tripod

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Young George Washington using a surveyor's tripod

Tripod is a word generally used to refer to a three-legged object, generally one used as a platform of some sort, and comes from the Greek tripous, meaning "three feet". A tripod provides stability along the side-to-side and up-and-down Coordinate axis of motion and provides a large amount of leverage. Tripods have the disadvantage of being heavy and bulky although when it can be used with large equipment.

Firearms

Seabees train with the M240B mounted on a tripod.

A tripod used to support a rooftop television antenna

On firearms, tripods are commonly used on machine guns to provide a forward rest and to reduce motion from recoil. Machine guns are capable of firing long continuous bursts of fire, but at the cost of increased recoil (which decreases accuracy), and increased weight (machine guns are heavier in order to absorb the stresses of prolonged fully-automatic fire). The tripod permits the operator to rest the weapon on the ground and thus the gun feels lighter to the shooter and accuracy is increased.

Photography

Usage

Tripods are used for both still and motion photography to prevent camera movement. They are necessary when slow-speed exposures are being made, or when telephoto lenses are used, as any camera movement while the shutter is open will produce a blurred image. In the same vein, they reduce camera shake, and thus are instrumental in achieving maximum sharpness. A tripod is also helpful in achieving precise framing of the image, or when more than one image is being made of the same scene, for example when bracketing the exposure. Use of a tripod may also allow for a more thoughtful approach to photography. For all of these reasons a tripod of some sort is often necessary for professional photography as well as certain video uses.

Construction

For maximum strength and stability, most photographic tripods are braced around a center post, with collapsible telescoping legs and a telescoping section at the top that can be raised or lowered. At the top of the tripod is the head, which includes the camera mount (usually a detachable plate with a thumbscrew to hold onto the camera), several joints to allow the camera to pan and tilt, and usually a handle to allow the operator to do so without jostling the camera. Some tripods also feature integrated remote controls to control a camcorder or camera, though these are usually proprietary to the company that built the camera.

Surveying

A surveyor's tripod is a device used to support any one of a number of surveying instruments, such as theodolites, total stations, levels or transits.

Usage

The tripod is placed in the location where it is needed. The surveyor will press down on the legs' platforms to securely anchor the legs in soil or to force the feet to a low position on uneven, pock-marked pavement. Leg lengths are adjusted to bring the tripod head to a convenient height and make it roughly level.

Once the tripod is positioned and secure, the instrument is placed on the head. The mounting screw is pushed up under the instrument to engage the instrument's base and screwed tight when the instrument is in the correct position. The flat surface of the tripod head is called the foot plate and is used to support the adjustable feet of the instrument.

Positioning the tripod and instrument precisely over an indicated mark on the ground or benchmark requires techniques that are beyond the scope of this article.

Construction

Many modern tripods are constructed of aluminum, though wood is still used for legs. The feet are either aluminum tipped with a steel point or steel. The mounting screw is often brass or brass and plastic. The mounting screw is hollow to allow the optical plumb to be viewed through the screw. The top is typically threaded with a 5/8" x 11 tpi screw thread. The mounting screw is held to the underside of the tripod head by a movable arm. This permits the screw to be moved anywhere within the head's opening. The legs are attached to the head with adjustable screws that are usually kept tight enough to allow the legs to be moved with a bit of resistance. The legs are two part, with the lower part capable of telescoping to adjust the length of the leg to suit the terrain. Aluminum or steel slip joints with a tightening screw are at the bottom of the upper leg to hold the bottom part in place and fix the length. A shoulder strap is often affixed to the tripod to allow for ease of carrying the equipment over areas to be surveyed.

Astronomy

The astronomical tripod is a sturdy three-leg stand used to support telescopes or binoculars, though they may also be used to support attached cameras or ancillary equipment. The astronomical tripod is normally fitted with an altazimuth or equatorial mount to assist in tracking celestial bodies.^[1][2]

References

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