The role of prism

Prismatic degree refers to the deviation of light after passing through a specific point on the lens. Prism degree is expressed in centimeters per meter (cm/m), the unit name is "prism diopter" and the symbol is "△".

Prism is a polyhedron made of transparent materials (such as glass and crystal). It is widely used in optical instruments. Prisms can be divided into several types according to their properties and uses.

For example, in spectral instruments, the "dispersion prism" that decomposes composite light into spectra is an equilateral prism; In periscope, binoculars and other instruments, right-angle prism is generally used to change the direction of light and adjust its imaging position.

Extended data:

1, prism constant measurement method

There are two methods to determine the prism constant of total station ranging, namely "six-segment method" and "three-station method". This paper briefly introduces the "three-station method":

(1) Choose three points A, B and C on the same straight line on the relatively flat ground, and point B is roughly the midpoint of AC.

(2) Set up a station at point A, and measure the horizontal distance between two groups of AC, with each group reading five times, and the average value of the two groups is Dac.

(3) Set up a station at point C, and measure the horizontal distance between two groups of CAs. Each group reads five times, and the average value of the two groups is Dca.

(4) Set up a station at point B, and measure the horizontal distance between BC and BA in two groups, with each group reading five times, with the average values of Dbc and d BA respectively.

(5) Prism constant△ = (DBA+DBC-(DAC+DCA)/2).

(6) The additional constant of prism is c =-△.

(7) If the original prism constant of Leica is 34.4mm set in Leica total station, then this prism constant is set to C .. But the prism constant of this prism itself is: (C-34.4) mm..

The extra time it takes for the "prism constant" light to propagate in the reflective prism will increase the measured distance by a certain value, that is, the propagation speed of light in glass is slower than that in air. Usually, we call this increased value the prism constant.

Usually, the prism constant has been marked in the manual attached to the manufacturer or on the prism used for ranging. When it is used in a reflection prism that is not matched with the total station, the prism constant must be determined first.

2. Preventive measures

(1) The prism of our common centering rod can be installed back and forth. Even if the same centering rod is used in different installation positions, the prism constant is different.

(2) Before the total station is used in field work, its prism constant should be determined first.

Baidu encyclopedia-prism

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