Spotting scope DDoptics Pirschler HDX 15-45x60 G - straight view 
Influence of objective lens diameter on the light intensity of the binoculars or on the objective lens light intensity The "second" figure (e.g. ..x50) indicates the diameter of the front lens of the objective lens (usually the larger diameter) in mm. The larger this is, the more light can be absorbed by the lens of the optical system. While a lens diameter of 20mm is sufficient during the day [...]
