The Geo Fennel Double Prism Optical Square comprises two pentaprisms of quality optical glass, housed in a sturdy aluminium casing. The housing cover can be rotated to cover the viewing window and protect the prisms when not in use. The prisms are mounted above and below the ‘through’ sighting window, the upper one sighting from the right side, the lower one from the left. The pentaprisms are ground to refract the views by exactly 90°.
Easy to use, simply hold the handle then sight through the yellow lens in the middle to align to a target, then through the clear prisms above and below you can see at right angles to your left and to your right. To get even more accurate there is a slotted hollow handle for attaching a plumbob cord. The extra wide viewing window makes targeting easy. Protective metal cover rotates to expose or protect the prism.
|The Optical Square can be held for viewing in three ways, depending on the needs of the situation.|
|Hand Held without Plumb|
|For a fast estimation of alignment, where exact position is not critical, hold the viewing window to the line of sight, and obtain the alignment required.|
|Hand Held with Plumb|
|By hanging a Plumb bob into the slot on the shaft, an exact position over a point can be maintained for alignment.|
|Set on a Ranging Pole|
|Using the Ranging Pole Adaptor, the Optical Square can be slotted on top of a ranging pole, maintaining a standard height for line of sight, and, using a plumbing level to get a true vertical from the point of alignment.|
|A right angle set with the Optical Square will be true to approximately ±1cm at about 30m.|