Maker

Wild, Heerbrugg, Switzerland

Model

Wild T2 attachment

Serial Number

N/A

Dimensions

Prism diameter 55 mm, Height 100 mm.

Counterweight Length 70 mm, Width 25 mm, Height 55 mm

Image

Description

The rotatable penta-prism, shown above (on the right), is a five-sided prism. It is attached to the objective end of the Wild T2 telescope and is typically used for upward and downward plumbing through shafts of a depth of up to 50 m with an accuracy of about 1:70'000 (when using a theodolite with an altitude bubble). It is used in particular for the difficult task of continuing a traverse azimuth or direction down a narrow mine shaft that may or may not be vertical. This attachment replaces the theodolite with eccentric telescope formerly used for such purpose. Once attached to the objective end of the telescope, the penta-prism gives an accurate right angle (90°) whether precisely attached or not.

The counterweight, shown in the above image on the left, is attached to the eyepiece end, and is used to balance the telescope.

History & comments

The pentagon prism has a cross-section that is symmetrical to one of its "diagonals". It acts like an angle mirror whose mirror surfaces enclose an angle of 45°. It thus deflects the ray by 90° from its original direction, independent from the incident angle on the prism surface.

Conservation

Leather pouch

Condition

Slight visible signs of paint peeling on both the prism and the counterweight

Remarks

• Store no: Fa57
• Catalogued by F. Pall

Dates

Catalogued in 2000.