's stability relates to its construction principles and torsional rigidity more than weight. The tripods I'm using range from 1.2 kg upwards and all of them hold a 600/4 or similar with ease (we're talking about Sachtler tripods here).
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Another way to get the center of mass inside this triangle is to spread the tripod legs less. I can't see how that is making it more stable…
My experience is spreading the legs more does help with stability, but it makes this triangle smaller, so it push the center of gravity longer outside.
If you decompose the vector of the gravity into the vector component along the tripod leg (a) and the one perpendicular to the leg (b), (a) will be stronger while (b) will be weaker when the leg is spread less. The vector component (b), in effect, bends the leg towards inside of the tripod. That may be why the tripod feels more stable when the leg is spread less.
On the other hand, the stability against the torsional force can be weaker when the legs are spread less. So, the best total balance of the stability may change according to the shooting situations.
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It is a common mistake to assume "heavier is better" when discussing tripods. A tripod's stability relates to its construction principles and torsional rigidity more than weight. The tripods I'm using range from 1.2 kg upwards and all of them hold a 600/4 or similar with ease (we're talking about Sachtler tripods here).
Bjørn,
Seeing pictures of your tripod is how I got the idea that hinge width is a big deal, especially in torsion. My tripod, including the ballhead and clamp, is about 2 kg and fits my 70 inch eye height. If I did, miraculously, get a 600/4, there would be an equally miraculous fluid head Sachtler attached to it. No disparagement was intended when I assumed that setup would be heavier. I misspoke, I should have said "heavy duty" to be accurate, and I do love hearing from you.
Best wishes for your new home,
Sam
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Think this is a fairly steady position to support the camera. ;)
I used it with a radio remote to shoot behind goal action while I was on the sideline. The flash was so I knew it was actually making exposures.
Inverting the image in pp of course. ::)
(https://farm1.staticflickr.com/788/25976585337_39cb637a4c_b.jpg)
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Think this is a fairly steady position to support the camera. ;)
A poster for "Inside the Apex!" Love it when I see something and just know it works.
Looks like it walked there during "War of the Worlds." :)
Thank you,
Sam
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;D ;D ;D
Well I wanted the camera low for drama and in case a ball (or player), hit the tripod I wanted protection for the D1, which back then was still precious and the 18-35 lens, which still is.
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My Tiltall can resonate for up to 45 seconds after the mirror comes up. I would guess this was an F2 but I don't remember. This is not an endearing feature.
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A tripod's stability relates to its construction principles and torsional rigidity more than weight.
Perhaps stability is being used to mean different things here. Stability meaning resistance to being pushed over, as by a wind, is related to weight and to the geometry. Torsional rigidity has nothing to do with stability meaning resistance to being pushed over, within the range of forces a photographer is likely to encounter.
Torsional rigidity and vibration damping also relate to weight, because both depend on the elastic modulus of the material and the mass of material. For practical purposes, any desired level of rigidity can be achieved with any material if you use enough of it. Where design comes in is (1) the diameter of the legs, assuming they are hollow, because larger diameter means more rigidity for the same weight, and (2) in the joints between leg sections, because the joints are always much weaker in bending than in compression, so their ability to support a weight along the axis of the legs is excellent, their ability to resist a force applied to one side may be poor.
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'Stability' as in the sense of being able to hold a camera/lens stable over time. Torsional rigidity means less proneness to being twisted during the exposure.
The "crutches" construction makes say a Sachtler quite light in weight compared to traditional tripods, yet it provides a very stable support. I have used these tripods for decades so am pretty familiar with their behaviour in the field. They also have the additional feature of working well immersed in mud, snow, or water.
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(1) the diameter of the legs, assuming they are hollow, because larger diameter means more rigidity for the same weight
(2) in the joints between leg sections, because the joints are always much weaker in bending than in compression, so their ability to support a weight along the axis of the legs is excellent, their ability to resist a force applied to one side may be poor.
I am tall and well aged. Adapting to awkward viewfinder placement is extremely difficult. So a third factor, longer tripod legs, arises to push the limits of 1 & 2.
