Depth of Field with Long Lens

[billybudd]

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

 

[Big Mike]

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.

 

[SLOShooter]

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.

 

[DocFrankenstein]

Actually, it's 2 factors:

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

 

[ksmattfish]

... 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?

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).

 

[Christie Photo]

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

 

[billybudd]

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