Gehmann #344K 23mm Centering device for Shooting glasses-

Attaches to the lense holder on your shooting glasses.
*Not suitable for ordinary glasses

The centring device is put in front of the lens or the open iris shutter for precise adjustment of the lenses. The lens then has the optimal adjustment i.e. precisely centred as soon as the sight picture shows a perfectly round target bull. After centring the device is taken off again.

This 344k can be also used as colored filter holder when the conical device is removed.