Earlier I said that extending the fourth section makes a difference. Now I wonder what causes that difference. Is it the smaller tube, the additional (smaller) joint or the increased total length? My first guess is all of those, so I have a lot more thinking to do.
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This mays seem like silly and going off at a tangent but I once had a strange experience which I have never explained.
Many years ago I leant a ladder against a stone built shed, the ladder was about 12 feet long and the shed about 9 feet high. The ladder started to vibrate, like buzzing? I don't remember the details but even if I moved it then put it back in the same place, it vibrated. You could feel the vibrations with your hand and hear them, there was no wind to speak of.
This experience has led me to think that on occasions some things may vibrate in harmony with their surroundings. I don't pretend to understand it but I do believe there can be this phenomenon. A ladder and a tripod are not dissimilar and although I realise we are talking stability, not vibrations, I just wonder if sometimes things have a natural harmony and can spontaneously vibrate without us realising, causing blurry images.
I have been surprised at the readings I get with the seismometer app on my iPhone when placed in apparently rock solid locations. I realise calibration of these sorts of devices is important but the fact that it's picking up vibrations, apparently from nowhere, maybe they can be amplified by something like a metal or even a wooden tripod.
In my eyes, heavy is better because it needs more energy to cause vibrations in a heavier object. If the energy is constant, increasing the mass should reduce the amplitude of the vibrations and probably the frequency too.
No, I haven't been near magic mushrooms! ::)
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'Stability' as in the sense of being able to hold a camera/lens stable over time. Torsional rigidity means less proneness to being twisted during the exposure.
The "crutches" construction makes say a Sachtler quite light in weight compared to traditional tripods, yet it provides a very stable support. I have used these tripods for decades so am pretty familiar with their behaviour in the field. They also have the additional feature of working well immersed in mud, snow, or water.
With a properly balanced load, the single legs of a tripod have all forces in line with the leg, so no bending is encountered with a vertical load, but there are often rotational loads placed on tripod heads, especially with panning of a video head or similar.
The leg construction on Sachtlers resists bending due to rotation around the head and is a superior design to just adding fatter legs to an ordinary tripod. You see similar designs in surveying tripods where angular error is very much to be avoided.
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'Stability' as in the sense of being able to hold a camera/lens stable over time. Torsional rigidity means less proneness to being twisted during the exposure.
That was my intended meaning for stability in the original post, and that is exactly what I hoped torsional rigidity meant. Whenever I mount a camera via quick release plate and with the lens cantilevered off the body, I have to be wary of vibration in any plane. I must try to understand the process and learn to best use what I have. I want to get a true image, no matter how homely or mundane the subject may be.
The "crutches" construction makes say a Sachtler quite light in weight compared to traditional tripods, yet it provides a very stable support...
I can see that. Either the leg or the hinge will be a weaker link. Best case is when both are so strong it does not matter.
Clearly, the conventional tripod has limitations, but is it completely useless? Thinking that makes my wallet ache. :)
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If the substrate is soft, springy, or soggy, and the tripod doesn't make good contact to the ground, one can add a lot of weight to a tripod and still have it wobbling around :D
My setup for the first Venus Transit (2004) involved three Sachtler tripods, from front to rear these were Sachtler ENG 2 CF, DA-100L, and DA-75L, respectively. These weigh in around 2 kg without the head.
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The small Sachtler for travels and close-to-ground work weighs just 1.2 kg. With a proper head on it, there is no problem with a 600/4 or similar. Properly set up it has extreme torsional rigidity and stabilty.
(I made it from an ordinary DA-75L by cutting-off the legs)
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Think this is a fairly steady position to support the camera. ;)
I'd be concerned about resonance in the hanging center column. I would shorten the legs of the tripod and use less of the center column.
Dave
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Deleted
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The various incarnations of DA-75L have been very popular amongst Norwegian nature photographers for many years. There are 2- or 3-section models, material of aluminium (the "classic" model) or carbon fibre, and with or without a "quick release" mechanism. Cutting down the carbon fibre models require more skill and it's easier to break a leg as it were; however, this material makes the tripod even lighter and more pleasant to handle in the winter.
