Focus wrong? Need help testing Kodak DX7630 AF

Discussion in 'Kodak' started by Dave G, May 13, 2005.

  1. Dave G

    Dave G Guest

    I'm getting (possibly) wrong focusing w/my DX7630 autofocus. It seems
    to be setting the lens about 2/3 of the way to what I would consider
    the target.

    Before I send it back to Kodak on warranty, I want to see if it's
    something I'm doing.

    What's the right way to test?

    (There's no way to set focus manually on this model).

    My latest tests involve long-distance focus with a tripod, with and
    without the Retinar 0.6x wide angle converter lens. The scene is on a
    flood control bank of a river with sharp riprap extending from camera
    position to the far distance as well as forest on the other side. The
    figures below refer to the furthest that trees/riprap are the
    sharpest.

    W/o the WA lens, with center focus, camera pointed so that the focus
    target includes the line between trees and sky on a hill about 1 mile
    away, the point of sharpest focus on the photo file is about 800 yards
    away. The treeline in the distance is noticeably soft.

    With the WA converter, same focus setup, the point of sharpest focus
    is about 300 yards away, an odd bit of data. While this may be
    distortion/degradation from the add-on lens, there seems to be no
    focus problems with it when taking architectural subjects about 50-300
    yards away.

    With the camera on "landscape" mode and also landscape SCN mode,
    results are about about the same. From emails to Kodak support, I've
    learned that "landscape," rather than setting the lens at inifnity ,
    instead sets the camera on multi-zone focusing. (Not sure what that's
    about -- I'd think than landscape shots would benefit most from a lens
    set to infinity).

    Similarly, in "macro" mode, focus at a nice sharp target at 9"
    (keyboard) sets the lens so that I have to move the camera (with
    shutter button half down) a few inches closer for sharpest focus.

    Any help is welcome.
    Dave
     
    Dave G, May 13, 2005
    #1
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  2. Dave G

    Ron Hunter Guest

    Let me see if I understand. You claim that at a distance of 800 yards
    focus is good, but things farther away aren't sharp? So, why do you
    think there is a focus problem? Maximum focus variation is in the range
    of 20 to 50 feet, anything farther away is 'infinity' as far as the lens
    is concerned. The lack of sharpness of objects farther away than 800
    yards is due to the fact that the size of an object at that distance is
    quite probably less than one pixel in size, and thus can't be rendered
    clearly. There is a level at which even a 6 mp sensor can't get enough
    of an image to produce a clear definition.
     
    Ron Hunter, May 14, 2005
    #2
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  3. Dave G

    Dave G Guest

    Because in certain situations, the DX7630's focus is softer than my
    1990 Fujifilm 1400 zoom (1.4 Mp). With the Schneider lens and lots
    more pixels, shouldn't the Kodak be better?
    As a focus newbie, I don't quite understand this. The camera focuses
    well on things up to around 900 yards... 2700 feet... ?
    Hadn't thought of that, so I went back to one test image. A large pine
    tree jutting out into the sky about 1 mile away is quite soft. The
    smallest masses, branches toward the top, are 4 pixels across, and
    other elements of the tree are 20-30-50 pixels across.

    The full image is at http://www.un-real-estate.com/images/100_0679.JPG
    Pine tree in question is along the skyline just to the left of center.
    The bridge is 800 yards away. To my eyes, the furthest area of sharp
    focus is the trees just behind the bridge. But, admittedly, I don't
    really know what to look for.

    This was one I took with center spot focus. According to the AF
    brackets, I was focusing on the area where the pine tree juts out.
    Camera at wide angle (no WA conversion lens attached). Tripod; 1/250;
    f/6.7. Compression: fine. Sharpening: normal. 6.1 Mp.
     
