Bottom half of split image turns black, whatsup?

Discussion in '35mm Cameras' started by nonamegiven, Jan 19, 2004.

  1. nonamegiven

    nonamegiven Guest

    Recently, when focusing with the split image in the viewfinder of my
    old Pentax Super Program, the bottom half of the circle turns black.
    What could cause this? Its the same on every lenses.
    nonamegiven, Jan 19, 2004
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  2. nonamegiven

    Phil Cole Guest

    Not sure what causes this, but it happens on my FE2 when doing macro work.

    Phil Cole, Jan 19, 2004
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  3. nonamegiven

    Mike Guest

    Usually caused when your eye is not aligned with the center of the circle
    containing the split.
    Try tilting the camera up or down a little.
    Mike, Jan 19, 2004
  4. nonamegiven

    Francis Roy Guest

    Anytime you have a split image focusing spot and the f opening goes
    smaller than f4 or f5.6 , one half will go black. It's an optical law.
    There is nothing you can do about it. If you move your eye along the
    split line the darkend half will move from one side to the other.
    If you want to check this, try a normal lens set at f5.6. Start with the
    lens wide open then use your Depth of field lever/button to stop the
    lens down. You will see that the split will darken.

    Francis in VT
    Francis Roy, Jan 19, 2004
  5. It generally happens when the aperture of the lens gets smaller. It is
    just a matter of the way the aperture and the design of the rangefinder.
    The more sensitive (easy to see) the rangefinder is, the wider the aperture
    it needs.
    Joseph Meehan, Jan 19, 2004
  6. nonamegiven

    Waltavion Guest

    This typically happens in a low light situation. Try putting the center circle
    of the split image on a brighter area of the scene if you can without altering
    the focus.

    Walt McKinney
    Moncks Corner, SC
    Waltavion, Jan 21, 2004
  7. Actually, it happens when the taking lens has too small an aperture for
    this type of focusing, and has nothing to do with the amount of light
    on the scene.

    You can sometimes partially overcome this by carefully positioning your
    eye in the eyepiece.
    Scott Schuckert, Jan 21, 2004
  8. nonamegiven

    Rudy Garcia Guest

    To add to this thread some more information:

    The design of the split image prisms used is a tradeoff between how
    sensitive to focusing errors they are versus the max f-stop of the lens
    used. If you want a high degree of focusing sensitivity, you need a
    more aggressive set of prisms (in respect to the angle of the prism
    surface). This however requires a faster lens. So, most split image
    aids crump out when the lens aperture gets to be around f8 or so. That
    is one reason why pro cameras offer interchangeable screens. Slow lenses
    can be more easily focused on a plain matte screen with no split image
    aid in the middle.
    Rudy Garcia, Jan 22, 2004
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