Personally, I now prefer the ENG-2 series as I mainly work out of a car.
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'Stability' as in the sense of being able to hold a camera/lens stable over time. Torsional rigidity means less proneness to being twisted during the exposure.
What twisting force is acting during or near exposure? The photographer's finger on the shutter - unless she uses a remote release - but to reduce the effect of that force what is needed is to reduce the length of the "lever" - the distance between the shutter release and the axis of support. The 35mm design, with the shutter button high and far to one side, is a problem in this respect - the medium format design, with the shutter button low on the front of the camera is better - but what helps with a 35mm camera is a quick release plate and tripod head that extend as near as possible to the line of the shutter press (unfortunately, Nikons have the battery on that side so the plate cannot be as long as would be ideal). A long lens also creates a twisting force - although not any more during exposure - but the remedy is the same: minimise the rotational force by shortening the distance between the axis of support and the weight. That is why large diameter ballheads, and flatter ballheads, are better. Small changes in the length of the lever make a big difference, because the bending of a beam supported at one end by a force applied to the other end is inversely proportional to the cube of its length.
Sagging over time is a flaw of the ballhead concept that depends on friction between the ball and a flexible cup to prevent movement, because it won't.
As far as the crutch design is concerned, if it could provide the same rigidity with less weight it would be universally used where stiffness has to be maximised and weight minimised - bicycle and motorbike frames, eg - and it is not. There is a good reason for that: the stiffness of a hollow tube is proportional to the fourth power of its diameter, while its weight is proportional to the square of its diameter, so, for the same weight of material, a single tube is much stiffer than two narrower tubes.
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There are two possible approaches: theoretic or practical. As my experience shows the Sachtlers work much better than the Gitzos I used earlier, the choice is easy They support my gear in a superior manner, are more light weight, far more versatile in how they can be set up in the field, and stand adverse conditions than would destroy a Gitzo.
If theory is contradicted by practical observations, the theory needs to be improved.
I once worked with this TV videographer on an assignment and she didn't bat an eyelid about submersing her Sachtler tripod to get the required camera position.
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As far as the crutch design is concerned, if it could provide the same rigidity with less weight it would be universally used where stiffness has to be maximised and weight minimised - bicycle and motorbike frames, eg - and it is not. There is a good reason for that: the stiffness of a hollow tube is proportional to the fourth power of its diameter, while its weight is proportional to the square of its diameter, so, for the same weight of material, a single tube is much stiffer than two narrower tubes.
Please look at the rear triangle of any bicycle and imagine downtube is the tripod head, axle is where the foot of the tripod leg is.
Likewise on many motorcycle frames at head tube.
The claim that something would be universally used makes no sense when not all use cases are the same. Some are driven by cost, ease of construction, available materials etc.
The triangular leg, and its cousin the flat leg, are used in almost all cases for video and surveying due to their resistance to torsion about the vertical tripod axis. To achieve the same with a single tubular member would require making it bulkier than it needs to be. Beams are “universally” placed with their deepest section oriented in the plane they need to provide most resistance to bending.
Video has this requirement because the camera often pans horizontally against resistance. Surveying equipment has the same requirement because it needs to stay stable in environmental conditions such as wind.
Still cameras can benefit from this rigidity, but it is dependent on the use case and what is considered “good enough”. For some people a monopod or even human tripod is sufficient. So most camera tripods are designed to be light and portable with just enough stiffness for the job at hand. Not all people need a Sactler ENG series tripod, many can’t afford it, and many don’t want to carry it. For long exposures, the resistance to wind caused torsion is a good thing.
As always, suitability for the circumstances at hand should govern choice.
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[quote author=Seapy link=topic=7235.msg116771#msg116771 date=1521317032
This experience has led me to think that on occasions some things may vibrate in harmony with their surroundings.
In my eyes, heavy is better because it needs more energy to cause vibrations in a heavier object. If the energy is constant, increasing the mass should reduce the amplitude of the vibrations and probably the frequency too.
