BG blur / subject isolation with different lenses/crop?

Discussion in 'Digital Photography' started by jdavtz, Jul 13, 2010.

  1. jdavtz macrumors 6502a

    Joined:
    Aug 22, 2005
    Location:
    Kenya
    #1
    Quick question:

    In same scenario, fixed subject, fixed background.

    Which should give more subject 'isolation' (not sure of the best word - i mean a more blurred background):

    135mm f/2 and crop to give same size subject as...
    200mm f/2.8 and don't crop

    Actual lenses not really so important -- I'm interested in how you work it out.

    (I would test it myself but have lent the 200mm lens to my sister).

    Thanks!
    Jonathan.
     
  2. Edge100 macrumors 68000

    Joined:
    May 14, 2002
    Location:
    Where am I???
    #2
    Here

    On full-frame...

    135 f/2, with subject at 30ft - DoF = 1.78 ft
    200 f/2.8, with subject at 30ft - DoF = 1.14 ft

    Cropping after the exposure wont affect DoF...using a crop sensor camera to get the same subject size WILL (by moving you further away from the subject).
     
  3. toxic macrumors 68000

    Joined:
    Nov 9, 2008
    #3
    cropping does affect DoF since it enlarges the image more.

    by cropping the 135mm image to match the 200mm FoV, you're simulating a 1.48x sensor. going to a DoF calculator and comparing 135/2 on 1.5x to 200/2.8 on 35mm, the 200mm has 5mm less DoF at 5m and 17mm less at 10m...which is much less than 1/3 of a stop, which means the difference is negligible.

    the 200mm image will likely look better, though, since it isn't enlarged as much.
     

Share This Page