The Oberwerk 45° 25x100mm was originally designed to be 25x only, but Oberwerk now has custom 40x EP's that work very well with this model. Changing the eyepieces is relatively simple, but not as easy as other models that were designed from the start with chageable eyepieces, such as the 100mm Binocular Telescope. The eyepieces in the 45° model are threaded, and screw into the prism covers. In order to prevent the eyepiece from unscrewing while adjusting focus, there is a setscrew that secures each eyepiece in the prism cover. The photo at right shows the location of the setscrews. To access the setscrew with a small screwdriver, adjust the inter-pupil distance to the widest setting. The rotation of the prism housing puts the setscrew in a position that is reachable with a screwdriver. Carefully loosen the setscrew, but do not remove it (as it is very tiny and easily lost). Stop loosening the setscrew when it protrudes from the prism cover by 1/16". Now the eyepiece can be unscrewed and removed from the prism cover. Carefully screw in the 40x eyepiece, being careful not to cross-thread. Once the 40x eyepiece is fully screwed in, tighten the setscrew, but be careful not to over-tighten (tighten only enough to prevent the eyepiece from unscrewing when focusing).
Repeat for the other side.
Note that the close-focus distance for the 40x eyepieces is much longer than the standard 25x eyepieces, in fact, it will not be possible to focus closer than 200 yards with the 40x eyepieces.
If you have any trouble with the above procedure, please contact Oberwerk technical support at support@oberwerk.com.
