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DPChallenge Forums >> Photography Discussion >> DOF and Zoom lens?
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 12/29/2006 01:42:53 PM · #1
I was wondering if dof changes at all with a zoom lens that has a fixed aperture.

For example, say I have a 50-150mm F/2.8 lens (dreaming yet) and you take two photos.

One photo at 50mm f/2.8 and one at 150mm f/2.8
Will the dof change at all?

12/29/2006 01:45:09 PM · #2
Oh yes, the shot at 150mm will have considerably less DOF.
 12/29/2006 01:45:49 PM · #3
Oh and you know a lot of 70-200 2.8 lenses exist so that´s pretty close to your imaginary 50-150mm :)
 12/29/2006 01:48:40 PM · #4
Originally posted by Larus:
Oh and you know a lot of 70-200 2.8 lenses exist so that´s pretty close to your imaginary 50-150mm :)


Yeah, knew that. Dreaming as in I don't have the cash for one right now, lol. :)
 12/29/2006 01:49:06 PM · #5
Yup, all the rules still apply. :-)

Online Depth of Field Calculator
 12/29/2006 01:49:14 PM · #6
Originally posted by Larus:
Oh yes, the shot at 150mm will have considerably less DOF.


Thats great to know, thanks!
 12/29/2006 01:50:15 PM · #7
Originally posted by dwterry:
Yup, all the rules still apply. :-)

Online Depth of Field Calculator


Wow, thats really cool..
 12/29/2006 01:50:23 PM · #8
Depth of field is relative to the ACTUAL physical size of the aperture. As your zoom is zoomed, even though the f-stop stays the same, the physical size of the aperture changes. (f-stop is a ratio of aperture size to focal length.) Thus, as the aperture get larger, depth of field will decrease, regardless of the aperture ratio.

This is one reason that cheap zooms don't do as well for long distance portraits as the good ones. The aperture is not as large, even though the focal length is the same.
 12/29/2006 01:52:33 PM · #9
Originally posted by dwterry:
Yup, all the rules still apply. :-)

Online Depth of Field Calculator


Also answers my question I had about subject distance.

Awesome calculator, thanks..
 12/29/2006 01:54:12 PM · #10
Originally posted by nards656:
Depth of field is relative to the ACTUAL physical size of the aperture. As your zoom is zoomed, even though the f-stop stays the same, the physical size of the aperture changes. (f-stop is a ratio of aperture size to focal length.) Thus, as the aperture get larger, depth of field will decrease, regardless of the aperture ratio.

This is one reason that cheap zooms don't do as well for long distance portraits as the good ones. The aperture is not as large, even though the focal length is the same.


Very intersting, another reason to keep saving for the faster zoom. :)
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