[/quote]
The phenomenon of small vibrations acting on a structure to produce larger amplitude vibrations is resonance. It requires the driving vibration to be in a narrow range near the resonant frequency of the second structure. Any structure can resonate, including tripods. The mass of a structure affects its resonant frequency, but not the amplitude of the resonant vibrations when it is subjected to vibration at its resonant frequency. That is why quite small inciting vibrations can cause catastrophic structural failure of large structures.
If you make a noise - create vibrations - by hitting an object the amplitude of the vibrations (= the loudness of the noise) is less if the stiffness of the material is greater but is not affected by the mass of the object. The frequency of the vibrations (= the pitch of the noise) is reduced by both more stiffness and more mass.
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The triangular leg, and its cousin the flat leg, are used in almost all cases for video and surveying due to their resistance to torsion about the vertical tripod axis.
For long exposures, the resistance to wind caused torsion is a good thing.
Yes, resisting rotational forces requires a different design, but that has nothing to do with stability during still photography.
Wind exerts a force on an object equal to 1/2 x density of air x wind velocity x surface area of the object. A 300mm f/2.8 lens has a surface area of roughly 300 square cm, so if the lens was a flat surface you would need about 50kph of wind for the wind-loading to exceed the 2.9kg weight of the 300/2.8 (plus the lens is not flat, which reduces the wind loading). That sort of wind makes walking difficult, so if your tripod is not inconvenienced by the weight of the lens, wind is not an issue unless you are a specialist cyclone photographer.
Wind can also cause problems because of flutter, but that will be no better with a crutch design than with a single tube design.
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The phenomenon of small vibrations acting on a structure to produce larger amplitude vibrations is resonance. It requires the driving vibration to be in a narrow range near the resonant frequency of the second structure. Any structure can resonate, including tripods. The mass of a structure affects its resonant frequency, but not the amplitude of the resonant vibrations when it is subjected to vibration at its resonant frequency. That is why quite small inciting vibrations can cause catastrophic structural failure of large structures.
If you make a noise - create vibrations - by hitting an object the amplitude of the vibrations (= the loudness of the noise) is less if the stiffness of the material is greater but is not affected by the mass of the object. The frequency of the vibrations (= the pitch of the noise) is reduced by both more stiffness and more mass.
Thank you kindly Les, that is very interesting, I had hoped someone might reply, I realise it's a bit OT, but it is a bit related and also related to the issue Michael had photographing flowers a while back with a resonating floor. My answer to most thing is more mass, but a damping mechanism would probably be more effective in absorbing the energy perhaps?
I suppose a practical example of frequency is a bell, small bells go 'ting-a-ling', large bells go 'BOING'.
If the mirror lifting shakes the tripod that energy has to dissipate before the camera becomes still again. A heavier tripod/camera would still vibrate with the same amplitude, but at a lower frequency, slower. Interesting. How does the mass affects the decay of the energy? More mass longer decay? Or visa versa...
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Yes, resisting rotational forces requires a different design, but that has nothing to do with stability during still photography.
Wind exerts a force on an object equal to 1/2 x density of air x wind velocity x surface area of the object. A 300mm f/2.8 lens has a surface area of roughly 300 square cm, so if the lens was a flat surface you would need about 50kph of wind for the wind-loading to exceed the 2.9kg weight of the 300/2.8 (plus the lens is not flat, which reduces the wind loading). That sort of wind makes walking difficult, so if your tripod is not inconvenienced by the weight of the lens, wind is not an issue unless you are a specialist cyclone photographer.
Wind can also cause problems because of flutter, but that will be no better with a crutch design than with a single tube design.
I don’t think that leg design is a significant factor in keeping the tripod from blowing over. Not sure why you would be considering that as something different. Also note that the wind force usually doesn’t have to be as large as the gravitational force on the camera to make the whole thing fall over. As long as horizontal force due to wind * height of center of mass of camera and tripod is greater than force of gravity * distance from leg to center of mass of tripod, the overturning moment is enough to topple your tripod. (Positing symmetry as a simplifying assumption)
Fluttering in the wind occurs at lower speeds, and is dependent on leg design as it affect stiffness.
Whether those effects are important in your work depends on the nature of your work. For long exposures outdoors in blustery weather they may be. One can certainly get great photos without it.
