Slow auto focus when photographing trick-or-treaters.

Discussion in 'Digital Photography' started by Daniel Prince, Nov 13, 2006.

  1. This year I photographed trick-or-treaters for the first time. I
    sat out on my front porch with the porch light on. (The porch light
    is a white compact florescent. I do not know what the color
    temperature of the light is or what the wattage is.) The porch
    seemed fairly bright to me.

    I have a Minolta Z5. The view through the EVF was rather dark and
    the camera took a long time to focus and take a shot. Would
    increasing the light level on the porch solve this problem or would
    it be better to just set the camera to focus at about four feet and
    take the pictures that way?

    Is there some other adjustment I could make that would give me
    faster shots under these conditions? Thank you in advance for all
    replies.
    --
    Never ever let your brain explode. It's VERY bad for you and
    it leaves a terrible mess for someone to clean up.
     
    Daniel Prince, Nov 13, 2006
    #1
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  2. Daniel Prince

    ASAAR Guest

    On Mon, 13 Nov 2006 00:41:49 GMT, Daniel Prince wrote:

    > I have a Minolta Z5. The view through the EVF was rather dark and
    > the camera took a long time to focus and take a shot. Would
    > increasing the light level on the porch solve this problem or would
    > it be better to just set the camera to focus at about four feet and
    > take the pictures that way?


    Increasing the light level should help. Most P&S cameras take
    longer to focus when light levels are low. Presetting the focus
    would certainly eliminate the focus time, whether fast or slow. But
    at low light levels you'd probably have the camera using a large
    aperture, and with large apertures comes shallower depth of field,
    which can cause sharpness problems if your preset focus distance
    doesn't quite match the subject's actual distance.

    My camera (Fuji S5100) has its own focusing idiosyncrasies which
    may or may not match your Z5, but I'll mention some and you can see
    how the Z5 compares. Focusing in dim light is only slightly slower
    if the AF-assist illuminator is disabled, but when it is enabled,
    focusing is more accurate. The manual mentions that the AF-assist
    illuminator isn't particularly effective when the lens is zoomed to
    the tele end, about 6x or more, so the lens should be set to a wider
    tele position when using the AF illuminator.

    There are also different recommended subject distance ranges
    depending on whether macro mode is on or off. These ranges overlap,
    with macro mode being effective up to 6.6 feet, and normal mode down
    to 3 feet. I thought that I recalled focusing becoming slower and
    less accurate as the subject distance dropped to below 5 feet, and
    switching to macro mode helped. But I just tried it and focusing
    remained quick and accurate in normal mode even down to 3 feet. The
    only thing I can think of at the moment is that the batteries are
    fresh, so perhaps focusing suffers a bit when the batteries aren't
    fully charged or fresh.

    The camera used also matters. I recently tried the S5200 (which
    replaced the S5100 about a year ago?) and focusing is much better
    and the EVF display is much brighter in low light.

    Oops. I just checked the dpreview's review of the Z5, and while
    it initially indicated that its focus performance should be good
    ("Fastest-in-class*1 Rapid AF with Predictive Focus Control"), the
    review eventually disclosed a Z5 weakness:

    > Our only other major complaint is focus, which seems to hunt
    > excessively in low light or with low contrast subjects, and - as
    > with other Konica Minolta cameras we've tested - will on occasion
    > indicate correct focus when it hasn't been found, resulting in a
    > totally out of focus image.

    http://www.dpreview.com/reviews/konicaminoltaz5/page6.asp

    I think that I recall this also being a problem with K/M's A2
    and/or A200. Short of upgrading to a newer camera (and that's hard
    to do if you want to stick with K/M) you might want to experiment
    with better lighting on your porch (multiple lights would more
    advantages than just increased brightness) and the prefocusing
    technique that you mentioned.
     
    ASAAR, Nov 13, 2006
    #2
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  3. Daniel Prince <> wrote:
    : This year I photographed trick-or-treaters for the first time. I
    : sat out on my front porch with the porch light on. (The porch light
    : is a white compact florescent. I do not know what the color
    : temperature of the light is or what the wattage is.) The porch
    : seemed fairly bright to me.

    : I have a Minolta Z5. The view through the EVF was rather dark and
    : the camera took a long time to focus and take a shot. Would
    : increasing the light level on the porch solve this problem or would
    : it be better to just set the camera to focus at about four feet and
    : take the pictures that way?

    : Is there some other adjustment I could make that would give me
    : faster shots under these conditions? Thank you in advance for all
    : replies.

    Compact florescents are bad about fooling cameras (due to the rapid on-off
    cycle) and also tend to give a green cast to images (in my experience).
    You probably would have been better with a high wattage incandescent and
    setting the white balance apropriately.

    The reason the AF was slow (most likely) was because the camera was
    detecting low light. Just setting to a specific focus may be a good idea,
    but can be tricky. For some lenses (like wide angle lenses) the point at
    which "infinity" begins may be 5 or 6 feet, and so setting the camera to
    infinity and letting it go makes sense. But for some lenses (such as my
    tele zoom) infinity does not begin until 25 feet. Distances closer than
    that may be a bit critical about focus (very narrow depth of field) and so
    if your subject is a foot or so off your best focus will be blurry.

    So if you add one or more high wattage (100w or more) light to your porch,
    and/or use a wide angle lens, while standing at or beyond the point at
    which your lens focus is counting as infinity you may be ok. Of course
    now that Halloween is past you can spend the next year experimenting with
    various ideas to find the best choice for your situation. :)

    Randy

    ==========
    Randy Berbaum
    Champaign, IL
     
    Randy Berbaum, Nov 13, 2006
    #3
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