Distance measuring module comprising a variable optical attenuation unit including an lc cell

A surveying apparatus comprising an electronic laser distance measuring module, which comprises an optical transmission channel and an optical reception channel for laser measurement radiation, wherein a variable optical attenuation unit for the laser measurement radiation is provided in the optical transmission channel and/or optical reception channel, wherein:

• the attenuation unit is constructed and designed in such a way that laser measurement radiation impinging on the attenuation unit is attenuated by means of liquid crystals, and for this purpose at least comprises:
• a polarizer comprising a polarization sheet and a single-sided self-adhesive film and adhesively bonded onto a transparent carrier and/or provided with an antireflection layer on one side, or cemented with the transparent carrier,
• a liquid crystal shutter comprising nematic liquid crystals, having a settable variable transmission, and
• a first analyzer comprising a polarization sheet and a single-sided self-adhesive film and adhesively bonded onto a transparent carrier and/or provided with an antireflection layer on one side, or cemented with the transparent carrier.

A method for producing an attenuation unit, the method comprising:

• arranging a liquid crystal shutter between positions provided for a polarizer and a first analyzer, and applying a voltage (U) to the liquid crystal shutter ;
• rotating the liquid crystal shutter about the optical axis of an incident laser beam until an observed laser signal attains a minimum tolerance of ±1° to ±2°;
• connecting the polarizer to the liquid crystal shutter;
• positioning a first analyzer downstream of the liquid crystal shutter;
• and
• rotating the first analyzer about an optical axis of an incident laser beam until an observed laser signal attains a minimum angular tolerance of ±0.1°.