• Please use real names.

    Greetings to all who have registered to OPF and those guests taking a look around. Please use real names. Registrations with fictitious names will not be processed. REAL NAMES ONLY will be processed

    Firstname Lastname

    Register

    We are a courteous and supportive community. No need to hide behind an alia. If you have a genuine need for privacy/secrecy then let me know!
  • Welcome to the new site. Here's a thread about the update where you can post your feedback, ask questions or spot those nasty bugs!

f-number

  1. Doug Kerr

    Why the f-number matters in exposure

    One may wonder why the measure of the "taking aperture" we know as the f-number (the ratio of the focal length of the lens to the diameter of the aperture) is seen as one of the pivotal parameters of exposure. It might seem that the diameter of the aperture itself (or perhaps its area) would be...
Top