Can shutter speed determind focal point?

Discussion in 'Photography Beginners' Forum' started by mooker, Sep 20, 2006.

  1. mooker

    mooker TPF Noob!

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    Today on my lunch break I ventured out and took some pics. I saw a tree with some red berries on it that stood out from the rest of the field. I took two pictures with a fixed aperture of f/2.8. As you can see in the pictures, the focal point changed from the background in image one to the branch in image 2. My intention was for the focus to be on the branch, and not the background. Here are the images.

    Image One
    Image Two

    Each pic contains the EXIF data, but I'll list them here and save you some time :D.

    Image One EXIF
    Image Two EXIF

    Unless I'm missing something, it appears that only the shutter speed or Tv has changed. Is the differing shutter speed causing the change in focus, or is it my Auto-Image Auto-Focus on the camera? If it's the latter, I'm not sure how the camera decides on the focal point. As you can see in comparing the pictures, the shot angle has slightly changed, and maybe that's caused the focus to change. I dunno. Any thoughts?

    Thanks!
     
  2. Big Mike

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

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    In one image, you were focused on the berries. In the next image, the AF missed the berries and therefore focused on the background. Your EXIF does not record the focus position or distance to subject.
     
  3. JDS

    JDS TPF Noob!

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    I don't really know how your camera's AF works either, but here's what happened:

    In Image 1, it focused and metered on the trees in the background. Those trees are in the sunlight, so it used a faster shutter speed.

    In image 2, it focused and metered on the branch in the foreground. That branch is in the shade, so it used a longer shutter speed to compensate for the slightly lesser amount of light.
     
  4. mooker

    mooker TPF Noob!

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    Aha, thanks for the info. I believe instead of auto-focus I had it on manual focus (manual being you pick the part of the LCD screen that you want it to focus on). When I moved my camera slightly, it must have chose the branch instead of the background as you have suggested.
     
  5. Big Mike

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

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    I don't know much about those digi-cams...but manually picking the area in which to focus...is different than what we would call manual focus. Manually focusing would be if you were adjusting the focus based on what you see...not what the camera sees.

    I don't know if you would be able to tell what is in focus...with the LCD screen...but that would be one way to check what the camera is focused on.
     
  6. mooker

    mooker TPF Noob!

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    Yep, you're right. That's all the focusing I can do with my digital camera. The closest I can come to manual focus is in macro mode, it will let me specify the distance to the object that I'm shooting.
     

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