advice on autofocus with canon's nifty-fifty

Discussion in 'Digital Photography' started by fongyuen, Mar 24, 2011.

  1. fongyuen macrumors 6502

    Joined:
    Jun 9, 2007
    #1
    i've had this lens for about 7 months now and while i think it's a great lens, how to get consistent focus with the AF is still a mystery to me. i generally shoot around 1.8 to 2.2 so i know the dof is pretty shallow and perhaps that is part of the reason, but when i shoot, i generally use the center point, focus on the eyes or some part of the face and then reposition. sometimes it comes out the way i want, as in this example, other times, the focus seems to be on something else, not where I had intended (the water gun is in focus but i wanted the face to be). any advice on what i need to change in my methodology? thanks.
     
  2. robbieduncan Moderator emeritus

    robbieduncan

    Joined:
    Jul 24, 2002
    Location:
    London
    #2
    I would suggest this could be the problem: when you reposition you are probably altering the distance between the lens and the subject somewhat.
     
  3. fcortese macrumors demi-god

    fcortese

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    Apr 3, 2010
    Location:
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    #3
    Agree with robbie, with that shallow a DOF when you reposition if you're off a little the focus might change. Try using a DOF of 4 and see what happens. Your bokeh effect will obviously be different but you may have more consistent pictures. FWIW
     
  4. Edge100 macrumors 68000

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    May 14, 2002
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    Where am I???
    #4
    The second example is really significantly front-focused, and is shot at f/2.8, so I don't think your focus and recompose technique is to blame (I'd expect a lot less change in focus using the slight focus and recompose you've used here).

    Did you lock focus on the eyes and then recompose? Is it possible that you re-focused after you recomposed?
     
  5. wilhelmreems macrumors member

    Joined:
    May 25, 2010
    #5
    i had a similar problem with my nikon 50mm, inconsistent focus and hunting for focus, even after i locked it. Problem was, I thought i locked it, but i didn't check the settings on the camera iteself. I was set up for continuous focus instead of single focus, which accounted for the lens hunting and refocusing everytime i tried to compose a shot.

    not sure if this helps, but once i did realize my error of not resetting the camera for what i was trying to do, the problem was gone.
     
  6. fcortese macrumors demi-god

    fcortese

    Joined:
    Apr 3, 2010
    Location:
    Big Sky country
    #6

    Both of these sound like a good analysis of what may ahve caused your issues. I have a nifty 50 which I got recently but have only had it out once so far and did not notice any issues. But I was not doing potrait like fotos either. good luck.
     
  7. fongyuen thread starter macrumors 6502

    Joined:
    Jun 9, 2007
    #7
    yeah, i can try to take notice of this next time, but i don't think i'm moving that significantly forwards and backwards or laterally, esp. as you pointed out, the recompose distance isn't all that much. nonetheless, i'll try to be more careful next time.

    i'm definitely on One Shot AF rather than AI Servo so that shouldn't be it, but i haven't not tried locking the focus. i'll give that a try, thanks!
     

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