aperture

Discussion in 'Photography Beginners' Forum' started by gundy74, Jan 3, 2007.

  1. gundy74

    gundy74 TPF Noob!

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    i was just wondering why the aperture on zoom lenses is reduced when zoomed.
     
  2. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    The actual aperture isn't really reduced...but the F number is. The F number is a ratio of the focal length and the diameter of the aperture. So as you increase the focal length but don't increase the size of the aperture...then the F number changes.

    It's a lot more expensive to make and design a lens that allows the aperture to increase in size as it zooms out...so for cheaper lenses...they make the aperture able to open to a certain size...and that's the maximum for both the short end and the long end of the zoom.

    Does that make sense?
     
  3. gundy74

    gundy74 TPF Noob!

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    yes and thank you
     

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