    Dave G, May 14, 2005
    #3
  4. Dave G

    Ron Hunter Guest

    Not always. The large pixels of the lower resolution cameras give an
    illusion of great 'sharpness', since their edges are more apparent.
    Take a picture of the same thing from the same viewpoint, and zoom, and
    look at each. The lower resolution at 50% on your screen will probably
    appear sharper. Now magnify each of them to 200%. Now which one has
    more DETAIL? Which one appears sharper. Surprised? I was.
    The picture with the more pixels will appear less sharp because the
    extra pixels make lines that appear sharp (if somewhat ragged) while the
    greater number of pixels reveals more detail, but appears less sharp.
    In either case, picture elements are only so large, and if an object is
    so far away that the lens casts the whole image on only a single pixel,
    it WILL appear fuzzy.
     
    Ron Hunter, May 14, 2005
    #4
  5. Dave G

    Ronald Baird Guest

    Hi Dave,

    Sorry I wasn't here for the last few days. Was off on an assignment and
    vacation.

    If you have a couple of images that were taken at WA and Tele I will be glad
    to review and examine. I would like to review the picture quality as well
    as measure for perspective. Do you have an accessory lenses? Also have you
    tried resetting the camera to its defaults. If not try doing this to see if
    it makes a difference. This should make sure the camera is set to perform
    normally as out of the box. You can simply remove the batteries from the
    camera overnight and the camera will be reset.

    Let me know and send along some pictures. I will review and reply to you, as
    well as post here if you like.

    Talk to you soon,

    Ron Baird
    Eastman Kodak Company
     
    Ronald Baird, May 20, 2005
    #5
  6. Dave G

    ASAAR Guest

    To be honest, to me it doesn't appear to be any more out of focus
    at the greatest distance than it does at some of the closer parts of
    the picture. It may appear that way because of the bright
    backlighting of the sky leaking through the most distant objects. I
    don't know if your manual mentions it, but the one for my Fuji
    describes the types of objects that are suitable for focusing and
    types of objects that don't work very well. Not only is the
    'jutting' pine tree a poor object to focus on, there really isn't
    any distant object that's suitable either. It may be that your
    camera focused much closer than you suspect. Just because you
    placed the pine tree in the focusing brackets doesn't guarantee that
    your camera (or any AF camera) will be able to focus accurately on
    that object. The focusing mechanism needs clearly defined
    horizontal or vertical edges and contrasting colors. This is the
    type of picture where I think a manual focusing lens would be able
    to focus more quickly and more accurately. Does your camera have a
    "landscape" picture mode that might force the camera to focus at a
    great distances? To get a better idea of where the camera actually
    is focusing you might want to maximize the lens's aperture.
    Whatever is closely in focus should appear about the same as in your
    picture, but the out of focus areas will be much more blurred.
     
    ASAAR, May 21, 2005
    #6
  7. Dave G

    Ron Hunter Guest

    Yes, the camera has a landscape setting, and the OP needs to read his
    manual, and follow the advice in it. Setting the camera on landscape
    will set 'infinity' for focus, greatly reducing both the time, and
    energy drain for taking such pictures, and will then adjust the exposure
    and aperture for good depth of field. Manual focus is never as fast as
    AF, unless the camera has very poor autofocus performance. I have NEVER
    seen a manual focus I can adjust in less than .2 seconds.
     
    Ron Hunter, May 21, 2005
    #7
  8. Dave G

    ASAAR Guest

    Nor I, but for the type of picture we're discussing (where the
    camera's AF has nothing good to focus on) even if it takes 5 seconds
    to focus manually, you're assured of getting a pretty accurate
    focus. For the same difficult subject, the camera using AF would
    either focus inaccurately (albeit relatively quickly, which is
    useless) or would waste a lot of time 'hunting', without assuring
    the photographer that the picture would be focused properly when it
    finally stops. This last, BTW points out a limitation with optical
    viewfinders, at least in the digital P&S cameras I've seen. If the
    camera is misfocused you have no indication of it, only an
    indication that the camera has focused on something, somewhere.
    Only by looking at the LCD display (or an EVF), with sufficient
    resolution and perhaps a zoomable center area, can you tell if the
    camera is focused where it's intended to be.
     
    ASAAR, May 21, 2005
    #8
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