Wayne,
you beat me by 20 minutes .... it is not a rangefinder.
I also have been checking on that and YES, it is a Scherenfernrohr (scissors telescope)  
More information here ....
http://www.panzeraufgd.co.uk/optics.html
This hybrid between binoculars and a periscope enabled the observer to  remain safely concealed in dug outs, behind walls or even tree trunks  with only the objective lens visible to the enemy. 1905 saw the design  refined further with an army-issue variant and a field artillery model  being trialed and adopted. Naturally other countries produced their own  versions of the scissors telescope and when World War I broke out both  opposing armies all along the Western Front observed each other from  their trenches using such equipment. By World War II the design remained  virtually unchanged except for an upgrade in magnification to 10 x 50  and continued to be a useful tool in the Wehrmacht for general  observation (in both vehicles and on the ground) and for artillery fire  observation and direction throughout the war.
John