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How to Choose a Tripod

tripods

Transits and theodolites get more attention than that humble but crucial three-legged stabilizer called a tripod. Not all tripods are created alike, so it’s important to know which kind is best suited for the job. 

Tripod Stress Tests

High-quality tripods are performance tested to determine how they will affect the instruments you attach to them.

  • Horizontal drift is a measure of how a tripod’s orientation changes over time, especially under the load of an instrument like a theodolite. After enough time, that change can affect the instrument’s accuracy. All tripods are subject to horizontal drift after a few hours – some more than others.
  • Height stability measures the amount of vertical deformation a tripod exhibits under a working load. Heavy-duty tripods are for use with up to 30 kilograms (65 lbs.) of weight, while light-duty tripods are meant to hold no more than 10 kilograms (22 lbs.). While TPS angular accuracy isn’t really affected by vertical deformation of up to 5/100ths of an inch, precision leveling applications require extreme height stability. The taller your tripod, the less stable it becomes.
  • Torsional rigidity is a measure of the tripod head plate’s horizontal rotation. A related measure, hysteresis, describes how well the tripod head returns to its original position after rotation. Lighter tripods lose torsional rigidity over time, which will affect your instrument’s accuracy, as well.

Not all tripods are suited for all applications. Knowing whether you’ll need to set up for long periods of time, work in windy or humid conditions, or negotiate a range of ground surfaces will affect your decision.

Materials Matter

Depending on the material a particular tripod is made of, it may or may not be appropriate for the job you have in mind.

  • Wood (beech or pine) is the most stable tripod material, with only 1 to 2 inches of horizontal drift over 3 hours. Wooden tripods are best suited for TPS applications, GPS antennas, prism targets, and other long-term setups.
  • Fiberglass is a heavy-duty alternative to wood, but is subject to greater height stability and hysteresis errors. Horizontal drift after 3 hours can be as much as 5 inches.
  • Aluminum is the lightest and least expensive material, and offers height stability, but it is susceptible to horizontal drift of between 3 and 8 inches over 3 hours. This means aluminum tripods are not good for angular measuring but are well suited to leveling jobs. Let an aluminum tripod sit for 20 minutes before you start taking measurements, and check its orientation frequently during use.

Keep In Mind…

Factors like humidity, wind speed, setup time, temperature, ground type, and interaction with the tribrach all affect your tripod’s performance. Be sure to choose the right tripod for the job, and you’ll set a solid foundation for accurate measurements.

Need help choosing the right tripod? Contact us for expert guidance from our knowledgeable staff.