Infinity... isn't

Discussion in 'Digital Photography' started by jmc, Jan 22, 2007.

  1. jmc

    jmc Guest

    I've been noticing that on my Tamron 17-50mm lens, in manual focus mode
    if I run the ring out to the infinity end, it goes out of focus.
    Infinity focus is just in from the end of the ring's turn. If that
    makes sense...

    Is this normal? I'm new to DSLRs and their lenses. It's really
    annoying when trying to do sky photography, makes it nearly impossible
    (and somewhat a matter of luck) to get sharp night images.

    Thanks for any help.

    jmc
    jmc, Jan 22, 2007
    #1
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  2. jmc

    M-M Guest

    In article <>,
    jmc <> wrote:

    > Infinity focus is just in from the end of the ring's turn. If that
    > makes sense...



    Same with my Nikon lenses. I was wondering about that also.

    --
    m-m
    M-M, Jan 22, 2007
    #2
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  3. jmc

    Paul Rubin Guest

    jmc <> writes:
    > I've been noticing that on my Tamron 17-50mm lens, in manual focus
    > mode if I run the ring out to the infinity end, it goes out of
    > focus. Infinity focus is just in from the end of the ring's turn. If
    > that makes sense... Is this normal?


    It's not that uncommon, and it's normal in certain types of fancy
    lenses and telescopes, but for a random consumer lens like that 17-50
    it means the infinity stop slightly out of adjustment.

    Anyway, it shouldn't be a real problem with normal MF technique.
    Basically focus the lens all the way to the infinity stop (which can
    mean slightly past actual infinity). You can develop a reflex for
    doing that simultaneously with lifting the camera to your eye. Camera
    makers like Nikon and Pentax make their lenses all consistent in the
    direction of rotation towards infinity so that you can do that by
    reflex. However they didn't all make the same choice, so clockwise
    and counterclockwise are sometimes called "the Nikon direction" and
    "the Pentax direction" (I'm not sure which one Canon uses).

    Once the camera is at eye level, focus away from infinity while
    watching the finder screen. You can do this pretty quickly (go for
    speed and smoothness rather than precision) and you will see the image
    come into focus. Stop turning when that happens, which means you will
    overshoot a bit. Then turn the lens in the other direction more
    carefully, stopping just at the point of correct focus using the split
    image prism (oh yes, you need a focusing screen with split image
    prism, normal on MF SLR's but a special upgrade for most DSLR's, sigh).

    You should not overshoot in this second operation. Focusing is three
    steps: 1) set lens to infinity by feel, without having to look at it;
    2) coarse focus, overshooting focus point; 3) precise focus, just a
    slight adjustment to the coarse focus. You should not need to hunt
    back and forth or otherwise mess around like beginners often do. This
    technique takes a little bit of practice but once you get the hang of
    it, at least on non-moving subjects you can focus almost as fast as an
    AF system can.
    Paul Rubin, Jan 22, 2007
    #3
  4. jmc

    Dave Cohen Guest

    M-M wrote:
    > In article <>,
    > jmc <> wrote:
    >
    >> Infinity focus is just in from the end of the ring's turn. If that
    >> makes sense...

    >
    >
    > Same with my Nikon lenses. I was wondering about that also.
    >

    I used to see that with a third party zoom on my canon slr. Surprised it
    would happen with original lenses though.
    Dave Cohen
    Dave Cohen, Jan 22, 2007
    #4
  5. jmc

    jdear64 Guest

    M-M wrote:
    > In article <>,
    > jmc <> wrote:
    >
    > > Infinity focus is just in from the end of the ring's turn. If that
    > > makes sense...

    >
    >
    > Same with my Nikon lenses. I was wondering about that also.
    >
    > --
    > m-m


    This is normal for long focal length lenses. Some atmospheric
    conditions can require focusing past infinity. At least this is what I
    read somewhere. Not sure if I ever focused passed infinity since
    there's no way to know.

    John
    jdear64, Jan 22, 2007
    #5
  6. jmc

    Paul Bartram Guest

    "jmc" <> wrote

    > I've been noticing that on my Tamron 17-50mm lens, in manual focus mode
    > if I run the ring out to the infinity end, it goes out of focus.
    > Infinity focus is just in from the end of the ring's turn. If that
    > makes sense...


    That last little bit takes you into ... The Twilight Zone. This setting is
    used by people taking blurred photos of UFOs and of Elvis through the window
    of McDonalds.

    Seriously though, didn't lenses in the good old film days have an 'IR'
    setting because infra red light focuses differently? (Maybe wrong on that!)

    Paul
    Paul Bartram, Jan 22, 2007
    #6
  7. jmc

    Paul J Gans Guest

    M-M <> wrote:
    >In article <>,
    > jmc <> wrote:


    >> Infinity focus is just in from the end of the ring's turn. If that
    >> makes sense...



