Helpful Posts Helpful Posts:  0
Results 1 to 5 of 5

Thread: Focal Length & angle of view

  1. #1

    Focal Length & angle of view

    I am very new to photography and am trying desperately to understand the terminology.

    Could someone explain to me concept of focal length? I have an 18-55 lens and simply cannot get clear on the concept of "the smaller the number, the wider the area the camera sees"...at 18mm my camera sees a wider view than at 55mm..why would a smaller number "see more".shouldn't it more correctly be called focal WIDTH? I think it's the term LENGTH that is throwing me off......

    Anyone who can help me get clear on this will be my saviour!

  2. #2
    PopsPhotos's Avatar
    Join Date
    Sep 2009
    Location
    Washington (state) USA
    Posts
    984
    Real Name
    Pops

    Re: Focal Length

    Focal Length is one of the few numbers in photography which actually works in what we consider "normal" progression. Because it is a measurement of the (effective) distance from the front lens to the film/sensor plane, a longer lens will have a larger number.

    The fact that a longer lens will have a more narrow field of view is not a part of the equation which calculates "focal length." That is an effect of its relationship to the film/sensor area and shape.

    f:stops are backwards because they are fractions and we don't bother with the "one over" part of the term.
    Shutter speeds are backwards because they are fractions and we don't bother with the "one over" part of the term.
    ISO (ASA) numbers are backwards in relation to how much light is needed because that was the way the inventors thought.

    Confused? Welcome to the club.

    Pops

  3. #3
    John C's Avatar
    Join Date
    Mar 2009
    Location
    Atlanta, Georgia
    Posts
    157

    Re: Focal Length

    This site has some excellent tutorials. I suggest visiting the one for focal length and aperture. The link is below.

    http://www.cambridgeincolour.com/tut...era-lenses.htm

  4. #4
    inkista's Avatar
    Join Date
    Nov 2009
    Location
    San Diego, California
    Posts
    1,417
    Real Name
    Kathy Li

    Re: Focal Length


  5. #5

    Join Date
    Dec 2008
    Location
    New Zealand
    Posts
    17,662
    Real Name
    Have a guess :)

    Re: Focal Length

    Get a length of tubing ... Cut 1 length 18mm long, and cut another 55mm long. Look through each one ... Which one has the wider field of view?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •