Why Do the Basler Lenses Have an Orange Dot for F-Stop 2.8 Value#
Closing the lens aperture (turning the aperture ring to a higher f-number) increases the diffraction blur.
On the other hand, the aberrations are less with higher f-numbers where the peripheral rays are excluded.
With most lenses, the sum of diffraction blur and aberrations drops with higher f-number, but will rise again with further f-number increase.
The resulting minimum of blur, hence the maximum of resolution, is found with Basler lenses at an f-number value of 2.8.
This is the critical aperture and marked by an orange dot on the aperture scale.
