Maximum accuracy and range
The range of a prism results from, among other things, its coating and the glass geometry. A number of Original prisms from Leica Geosystems have a special coating on the reflective surfaces – the Anti-Reflex Coating, and a copper coating on the reverse side. Without these, the range of distance measuring, ATR and Powersearch would be reduced by up to 30%. The workmanship and the durability of the copper coating are decisive for a long life. The glass dimensions, the position in the holder and with it the areal orientation, are important for measuring accuracy.
Leica Geosystems offers a transparent selection of prisms in various sizes for different areas of application. These are standard prisms, special prisms, mini prisms as well as monitoring prisms.
Professional 5000: HIGHEST ACCURACY
Professional 3000: MAXIMUM LIFETIME
Professional 1000: COST EFFECTIVE MEASURING
Measurement errors occur if Original prism holders are not used. Substitutes are not configured according to Leica Geosystems criterion and often exhibit displacement between prism, holder and recording pin. The holder and the prism constitute a unit with which the centring and repeat accuracy is defined. The smallest dimensional change in the geometry of a glass prism or on the holder can lead to a deviation from the centring axis and thereby create measurement errors.
The beam deviation of a prism defines the its maximum range, according to the principle “entering beam should equal the exiting beam”. The smaller the beam deviation (measured in angle seconds), the greater the directly reflected signal strength to the sender optic. The returned signal quality defines the maximum range of a measurement.
In contrast to many conventional prisms, the reflective copper coating on the reverse side of Original prisms consists of a support coating, a vacuum-metallised copper coating, a protective coating and an overlying coat of lacquer. The special adhesive lacquer protects the underlying layers from corrosion and detachment. Working together, the copper coating and the lacquer increase the life of the prism significantly. An additional anti-reflex coating on the sensitive front surface of the prism provides a tough resistance to scratches. The production process of these coatings is so complex that only a very few manufacturers worldwide meet the requirements of Leica original prisms.
Measurement errors occur frequently at close ranges when prisms without anti-reflex coating are used, as the front of a prism always directly reflects a certain percentage of a signal. Errors occur in the use of prisms without copper coating on the back side when moisture droplets accumulate or the prism becomes foggy. Leica Geosystems therefore uses either the stated reflective coating or a patented system for the prevention of fogging and condensation.