Problem with my D40?

Discussion in 'Digital Photography' started by Ridge08, Mar 18, 2009.

  1. Ridge08 macrumors member

    Joined:
    Feb 2, 2009
    #1
    So the D40 has three focus points running in a line across the middle of the frame. In the last couple weeks, I`ve noticed the left and right points searching quite a bit, struggling to lock onto the subject.

    This has happened in good light with stationary targets. I`m talking 1/320 at f/8. The subject for that particular exposure was about 15 feet away and had clearly-defined edges. It was an off-white colored pagoda on a hilltop, the focus being on one of the pillars holding the roof up.

    There have been other occasions too, though I can`t supply specific data. But as an estimate, the other day I was photographing a white, smooth object in low light (street lamps at night), again at a distance of about 15 feet. This time there was no distinct edge but I hoping for a bit more from the camera.

    On these occasions, I`ve almost always been able to focus using the middle point, hold the AE/AF lock and recompose - though even this sometimes doesn`t work for soft-shaped clouds.

    Do you think my D40 is faulty? Has anyone had similar issues?

    I bought the camera two months ago and haven`t done anything to damage it. There`s a one-year warranty.

    Now I think about it, there`s something else: if I understand things correctly the dynamic area focus mode is supposed to allow to to set your initial point of focus, which will move if the subject moves across the frame. I`m not convinced mine moves with the subject, though it may have to do with the subject: birds in flight - though not at any enormous distance and not moving that quickly.

    If there`s a fault, I might try to trade up to a D90. Whether that`s possible or not, I`m gonna be annoyed if there`s not a problem!
     
  2. telecomm macrumors 65816

    telecomm

    Joined:
    Nov 30, 2003
    Location:
    Rome
    #2
    Maybe someone else can comment about whether the centre focal point is better able to achieve focus, but the situations you're describing sound like textbook examples of situations in which autofocus is likely to fail: soft clouds, smooth white objects in low light with no hard edges...

    I wouldn't expect that there's a problem with your camera.
     
  3. Ridge08 thread starter macrumors member

    Joined:
    Feb 2, 2009
    #3
    Two specific examples, both clickable. Both shot in raw with no post processing. Nikon D40 and 18-55mm kit lens.

    Shutter speed: 1/320 with +1.67 exposure compensation (so the meter was actually suggesting 1/1000).
    Aperture: f/8.
    ISO: 200.
    Pagoda about 15 feet away.
    Both right and left focus points refused to lock onto the vertical column in the middle of the photo (shot in raw, zero post processing).
    [​IMG]


    Shutter speed: 1/40.
    Aperture: f/5.6.
    ISO: 200.
    Shirt hanging five feet away. Flourescent 67W light hanging from the ceiling four feet in front of the shirt. Funny how much darker this one looks on the photo than in real life (though nothing done to the raw file in post). The crease running down the middle is two inches deep. Right and left focus points couldn`t find any point on this crease. They also couldn`t lock onto the point where the white body meets the green sleeve, or onto the right edge of the sleeve.
    [​IMG]

    Then I turned the camera into portrait orientation and the focus points found the crease in the middle immediately!

    In all cases, for both photos, the middle focus point found the target instantly.
     
  4. leighonigar macrumors 6502a

    Joined:
    May 5, 2007
    #4
    It's working fine, cross vs straight focus points in low light. That's all.
     

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