Hard time focusing 50mm/f1.8

Discussion in 'Photography Beginners' Forum' started by matt62485, Jan 12, 2010.

  1. matt62485

    matt62485 TPF Noob!

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    So I recently got a 50mm/f1.8 for my D40, fully aware it would not autofocus on this body. However, I'm having one hell of a time getting this thing to focus. Being a prime with a fixed focal length and no auto focus, is a tripod neccessary to really make this thing shine? :confused:

    Any advice?
     
  2. Goontz

    Goontz TPF Noob!

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    Tripod isn't necessary, but sometimes just the amount you "sway" while holding it can throw the focus off and it can be especially hard to nail focus with real large apertures. Are you aware of the focus light in the bottom-left corner of your viewfinder that tells you when you're in focus?
     
    Last edited: Jan 12, 2010
  3. KmH

    KmH Helping photographers learn to fish Supporting Member

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    Kevin raises a good point.

    At f/1.8 your DOF (depth-of-field) will be shallow. Very shallow if you are close to your subject.
    According to DOF Master at f/1.8 and 2 feet from your point of focus your total DOF is only .03 feet or about 1/3 rd of an inch and 1/2 of that is in front of the focus point and 1/2 is behind the focus point.

    If you move back to 10 feet from the point of focus, with the aperture at f/1.8 the total DOF is now about 16 inches for the same aperture.
     
  4. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Actually I think it's closer to 2/3 behind the focus point and 1/3 in front....but who's counting? ;)
     
  5. matt62485

    matt62485 TPF Noob!

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    good gracious. no wonder, that makes perfectly good sense. thanks!

    and Goontz, yes I'm aware of it, thats what I go by and 99% of the time, upclose at f1.8 its such a slight bump of the focus ring, it kinda of blinks in and out bc im apparently not to steadhand
     
  6. KmH

    KmH Helping photographers learn to fish Supporting Member

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    As a general rule, but at short working distances and wide apertures (2 feet at f/1.8) it's virtually 50/50.
     
  7. shanemono4

    shanemono4 TPF Noob!

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    can you tell me more about this focus light in the bottom left corner? Is it d40 specific?
     
  8. SushiWarrior

    SushiWarrior TPF Noob!

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    It's a light in the bottom left corner of the screen - it'll flash green. My technique is setting it on continuous shooting mode and taking a burst while moving the ring, which generally gets at least 1 in focus shot.
     

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