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...My answer to most thing is more mass, but a damping mechanism would probably be more effective in absorbing the energy perhaps?... If the mirror lifting shakes the tripod that energy has to dissipate before the camera becomes still again. A heavier tripod/camera would still vibrate with the same amplitude, but at a lower frequency, slower. Interesting...
I bought the four section legs to satisfy a height requirement. One rationalization was that an additional lock would give additional damping. Still do not know if that was just fantasy. Imagined uses vs. actual application is a sneaky relative of theory vs. practice.
There are several ways I can shorten the legs, and all of them seem to reduce flexing. Maybe the answer is a folding stool. :) An earlier post shows a youngster kneeling on a pad. A brilliant solution but I might require assistance getting up. :)
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... An earlier post shows a youngster kneeling on a pad. A brilliant solution but I might require assistance getting up. :)
That was in fact me :D although before the hair went grey and other things changed as well. Knee pads are still a great invention whether used on their own or embedded in the trousers workman-style.
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...related to the issue Michael had photographing flowers a while back with a resonating floor...
I wonder if that one got resolved. :-\
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Shooting with really long lenses is the true acid test for tripod support. Here my 1200/11 ED-IF on the Sachtler ENG 2 CF HD with Video 20 Fluid Head. This combination supports the long lens with ease so the user just can concentrate on locating the subject (not always easy, thus having levers to move the head rapidly is essential) and shoot.
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Here my 1200/11 ED-IF on the Sachtler ENG 2 CF HD with Video 20 Fluid Head...
Awe inspiring! Reminds me of a dry old IBM witticism, "there's probably a two week course in Poughkeepsie for that one."
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That was in fact me :D although before the hair went grey and other things changed as well...
Time does fly, but "Modern Excalibur" alone buys you a lifetime pass to my good opinion.
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I don’t think that leg design is a significant factor in keeping the tripod from blowing over. Not sure why you would be considering that as something different. Also note that the wind force usually doesn’t have to be as large as the gravitational force on the camera to make the whole thing fall over. As long as horizontal force due to wind * height of center of mass of camera and tripod is greater than force of gravity * distance from leg to center of mass of tripod, the overturning moment is enough to topple your tripod. (Positing symmetry as a simplifying assumption)
There are two separate issues, with both weight and wind.
One issue is the tripod pivoting around one of its feet and toppling over. For the tripod to pivot around one of its feet the weight of the camera etc has to be lifted against gravity. For the usual arrangement, with the camera etc near the apex of the tripod, and one of the legs in the line of the wind, the wind loading x sine of the angle between the tripod leg and the ground has to exceed the weight of the camera x cosine of the angle between the tripod leg and the ground. What you want to resist toppling is widely splayed tripod legs and more weight. Weight suspended from the tripod works because it lowers the centre of mass and therefore the angle with the ground, and because its own wind loading does not create any lifting force, so the wind loading on the camera alone has to lift the camera plus the suspended weight. Even more effective is attaching the tripod to the ground with tent pegs.
Leg design could affect the likelihood of the tripod blowing over in two ways. One is if the legs bend, but unless you have a very flimsy tripod that would require hurricane force winds. Perhaps more likely is the feet being driven into soft earth or snow, or slipping because you have carbide tips on rock. Where leg design will make a difference is flutter and buffeting, and a multiple tube design will be worse - for the same reason as you get vibration when you partially open a car window.
The second issue is the camera pivoting on the ballhead - ie, pitch in the case of weight and wind from the front or behind, and roll and yaw in the case of wind from the side - more yaw with long lenses. Because the ballhead is symmetrical its ability to resist all those movements is the same, so weight is the same as wind loading as far as the ballhead is concerned.
Another issue, that Bjorn has alluded to, is .
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Les,
You are sort of correct, but also not completely correct. When the moment created by horizontal forces of wind (includes wind against camera, legs, sandbag etc.) is higher than the moment created by gravity around that same point - the downwind leg - the rig will overturn. This is simple physics, but doesn’t really make any difference in leg design choice.
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This is my answer to wind...
