Lens question plz help

Discussion in 'Photography Beginners' Forum' started by Raeanne06, Mar 8, 2007.

  1. Raeanne06

    Raeanne06 TPF Noob!

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    I reading a "learn at home" photography book with review questions in the back and there are few that I still can not figure out please help! -Thanks


    1) Does more light strike the film when an fl 1.4 lens is stopped down to fl 11 or when an fl 2.8 lens is stopped down to fl 11?

    2) Does fl 5.6 admit eight times the light of fl 16?

    3) Does a 100mm lens produce an image twice as high and twice as wide as that produced by a 50mm lens?
     
  2. shingfan

    shingfan TPF Noob!

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    1) more light with a small f number.....or large aperture (f/1.4 is larger than f/11)....but f/11 is always f/11

    2) my bad.....f/5.6 is 8 times of f/16......f/4 is 16 times of f/16.....lol :p

    3) no again.....the change would be in the area....not the actual dimension....you would see a little change in height and width when compare a 100mm to a 200mm for the same reason
     
  3. Patrice

    Patrice No longer a newbie, moving up!

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    Assuming the shutter speed stays the same:


    1) Does more light strike the film when an fl 1.4 lens is stopped down to fl 11 or when an fl 2.8 lens is stopped down to fl 11?

    No, f/11 is always f/11


    2) Does fl 5.6 admit eight times the light of fl 16?

    Yes it does, from 16 to 11 is twice as much, from 11 to 8 is again twice as much and from 8 to 5.6 is twice as much again : 2 x 2 x 2 = 8


    3) Does a 100mm lens produce an image twice as high and twice as wide as that produced by a 50mm lens?

    No, the size of the image is governed by the size of your sensor, or negative, and how much enlargement you use when printing or displaying.
     
  4. Christie Photo

    Christie Photo No longer a newbie, moving up!

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    No. f11 is f11 on all lenses.

    Each stop will double or half your exposure, so...
    from 5.6 to 8 = double (2x)
    from 8 to 11 = double again (4x)
    from 11 to 16 = double again (8x)

    Hmmm... I don't really know, but that sounds right. But remember, you will only record the center of that image.

    I hope this helps.

    Pete
     

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