Mechanically mounting a camera to a support device and controlling over pointing seems like a relatively easy task. The camera needs to be securely fastened, and the support needs to be stable with the weight applied. But as with all things, this concept becomes more complicated when the details are considered. Today, modern technology and thoughtful engineering have considerably advanced camera support.
Friction
A tripod and pan head work together to allow the camera operator to accurately point the lens at a scene while facilitating smooth movement. Zero friction would create a disaster. The lack of human muscle control would cause unstable operation, particularly when wind or other factors add mechanical loads to the assembled mechanical system. Instead, a degree of controlled friction must be applied if physics and physiology are to cooperate successfully.
This friction is accomplished in the pan head. Camera support systems must be designed so that the center of gravity of the camera is allowed to maintain the appearance of perfect balance at all tilt angles.
In a post head, the camera's center of gravity is placed precisely on the center of rotation of the tilt mechanism. By doing this, as the camera tilts, gravity acts precisely the same at all angles, allowing the camera to remain stable in any position. Further, the force that must be applied to move the camera is consistent at all times.
Post heads were once quite popular for production use. However, they tend to be large and expensive. Today, they are commonly used in robotics.
Springs for balance
Other approaches to the issue of tilt over center are equally effective. Adding springs to the tilt mechanism can provide resistance that is proportional to the angle. In effect, this creates a balancing force that precisely compensates for the force of gravity.
This approach has been used for decades to allow pan heads to adapt to cameras of varying sizes by adjusting the spring tension.
In the most modern designs, the tilt and pan have an adjustable friction, which is often modified by a viscous fluid acting on the axis of rotation. This creates a smooth action, which has an adjustable resistance. In some sophisticated pan heads, the amount of friction and the balancing force are shown in a digital readout, so setting a pan head for a specific camera is much easier. By combining the springs with a camera mechanism, the counterbalance can be much more accurate and progressive in action, a feature common in high-end pan heads for large and heavy field/studio cameras.
Choosing the right combination
Technology does not completely overcome physics. Large and heavy cameras often cannot be balanced at all tilt angles. Review the specifics of the intended application to ensure that the pan head chosen will adequately accommodate the combination of lens and camera.
Most manufacturers can provide charts that assist in evaluating the suitability of the pan head to the chosen camera/lens combination. However, these charts are often hard to obtain, so it's a good idea to talk with a technical representative from the support equipment manufacturer to make sure suitable choices are made.
Figure 1 shows the ability of one pan head to accommodate full tilt range only with certain combinations of total weight and height of the center of gravity.
Choose a pan head that is intended for the weight range. Again, Figure 1 shows that lightweight cameras are not suitable. With the advent of lightweight consumer crossover cameras, such as HDV camcorders, choose much lighter duty pan heads to ensure a good match between camera size, weight and the pan head.
Structure
The structure under the pan head is another important element of camera support. The studio pedestals of the 1950s were often nearly the weight of the camera. Lead weights on complicated pulleys provided counterbalancing to the camera mass. This of course meant that the camera/pedestal combination weighed about half a ton. One time while I was taping, the cables on my camera/pedestal combination snapped.
As cameras got smaller and lighter, air balancing was introduced. This incredibly smooth process allowed for a wide range of weights. Air-balanced systems are still the Mercedes of the industry, with costs to match. Some manufacturers offer up to four-stage lift columns, along with models that can be folded up for field use.
Field tripods must be extremely strong and light enough to be carried. The high end of the camera weight scale includes heavy steel or aluminum tripods suitable for heavy-duty use. Modern material science has provided more lightweight options, including alloys and carbon fiber, which provide the strength of steel without the mass. Carbon fiber, though light, strong and durable, is expensive. Like pan heads, tripods must be chosen for the weight range of the intended camera.
Finally, make sure the pan head and tripod have the correct mating surface. Heavy-duty tripods for field cameras often have a Mitchell Mount, which is a carryover from cinematography. (See Figure 2.) Usually the mounting is a bowl that allows the pan head to be leveled independently from the tripod. Bowl sizes range from 75mm to 150mm, requiring careful planning for the complete system.
Lastly, it is valuable to note that the group Vitec Group in the UK owns several of the manufacturers of both tripods and pan heads. There are many products available that cross brand boundaries, giving you the freedom to choose the brand you prefer and still get the product you desire.
John Luff is a television technology consultant.
Send questions and comments to:john.luff@penton.com
