Have scopes nowadays Porro or Roof prisms? (1 Viewer)

[richard866945]

Hi,

the moniker fast focal ratio (focal length divided by objective aperture - or the other way round) comes from photography, were a fast focal ratio (smaller number or larger fraction) means shorter or faster exposure times are possible.

Fast lenses are tricky to make well and even very small defects have grave effects.

Joachim

Thank you and it shows that we are never too old to learn.
Richard