+1 on above. I use my comparable 28/2 for many things, but not for headshots, not of people with whom I want to stay on good terms. The conventional wisdom here is roughly:
* 20mm for context
* 30mm for full-body
* 40mm for 3/4 body
* 50mm for 1/2 body
* 70mm for head+shoulders
* 80mm for loose headshots
* 100mm for tight headshots
An 18-135 or 18-250 will make this breakdown quite clear to you: test various focal lengths and distances, see what works for you and your subjects.
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As for those blurry backgrounds you want: DOF is photographically controlled by aperture, focal length, and camera-subject distance. Here are the rules again:
* For thinner DOF, use a wider aperture and/or longer focal length and/or closer distance
* For thicker DOF, use a tighter aperture and/or shorter focal length and/or further distance
But subject isolation is also affected by lighting and subject-background distance. A well-lit subject stands out from a darker or bland or moving background (BG). A further BG is blurrier than a closer BG. A fast short lens won't produce the effect you want if camera-subject distance is too far, the subject-BG distance is too close, the subject isn't lit, the BG is too bright or busy. ALL THESE OTHER FACTORS MATTER MORE THAN THE LENS! My Kodak guidebook to portraiture barely mentions lenses, instead emphasizing lighting, poses, clothes, makeup, but especially lighting.
My favorite head+shoulders and headshot setup, whether with APS-C or 135/FF or 120/MF cameras, is about 80/3.5 shot from 1.5-2m with an indistinct BG about 2-3x further away. IMHO this gives the best modeling|rounding of human features, and best minimalization of BG. I now use a 75/3.5 enlarger lens (under US$10) on extension for sharp headshots.
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Note on headshot lenses: The AOV differences of headshot focal lengths are trivial. The angles on my K20D are like this:
70mm 23 degrees
75mm 21 "
80mm 20 "
85mm 19 "
90mm 18 "
In other words, any decent lens in that range will give a similar view. The trick is in knowing how to use it, eh?
Last edited by RioRico; 03-31-2012 at 06:11 PM.