The spikes are fitted with foot kickers, so one can stamp them into the ground in soft conditions, the ground here was hard under the grass.
Wastwater, English Lake District. A brief lull, on a VERY windy day.
(https://farm1.staticflickr.com/791/39092033700_8e5e8881d4_b.jpg)
This was one of the photographs I took. The gusts were breathtaking.
(https://farm1.staticflickr.com/797/26029148867_69657920de_b.jpg)
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Surveyor's tripods were all the rage in my neck of the woods until nature photographers switched to Sachtlers instead. A lot less to care in the field :D and properly set up in the same stability league as well.
Nice picture on the Wastwater - I had the impression all water bodies in he Lake District were calm and serene, but obviously I was mistaken :D
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This is my answer to wind...The gusts were breathtaking.
Steely determination, ingenious solution and impressive results, as usual from Robert.
Very cool stuff :)
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The edited statements below are from a tripod vendor's website.
"The longer the focal length is, the more apparent vibration becomes, and the demand for eliminating or preventing that vibration is increased."
"Even though a 300mm/f4 lens might only weigh as much as a 70-200mm/f2.8, you still deal with the same magnification factor in terms of "revealing" the vibration within a system. This may be emphasized by lower mass of the lens, since a lighter setup has less inertial resistance to outside vibration."
"Even when a 400mm magnification factor can be handled by a particular tripod, the weight and bulk of a lens that size may be easier to handle and safer on a broader and more rigid platform system."
Heavier and longer lenses are more demanding, but in my case that does not matter. I think that what I have is adequate if used properly, even though I also want improvement.
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Les,
When the moment created by horizontal forces of wind (includes wind against camera, legs, sandbag etc.) is higher than the moment created by gravity around that same point - the downwind leg - the rig will overturn.
Yes: the conclusions are the same whether you calculate moments or treat gravity and the wind force as vectors normal to the tripod leg and along the tripod leg, whose sizes relate to the sin and cos of the angle the leg makes with the ground.
The reason I would rather think about it in terms of the leg angle is that I think it makes it easier to understand two aspects of using a tripod in windy conditions.
The first is that once a wind gust starts the tipping, and the angle the leg makes with the ground increases, the tipping will continue despite the gust abating, which is why your expletive deleted tripod (or tent) appears to be stable but then tips over suddenly and without warning.
The second is that splaying the tripod legs increases resistance to being tipped over by the wind, but the relationship between how much you splay the legs and increasing stability is not obvious. My Gitzo tripod legs make an angle of about 70 degrees to the ground in their default position, and sin 70 = 0.94 and cos 70 = 0.34. If high wind is the problem, 70 degrees is way too steep. But sin 60 = 0.87 and cos 60 = 0.5, sin 45 = 0.7 = cos 45, sin 30 = 0.5 and cos 30 = 0.87, and sin 15 = 0.26 and cos 15 = 0.96. So going from 70 degrees to 60 degrees does not help all that much, and to make a big difference to stability in high winds you need to get the tripod much lower to the ground. The other side of that coin is that getting much lower to the ground makes it much harder for the legs to support the weight of the camera plus lens. So if you are going to have to work in high winds, you need a tripod that can get low, and you need a much stronger tripod than if you could leave the angle of the legs at 70 degrees.
If the sandbag is suspended to form a pendulum its wind loading displaces the mass away from the vertical. The weight is supported by the tension in the string, that has a vertical component and a horizontal component, and their relative sizes are related to the angle between the string and the vertical. The horizontal component, like the wind loading, has two components, one along the tripod leg and one normal to the tripod leg, and their relative sizes are related to the angle between the tripod leg and the ground. Sin 45 = cos 45 = 0.7, so if the tripod legs form an angle of 45 degrees with the ground and the sandbag is being blown so the string is parallel to the tripod leg (some wind), only 70% x 70% = 049% of the wind-loading on the sandbag is tipping the tripod over. In a more realistic scenario, where the sandbag is only displaced a few degrees, a much smaller proportion of the wind-loading on the sandbag makes a tipping force; eg, if the string is displaced 5 degrees and the tripod leg is at 45 degrees to the ground, the tipping force is 9% x 70% = 6% of the wind loading on the sandbag.
