Fluid head explanation?

[Hans Henrik Bang]

Sorry about this "newbie" question but am new to the world of tripods.

What exactly is a "fluid head" and how does it work? I have rummaged around in this forum and have gotten the point that a fluid head will allow you to do smooth pans and tilts from standstill. Something my current cheapo tripod will not do. There is an inevitable jerk when force applied overcomes static friction.

I just want to know what is behind the word "fluid head". Is is just a term for a good enough head, or is it some specific technology that I will be able to spot?

Hope someone can point me to an explanation. I am an engineer, so cursed by an overwhelming desire to know how things work :-)

Hans Henrik

[Charles Papert]

Hans:

A fluid head literally uses fluid, i.e. viscous oil between the mechanical components that allow the smoothest movement. A quality fluid head will allow for the subtlest of movement with clean starts and stops, as well as jerk-free pans. They are not cheap, but are an absolute must for anyone who is looking to deliver work that is beyond home movies.

While looking at manufacturer's websites (Sachtler, O'Connor, Miller are a few of those that offer them) you will see the term applied when appropriate.

There are also "fluid effect" heads that are a notch down, using a lower grade lubricant to simulate the effect to a lesser degree.

Friction heads are usually meant for still photography where moves are not critical. If a head offers the ability to tilt 90 degrees to the side, chances are it is not intended for film/video use, rather it allows still photographers to compose in the vertical format.

[Frank Granovski]

If it doesn't say, "fluid head," it is a friction head, using nylon washers. My Manfrotto 136 head is a friction head. Works great, though, but it is not as smooth as a Miller DS5.

[Hans Henrik Bang]

Thanks Charles and Frank.

Just the explanation I was looking for.

Hans Henrik

[Jeff Donald]

Frank is correct about the fluid head etc. But what you have to watch out for is less scrupulous manufactures and distributors labeling their heads fluid head effect. People see fluid head in the brochure and ignore the effect. What they get is a low end, friction head, hence the fluid head effect

[Mike Rehmus]

As far as I can tell, not having taken my Miller head apart, I think a true fluid head is basically a pump that moves silicon fluid through an adjustable orifice to control the movement. The pump system provides the best control and the silicon as a working fluid gives it the all-temperature performance.

The others may have two washers facing each other with a silicon fluid between them if one is lucky.

But what do I know?

Anyone actually seen a drawing or taken a good head apart?

[Jeff Donald]

O'Connor used to have a diagram of a fluid head on their site, you might look their.

[John Beale]

As far as I know my O'Connor #30 is a true "fluid head", at least the label says so. It is pretty old, I don't know how old. There are no pumps or any fancy mechanisms. The fluid drag is adjusted by the spacing of a collar around a shaft which is packed in a very stiff (near-solid) grease. Here are some photos of the head partly disassembled: http://www.bealecorner.com/D30/070417/index.htm

[David Garvin]

Originally Posted by Mike Rehmus

I think a true fluid head is basically a pump that moves silicon fluid through an adjustable orifice to control the movement. The pump system provides the best control and the silicon as a working fluid gives it the all-temperature performance.

I used to have a set of wooden sticks with a fluid head and I'm with Beale, there were no fancy pumps or anything like that. I will say that there was a sticky oily liquid that would slowly leak out over the years that I would guess was not "silicon fluid".

[Tim Le]

Thanks for the photos John. The Model 30B is a pretty old head so it's probably not a good example of modern fluid head design. OConnor's modern heads (90's and on) were totally redesigned and they use a different type of drag adjustment mechanism which consist of several groups of "sectors" that are controlled by a linkage. The principles are still the same--you're shearing viscous fluid--but the mechanism is more complicated than what you see there. The counterbalance is also completely different in the modern heads because it is designed to account for the non-linear torque curve of a tilting head.

By the way, did you know Chadwell O'Connor used printer's grease as the fluid when he made his first fluid head in 1949? But then he found it got too thick at low temperatures and too thin at high temperatures. By 1952, he settled on a silicone based compound. Not sure what they're using now but it's probably still silicone based.

[John Beale]

I haven't done a chemical analysis on the fluid in my old #30 head but I was guessing polydimethylsiloxane or something very similar to it. This material is sold by Dow Corning in a wide range of viscosities. In the #30 head, I estimate the viscosity to be around 100,000 cts, which to put it in familiar terms falls somewhere between molasses and peanut butter in resistance to flow.

Here's the product I believe is very similar to the #30 head fluid:
http://www.dowcorning.com/applicatio...lt.aspx?R=87EN

[John Beale]

Originally Posted by Tim Le

The counterbalance is also completely different in the modern heads because it is designed to account for the non-linear torque curve of a tilting head.

Thanks for the O'Connor info, I didn't know that! By the way the #30 head counterbalance uses an offset linkage to the tilt arm to drive a plate that compresses a set of springs. This generates a restoring force that is sinusoidal with increasing tilt angle. The torque due to the camera weight above the head is also sinusoidal with tilt angle. However, the gravity torque peaks at 90 degree tilt and the #30 spring counterbalance peaks at 180 degree tilt. You could get precisely correct restoring force (neglecting any friction) by adding a 2:1 gear. Never having seen inside a modern O'Connor head, I don't know if that's what they do.