• Great post Neil.

    March 20, 2008
  • Chase

    are we assuming we are at least 10X the focal length away from the object we are imaging? I ask because I see parallel ray. I think it would be an important distinction for macro photography, and also to help me understand a bit better :)

    April 29, 2009
    • For the sake of simplicity in optical diagrams, it is assumed that all rays are parallel, unless otherwise stated. It’s simply to keep things clear for reading the diagrams.

      June 01, 2009
  • Biji Joseph

    Late comment … but isn’t the focal length the distance between the center of the lens and the focal point… in this case the pt where all parallel rays from the object converge after passing thru the lens. the distance of he image from the lens would therefore be greater than the focal length

    April 02, 2012

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