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Thinking out of the box,,, This is quite a stable setup ;D
(https://farm9.staticflickr.com/8843/29441770702_3196a97e43_o.jpg) (https://flic.kr/p/LRELGf)26728876092_1e78dcbfe4_o (https://flic.kr/p/LRELGf) by Erik Gunst Lund (https://www.flickr.com/photos/erik_lund/), on Flickr
(https://farm2.staticflickr.com/1642/25977834774_a11647de5a_h.jpg) (https://flic.kr/p/Fzzce1)L1043808 (https://flic.kr/p/Fzzce1) by Erik Gunst Lund (https://www.flickr.com/photos/erik_lund/), on Flickr
(https://farm9.staticflickr.com/8445/29261008430_ec5f44c16c_h.jpg) (https://flic.kr/p/LzGjnm)_EGL2762 (https://flic.kr/p/LzGjnm) by Erik Gunst Lund (https://www.flickr.com/photos/erik_lund/), on Flickr
Be aware of how and where you attach all of the elements of a 'tripod'
Camera and or lens
Lens Plate and or rail
Clamp
Head
Tripod top base
Legs, upper and lower
Feet
Ground
All of these parts and interfaces between these are more or less equally important for stiffness and vibrations.
Consider if it is possible to leave out parts. For convenience a dovetail system is nice but not always cleaver or absolutely needed.
How 'well' is the interface between the leg sections designed.
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"The longer the focal length is, the more apparent vibration becomes, and the demand for eliminating or preventing that vibration is increased."
"Even though a 300mm/f4 lens might only weigh as much as a 70-200mm/f2.8, you still deal with the same magnification factor in terms of "revealing" the vibration within a system. This may be emphasized by lower mass of the lens, since a lighter setup has less inertial resistance to outside vibration."
Yes, but the question is "Which outside vibration?".
Most large amplitude vibrations in the everyday world are low frequency. If you look at the graph purporting to show that an RRS tripod is much better because it has better vibration damping (http://www.reallyrightstuff.com/tripod-guide) you will see that where the RRS is better is around 100-500Hz, and it is no better below 100Hz (note that the scale is dB, so the same green area lower down the X-axis represents a much smaller effect, so you can ignore the area up at 5-10kHz). The large amplitude vibrations a photographer is likely to encounter, like trucks and trains and herds of wildebeest, are low frequency, in that < 100 Hz range where the RRS is no better. The 100-500Hz range is ordinary music and human speech - middle C on the piano is 260Hz - so if you regularly photograph next to someone with a really loud stereo you might want the RRS, but most of us do not often encounter large amplitude vibrations in that range.
Another point the tripod makers ignore is that vibrations arising in the camera are a different problem to vibrations coming through the ground. The camera generates vibrations when the mirror goes up and when the shutter opens. The camera damps the vibrations arising in the mirror quite effectively, and in some cameras Nikon adds a tiny delay between mirror movement and shutter opening to allow the vibrations to decay, so mirror movement is not a big issue. Vibrations caused by shutter opening cannot be damped by the tripod until they reach the tripod, so the tripod cannot have any effect on the first part of the exposure, and the faster the shutter speed the more of the exposure that is. The speed of sound in aluminium rods is 5000 m/sec, so if you have a 2m tripod it takes the vibrations 0.4msec to get to the bottom, which is not trivial when shutter speed is 1/1000 and the whole exposure lasts 1msec. The damping figures you get in that RRS graph are at equilibrium. That is OK for external vibrations, but not for internal vibrations, where you need to know not how good the damping is at equilibrium but how good it is very quickly.
The tripod can affect vibrations arising in the camera only to the degree that the tripod and the camera are coupled - act as a single mass. If you have a rubber or cork pad between the camera and the tripod, or a poorly fitting quick release, the tripod has much less effect on vibrations arising in the camera.
