Udda prismasökare för att se det som är 90° vid sidan om du tittar rakt fram. Nåt militärt antar jag. Glasen OK.

Kommer i fin ask, distribuerad av Preisler Malmö (!). 7 cm lång är prylen. Grön krackelerad lack med lite spår av bruk på. Se bilder.

Mer info:

A double pentagonal prism also known as a (double) angle prism) is a simple but important optical instrument in geodesy for staking out or checking right angles, angling a point onto a straight line (i.e. the plumb from the point onto it to fall straight) and to line yourself up in a straight line.Angle prisms are available in different designs. The most common are the double pentagon prism and the cross sight. The double pentagon prism, also double pentagon or double pentaprism, is the easiest to handle. Two pentagonal glass prisms are placed one above the other in the double pentagon prism. The angle prisms have a hole or notch at the lower end of the handle into which a plumb line can be inserted. The surveying-relevant location of the angle prism (perpendicularly below the angle prism on the ground) can thus be easily determined.

A prism is a translucent glass body whose (flat) boundary surfaces are ground and sometimes also mirrored. A prism is used to deflect light rays by reflecting or refracting light.

Beam path in the double pentagon

The double pentagon prism has two opposite prism mirrors and a transparent window through which all three can be sighted at the same time. If you are roughly on the straight line between two range poles, you can observe the left pole in one prism mirror and the right pole in the other prism mirror. When both images coincide, the angle prism is exactly in the connecting line. If a third rod is seen in the viewing window in such a way that it also coincides with the other two rods, then it is exactly perpendicular to the line of flight whose base is in the prism