It's difficult to find a good prism, because the important role for prism is reflection. Of course, you can check the appearance such as dirt or damages. But it does not say good appearance is good prism. To check the following points, you can recognize what the good prism is.
1. Angular beam deviation
Angular beam deviation is the angle made by incoming & outgoing beams. If the angle is 0 or near to 0 degree, possible to survey more accurate.
Good Deviation
Bad Deviation
"Measurement value"
The distance is determined by emitting and receiving multiple frequencies, and determining the integer number of wavelengths to the target for each frequency. Unless reflected beams go straight back to instrument, the measurement value is not accurate.
"In case of bad deviation prism"
Shorter Measuring Distance
*can not use long distance
Making Value Error
*longer than correct value
2. Prism coating
Why does prism need coating? It's because coating prevent scratching, fogging, and keep the degree of reflection. Myzox prisms have been coated by silver/copper, these degree of reflections are higher than other materials. Please check the following graph.
Beam Deviation & Prism Costing of Myzox Prism series
