pentax 50-200mm lens question

Discussion in 'Digital Photography' started by johnxsun@gmail.com, Sep 11, 2006.

  1. Guest

    Hi everyone,

    I recently bought ist dl with 18-55mm lens for my vacation and I loved
    it. Toady I bought the 50-200mm lens. I did some tests and have some
    questions here hope someone can help me out. Thanks in advance.

    When I set camera to AF with auto flash and try to focus on a dark
    point with pressing the shutter halfway, the flash just keeps flashing
    with a noise 'ZZZ...' until I release the shutter. It happened to the
    18-55mm lens once in a really dark place. But with 50-200mm lens that I
    just bought, it happened more, in some places it was ok with the
    18-55mm lens.

    Does the 50-200mm lens have any problem that causes it happened more,
    or it's just normal because it's a big lens?

    Thanks and regards,
    John
     
    , Sep 11, 2006
    #1
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  2. Paul Mitchum Guest

    <> wrote:

    > Hi everyone,
    >
    > I recently bought ist dl with 18-55mm lens for my vacation and I loved
    > it. Toady I bought the 50-200mm lens. I did some tests and have some
    > questions here hope someone can help me out. Thanks in advance.
    >
    > When I set camera to AF with auto flash and try to focus on a dark
    > point with pressing the shutter halfway, the flash just keeps flashing
    > with a noise 'ZZZ...' until I release the shutter. It happened to the
    > 18-55mm lens once in a really dark place. But with 50-200mm lens that I
    > just bought, it happened more, in some places it was ok with the
    > 18-55mm lens.
    >
    > Does the 50-200mm lens have any problem that causes it happened more,
    > or it's just normal because it's a big lens?


    You should try both lenses on the same subject matter in a darkened room
    for comparison.

    The flash comes on to help the camera autofocus by providing more light.

    The 18-55 is f/3.5, and the 50-200 is f/4. So all other things being
    equal, the 50-200 won't let as much light in. Thus, a longer hunting
    time for the autofocus, and more need for the focus-assist flash firing.
     
    Paul Mitchum, Sep 11, 2006
    #2
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  3. Roy G Guest

    <> wrote in message
    news:...
    > Hi everyone,
    >
    > I recently bought ist dl with 18-55mm lens for my vacation and I loved
    > it. Toady I bought the 50-200mm lens. I did some tests and have some
    > questions here hope someone can help me out. Thanks in advance.
    >
    > When I set camera to AF with auto flash and try to focus on a dark
    > point with pressing the shutter halfway, the flash just keeps flashing
    > with a noise 'ZZZ...' until I release the shutter. It happened to the
    > 18-55mm lens once in a really dark place. But with 50-200mm lens that I
    > just bought, it happened more, in some places it was ok with the
    > 18-55mm lens.
    >
    > Does the 50-200mm lens have any problem that causes it happened more,
    > or it's just normal because it's a big lens?
    >
    > Thanks and regards,
    > John



    Hi.

    Don't know your camera or lens.

    If the 55-200 is large, with perhaps an even larger lens hood on the front,
    could it be casting a shadow onto the area on which the lens is trying to
    focus.

    Roy G
     
    Roy G, Sep 11, 2006
    #3
  4. Guest

    Paul Mitchum wrote:
    > <> wrote:
    >
    > > Hi everyone,
    > >
    > > I recently bought ist dl with 18-55mm lens for my vacation and I loved
    > > it. Toady I bought the 50-200mm lens. I did some tests and have some
    > > questions here hope someone can help me out. Thanks in advance.
    > >
    > > When I set camera to AF with auto flash and try to focus on a dark
    > > point with pressing the shutter halfway, the flash just keeps flashing
    > > with a noise 'ZZZ...' until I release the shutter. It happened to the
    > > 18-55mm lens once in a really dark place. But with 50-200mm lens that I
    > > just bought, it happened more, in some places it was ok with the
    > > 18-55mm lens.
    > >
    > > Does the 50-200mm lens have any problem that causes it happened more,
    > > or it's just normal because it's a big lens?

    >
    > You should try both lenses on the same subject matter in a darkened room
    > for comparison.
    >
    > The flash comes on to help the camera autofocus by providing more light.
    >
    > The 18-55 is f/3.5, and the 50-200 is f/4. So all other things being
    > equal, the 50-200 won't let as much light in. Thus, a longer hunting
    > time for the autofocus, and more need for the focus-assist flash firing.


    Thanks, Paul,

    I did the tests on the exact same subjects with same condition. If it's
    not the lens problem, then I think the only difference is the size of
    the lens. The problem is I don't know for sure which one is the cause.
    >From what you saying, it seems that it is possible that the 50-200 can

    cause more flash firing than 18-55 does, right?

    Regards,
    John
     
    , Sep 11, 2006
    #4
  5. Paul Mitchum Guest

    <> wrote:

    > Paul Mitchum wrote:
    > > <> wrote:
    > >
    > > > Hi everyone,
    > > >
    > > > I recently bought ist dl with 18-55mm lens for my vacation and I loved
    > > > it. Toady I bought the 50-200mm lens. I did some tests and have some
    > > > questions here hope someone can help me out. Thanks in advance.
    > > >
    > > > When I set camera to AF with auto flash and try to focus on a dark
    > > > point with pressing the shutter halfway, the flash just keeps flashing
    > > > with a noise 'ZZZ...' until I release the shutter. It happened to the
    > > > 18-55mm lens once in a really dark place. But with 50-200mm lens that I
    > > > just bought, it happened more, in some places it was ok with the
    > > > 18-55mm lens.
    > > >
    > > > Does the 50-200mm lens have any problem that causes it happened more,
    > > > or it's just normal because it's a big lens?

    > >
    > > You should try both lenses on the same subject matter in a darkened room
    > > for comparison.
    > >
    > > The flash comes on to help the camera autofocus by providing more light.
    > >
    > > The 18-55 is f/3.5, and the 50-200 is f/4. So all other things being
    > > equal, the 50-200 won't let as much light in. Thus, a longer hunting
    > > time for the autofocus, and more need for the focus-assist flash firing.

    >
    > Thanks, Paul,
    >
    > I did the tests on the exact same subjects with same condition. If it's
    > not the lens problem, then I think the only difference is the size of
    > the lens. The problem is I don't know for sure which one is the cause.
    > From what you saying, it seems that it is possible that the 50-200 can
    > cause more flash firing than 18-55 does, right?


    I'm saying that an f/4 lens won't let in as much light as an f/3.5 lens,
    making it more difficult for the autofocus system to work.
     
    Paul Mitchum, Sep 12, 2006
    #5
  6. In article <1hlidac.x0zhlj1i7c5y9N%0m>, 0m
    (Paul Mitchum) wrote:

    > I'm saying that an f/4 lens won't let in as much light as an f/3.5 lens,
    > making it more difficult for the autofocus system to work.


    Paul-

    The kit lens that came with my *ist DS, has an f/3.5-f/5.6 aperture. In
    other words, it is f/5.6 at the telephoto end.

    I suspect Roy may have hit the nail on the head by suggesting the large
    50-200mm lens was physically blocking the flash beam. Even with the kit
    lens, the DS instruction manual (page 49) says to remove the lens hood.
    It also has a table of lens-flash compatibility (page 151) but the
    50-200mm lens is not listed.

    That table also assumes the lens hood has been removed. It is possible
    the 50-200mm lens is too big even without a hood.

    Fred
     
    Fred McKenzie, Sep 13, 2006
    #6
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