Depth of Field with Long Lens

Discussion in 'Beyond the Basics' started by billybudd, Feb 28, 2005.

  1. billybudd

    billybudd TPF Noob!

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    From the 25th floor, I shot aperture priority with a Nikon d-70, 80-200mm lens, a tall steeple 2 blocks away at 80mm focal length and 2.8 aperture. I am stunned at the depth of field. Buildings 10 blocks away are in excellent focus. When shooting at 2.8 aperture I am accustomed to no depth of field. What's going on? Thanks for the feedback, DV
     
  2. Big Mike

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

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    Welcome to the forum.

    My guess is...at that distance, you are already at infinity focus so everything past a certain distance will be in focus. To blur the background with a short DOF, you would have to get closer.
     
  3. SLOShooter

    SLOShooter TPF Noob!

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    Three factors go into DOF. Aperature, focal length, and distance to subject. As the mentioned above your at infinity so your not going to get a thin DOF.
     
  4. DocFrankenstein

    DocFrankenstein Clinically Insane?

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    Actually, it's 2 factors:

    Physical size of the aperture and the distance to the subject.
     
  5. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    For most 35mm lenses anything beyond 35' or 40' is going to be at "infinity". 2 city blocks is going to be well past infinity for almost any lens.

    I'll second that there are 3 factors that go into DOF: aperture, focal length, and focus distance, but no matter what your f/stop and focal length if you include infinity in the DOF, then everything past what you are focusing on will be in focus (not considering atmospheric effects).
     
  6. Christie Photo

    Christie Photo No longer a newbie, moving up!

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    You can get a good sense of this by reading the scale on your lense barrel. It's a bit tougher to understand with a zoom lens. Take a look at a fixed focal legnth lens.

    And yeah... I gotta agree, the longer the lens, the shallower the DOF.

    Hope this helps.

    -Pete Christie
     
  7. billybudd

    billybudd TPF Noob!

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    Thank you for your thoughtful posts---I understand. DV
     

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