• BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

    Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Search results

  1. jmepler

    Please school me on the Pentax 65

    To calculate magnification, divide the focal length of the scope by the focal length of the eye piece. Conversely, to solve for eye piece focal length, divide the scope focal length by the desired magnification. The focal length of the PF-65ED is 390mm. So, for 20X take 390mm/20x = 19.5mm eye...