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Old June 1st, 2009, 05:47 AM   #1
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Fluid heads and long lenses - design considerations.

Over the years I have made three fluid heads for different purposes. The first supported an underwater film camera that weighed nearly 40 lbs in air, the second was for a PD 150 and the latest is for a PMW EX3. Of great interest is the ability of the EX3 to use seriously long lenses and this makes head design very demanding. Design can be simplified by making the head side mount, this is because if a side mount head has its tilt axis set at the same point as camera’s centre of gravity there is no need for any counterbalancing springs.

However there are still fundamental decisions to be made, the resistance the user feels when panning and tilting comes from two sources – a static friction component and
a fluid drag component.

An unfortunate property of static friction is that the force required to overcome the friction between two surfaces is greater than that to keep one surface moving over the other. This has the undesirable property of making smooth starts and stops very difficult.

Fluid drag is generated when two surfaces separated by a fluid move past one another, some of the fluid is attached to and moves with one surface, and some is attached to and moves with the other surface. Some of the fluid in between the two surfaces remains stationary i.e. a velocity gradient is set up and this provides resistance to the movement. The resistance increases with the viscosity of the fluid and the magnitude of the velocity gradient. The velocity gradient and drag increases if the thickness of the fluid layer is reduced. The velocity gradient and drag also increases if the pan or tilt rate increases, this is a very desirable property for a tripod head and makes it is easy for the operator to control pan and tilt rates by varying the force applied.

In the case of a long lens there are a couple of problems. A pan rate that is satisfactory for a wide - angle lens is likely to be hopelessly fast for a long telephoto lens. However if the pan rate is reduced to a more appropriate rate the fluid drag becomes very small because of the low velocity gradient. The ability to increase the velocity gradient by making the fluid layer thinner is limited by play in the bearings and manufacturing tolerance considerations. Increasing the fluid viscosity is another possibility but I have never been able to obtain higher than 600,000 centipoise Viscasil.

At low pan rates then there is little fluid drag and as a result the static drag becomes more important. Starts and stops become more abrupt. The problem can be alleviated to some extent by the rubber band pulling the panhandle trick. The energy stored in the stretched rubber band provides a more constant force on the panhandle than if the handle is gripped directly.

The static friction can be reduced by the use of good bearings and low friction seals. If this is done it is possible to pan and tilt at longer focal lengths and achieve smooth stops and starts. However the system becomes very delicate and very precise leveling is required to stop the head panning to its lowest point on its own. The accuracy of leveling required is greater than that readily achievable by a circular level and a ball-leveling tripod. It is certainly much more demanding than any one would choose to persist with in the field. Adding static friction brings back the sudden stops and starts. I am yet to decide on how much or how little static friction is a good compromise.

Although I have not finished my experiments I expect that I will end up with a system where I can pan using 300 mm lenses with some success and possibly longer lenses under ideal conditions. However I still have a couple of possibilities to think about and explore.

Does anyone have anyone have any solutions or ideas to try?
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Old June 1st, 2009, 08:03 AM   #2
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The Ronford F7 is one of the best heads I've used for fine work. Perhaps not the head to carry large distances because of the size and weight, but it's very responsive.
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Old June 1st, 2009, 01:14 PM   #3
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Thanks for that technical description Alastair. I've been through just about every head on the market in the hunt for the best one for long lens work. I've owned Sachtler 18II, 20II, 25II, 25 Plus, Studio II, Ronford 2003, 2004, Atlas 30, O'Connor 1030, and now the 2060HD which is my current head of choice.
But, I think that the issue you're talking about, the conflict between friction and fluidity is one that can never be "perfect" and we're always going to have to compromise.
But if you do ever come up with a solution, I for one would be interested!
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Old June 3rd, 2009, 10:17 PM   #4
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Hi Alastair...........

Fascinating insight to head design and building.

What seems to stand out from your excellent article is that a purely mechanical solution to the problems thrown up may not be possible, at least not without involving "Defence Department" type budgets and resources.

Perhaps the time has come to think laterally and look at some type of electronic/ computer servo control that can have the required parameters programmed in to mimmick the operations curve required.

In short, remove the hand on the pan bar and replace it with "fly by wire".

As you may be aware, such systems are capable of almost infinately fine positioning and movement, start up and stop characteristics can be developed removing those undesired characteristics you mentioned and all sorts of other great stuff.

Bit like one of these little beauties:

Vinten | Vector 950 Active Pan and Tilt Head | www.vinten.com

Shame they don't do one for a bit further down the food chain............

Pre Script: Late breaking news, just in from the web:


A few minor alterations and this could just be the next best thing to hit the camera support market. Just needs a "Major Player" to step up and see the possibilities. Coupled with "target reckognition" (like face, just doesn't need the face!) and a few other whizz bang bits and pieces, it could see the common tripod/ head combination consigned to the dustbin of history.


Last edited by Chris Soucy; June 3rd, 2009 at 11:32 PM. Reason: +
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Old June 4th, 2009, 07:25 PM   #5
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Hi Brian, Steve and Chris,

Thanks for your comments and information. As far as I am concerned the very heavy and very expensive heads are out of the question, although I can see the advantages of increasing the size and mass.

Chris you may also be interested in the SFH-30 Stopframe & Timelapse Motion Control head and other fascinating devices at Motion Control Rigs, Cameras, Heads, Platforms, Pan Tilt Heads, Cranes and home of Milo

To complete my current project I have been experimenting further with flexible panhandles and have found that if there is about 3” (70-80 mm) of deflection before the head moves I can achieve a steady pan rate of about 0.05 degree /sec. This is in windless conditions and represents a pan time of 30 seconds across the EX3 finder field with a 300 mm lens.

This post has triggered a couple of lateral thoughts of my own and even though my current project has produced a 1 kg head that is useable with a focal length of 300 mm on an EX3 I can feel another head project coming on.
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