It is very easy to test whether your tripod is damping internal camera vibrations. Closing the doors on a good car makes a different sound to the doors on a poorly made car: lower pitched, shorter, and with fewer overtones. The reason is that on a good car the parts are tightly assembled. So if you listen to the sound of your camera shutter when it is just sat on a flat hard surface, then clamped on the tripod with the ballhead tightened, you should hear the same difference as with the car doors, and if you hear no difference you have a problem.
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Erik, thanks for your valuable insight.
Thinking out of the box,,, This is quite a stable setup ;D
Your illustrations have shown me some paths out of my box. BTW, I really enjoyed them as well.
Lessons learned:
Seeing a relationship between focal length and weight is specious.
My original question was about a larger hinge circle diameter; you showed an illustration of that. I was probably asking the wrong question.
Any vibration at any magnification is an error that should be minimized if it cannot be eliminated.
Even a common problem may be better served by a unique solution.
I should also reconsider at what point a lens foot is an advantage.
There are more lessons here to be seen later.
Consider if it is possible to leave out parts. For convenience a dovetail system is nice but not always cleaver or absolutely needed.
That is why I am curious about the "one piece apex conversion." Currently the head mounts to a disk with a groove around the periphery. The disk then attaches to the apex by three setscrews. It can be removed to allow a center column conversion. I wanted a one piece when I bought the tripod. Now, for an additional $100, I can have it.
Be aware of how and where you attach all of the elements of a 'tripod'
Camera and or lens
Lens Plate and or rail
Clamp
Head
Tripod top base
Legs, upper and lower
Feet
Ground
All of these parts and interfaces between these are more or less equally important for stiffness and vibrations.
Reading the line above reminds me, "removing the weakest link means the weakest link is somewhere else now."
So knowing a lens with a camera solidly attached is the important part, I ask myself how may it be held to allow best results. I use cameras with fitted AS style plates. I clamp them on a small ball head attached a tripod top base that has already been described. The head is screwed on and then locked with two setscrews from beneath. Improving the connection between the stem of the ball and the QR clamp would require a larger diameter stem.
I will change the feet, but the legs will have to serve for now.
Sam
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Les, I appreciate your input on this topic.
The camera generates vibrations when the mirror goes up and when the shutter opens. The camera damps the vibrations arising in the mirror quite effectively, and in some cameras Nikon adds a tiny delay between mirror movement and shutter opening to allow the vibrations to decay, so mirror movement is not a big issue.
Yes, there is a difference between the sounds and vibrations of cameras I use. Seeing the improvement by using mirror delay prompted some changes. Now it is time to retest and see if there has been progress.
The tripod can affect vibrations arising in the camera only to the degree that the tripod and the camera are coupled - act as a single mass.
That is exactly what I will be working on.
Sam
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Erik,
May I ask what model is your little, stubby Gitzo?
Many thanks on info provided in this thread. Myself.....I'm "breaking in," a new (old) 500mm/4p. It's almost satisfactory on my series 3, Gitzo. (An ancient, giant wingnut model.) I have physical difficulties & the "Wet Arsed" or stool approach, is my best consequence.
A buddy told me to try ("My gosh, I ain't that old") a box of "Depends." Pants get wet, arse stays dry.
The 500p is pretty darned sharp wide open, & getting a pretty good "Wow."
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It's an old series 5 Gitzo about 150 Cm when legs are extended :)
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Thanks Erik,
In error, I purchased a top plate for my aluminum systematic 3. (I didn't realize the 4 & 5's were so huge.) Without starting another thread, I have to ask a question or two.
On my 3 series aluminum, legs extended I rested my cheek on the top section and applied pressure. The legs flexed a bit. I recently purchased a Series 2, CF Gitzo, basically because it was at a bargain price with an Arca, B1 head. (Yes, kinda' top heavy.) Anyway, I did the same cheek, stress test & the smaller CF, didn't flex near the same amount as the larger pod. Which is better?
I am well aware of the advantage of more weight, mass & usability of sturdy legs. In my case, I am only counting my blessings. I had a couple open heart catastrophic, (HeartMate I & II) surgeries. I hate to admit, but I have physical problems. My overall health is good. No machines except a pacer/defib.
I really need a strong pod that weighs nothing with matching bucket to sit on.
8) <humor> :)