a5000 AF

Discussion in 'Sony Alpha E-Mount Cameras' started by nighttrain, Apr 4, 2015.

  1. nighttrain

    nighttrain TalkEmount Regular

    Dec 9, 2014
    My a5000 seldom focuses correctly on close objects. I don't go any closer than the minimum focusing distance of the lens. I usually have to press the shutter half way down several times before I get green focus indicators wide enough to cover most of the subject. But the focus indicators almost never cover the entire object I'm shooting, and only part of it will be in focus. (I've tested outdoors with plants and flowers, in the house with objects in the kitchen, etc.) I set the AF to wide but it doesn't seem to help. If I step back and take a wider shot than I want, the subject will be in focus. Is there something else I can do to improve the focus accuracy? Is this just a limitation of the camera's AF?
  2. michelb

    michelb TalkEmount Veteran

    Oct 27, 2013
    Greater Montreal area in Quebec, Canada
    Michel Brien
    At very close distance there is a phenomenon called: Depth of Field that get more and more limited as you get close to a subject.

    To maximize depth of field, your aperture number ( F-number) should be high when you take the picture ( F16 or F22 ) otherwise only a portion of the subject will be in focus. But then your shutter speed will be slower making it more difficult not to move when taking the picture otherwise it will be all blurry.

    For example, using a 50mm F 1,4 lens focused at 3 feet gives you an approximate depth of field of:
    1 inch ( 25mm ) at F 1.4 ( about 1/2 inch front and back of your subject )
    4 inch ( 100mm ) at F 5,6 ( about 1 3/4 inch front and 2 1/16 inches back of your subject )
    11 inches ( 275mm ) at F 16 ( about 4 5/16 inches front and 6 5/8 inches back of your subject )

    Focused at 1,5 ft:
    1/4 inch ( 6mm ) at F 1.4 ( about 1/8 inch front and back of your subject )
    3/4 inch ( 19mm ) at F 5,6 ( about 1/4 inch front and 1/2 inch back of your subject )
    2 inches ( 50mm ) at F 16 ( about 3/4 inch front and 1 1/4 inch back of your subject )

    These will also change with focal length a bit but not by much at very close range.

    Check your pictures EXIF on the computer, my guess is your camera took the shots at maximum aperture of F 3,5 to f 5.6 assuming you have the 16-50 zoom
  3. nighttrain

    nighttrain TalkEmount Regular

    Dec 9, 2014
    Thanks for your reply michelb. I have high f-stops on my outdoor shots, but not high enough on indoor tests. So the problem may be a combination of f-stop and hand shake. I'm now using a Sigma 30 instead of the 16-50.
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