When "5" is selected: 50mm bright frame line is appeared in the viewfinder.
When "8.5" is selected: 85mm bright frame line is appeared inside besides 50mm line.
When "10.5" is selected: 105mm bright frame line is appeared inside besides 50mm & 85mm line.
When "13.5" is selected: All the line is appeared.
The color of each frame line matches with the one of the number on the selector.

*Parallax is automatically corrected regardless of focal length.