    >Same with my Nikon lenses. I was wondering about that also.


    It is done on purpose. I believe that the autofocus mechanism
    has to be able to go past the best focus in order to know
    that that's the best focus.

    But we hates it. It means that I cannot even manually focus
    for infinity.

    --
    --- Paul J. Gans
    Paul J Gans, Jan 22, 2007
    #7
  8. jmc

    Roy G Guest

    "jmc" <> wrote in message
    news:...
    > I've been noticing that on my Tamron 17-50mm lens, in manual focus mode if
    > I run the ring out to the infinity end, it goes out of focus. Infinity
    > focus is just in from the end of the ring's turn. If that makes sense...
    >
    > Is this normal? I'm new to DSLRs and their lenses. It's really annoying
    > when trying to do sky photography, makes it nearly impossible (and
    > somewhat a matter of luck) to get sharp night images.
    >
    > Thanks for any help.
    >
    > jmc


    Hi.

    The best explanation I have heard of for the extra travel built into lenses
    is to allow for extremes of temperature, causing the barrel to alter its
    actual length.

    Without that bit of spare, it might then not be possible to get infinity
    focus.

    Roy G
    Roy G, Jan 23, 2007
    #8
  9. jmc

    Annika1980 Guest

    jmc wrote:
    > I've been noticing that on my Tamron 17-50mm lens, in manual focus mode
    > if I run the ring out to the infinity end, it goes out of focus.
    > Infinity focus is just in from the end of the ring's turn. If that
    > makes sense...
    >
    > Is this normal? I'm new to DSLRs and their lenses. It's really
    > annoying when trying to do sky photography, makes it nearly impossible
    > (and somewhat a matter of luck) to get sharp night images.


    Tell me about it! My stereo goes all the way to 11.
    Annika1980, Jan 23, 2007
    #9
  10. jmc

    M-M Guest

    In article <ep3j42$dqs$>,
    Paul J Gans <> wrote:

    > It is done on purpose. I believe that the autofocus mechanism
    > has to be able to go past the best focus in order to know
    > that that's the best focus.



    This appears to be the most sensible explanation so far.

    --
    m-m
    M-M, Jan 23, 2007
    #10
  11. jmc

    ASAAR Guest

    On 22 Jan 2007 16:32:48 -0800, Annika1980 wrote:

    >> Is this normal? I'm new to DSLRs and their lenses. It's really
    >> annoying when trying to do sky photography, makes it nearly impossible
    >> (and somewhat a matter of luck) to get sharp night images.

    >
    > Tell me about it! My stereo goes all the way to 11.


    You've *got* to start getting your own stereo equipment. Buying
    Nigel Tufnel's used gear just doesn't add up, in more ways than one.
    [mpa!]

    "The last release from the FreeBSD 4.x stable branch, FreeBSD 4.11
    (which followed 4.8, 4.9, and 4.10), was known as the "Spinal Tap"
    release" - - http://en.wikipedia.org/wiki/Up_to_eleven
    ASAAR, Jan 23, 2007
    #11
  12. jmc

    Toby Guest

    This should not happen on a short lens like the 17-50

    Toby

    "jmc" <> wrote in message
    news:...
    > I've been noticing that on my Tamron 17-50mm lens, in manual focus mode if
    > I run the ring out to the infinity end, it goes out of focus. Infinity
    > focus is just in from the end of the ring's turn. If that makes sense...
    >
    > Is this normal? I'm new to DSLRs and their lenses. It's really annoying
    > when trying to do sky photography, makes it nearly impossible (and
    > somewhat a matter of luck) to get sharp night images.
    >
    > Thanks for any help.
    >
    > jmc
    Toby, Jan 23, 2007
    #12
  13. jmc

    jmc Guest

    Suddenly, without warning, Paul Rubin exclaimed (22-Jan-07 10:49 PM):
    > jmc <> writes:
    >> I've been noticing that on my Tamron 17-50mm lens, in manual focus
    >> mode if I run the ring out to the infinity end, it goes out of
    >> focus. Infinity focus is just in from the end of the ring's turn. If
    >> that makes sense... Is this normal?

    >
    > It's not that uncommon, and it's normal in certain types of fancy
    > lenses and telescopes, but for a random consumer lens like that 17-50
    > it means the infinity stop slightly out of adjustment.
    >
    > Anyway, it shouldn't be a real problem with normal MF technique.
    > Basically focus the lens all the way to the infinity stop (which can
    > mean slightly past actual infinity). You can develop a reflex for
    > doing that simultaneously with lifting the camera to your eye. Camera
    > makers like Nikon and Pentax make their lenses all consistent in the
    > direction of rotation towards infinity so that you can do that by
    > reflex. However they didn't all make the same choice, so clockwise
    > and counterclockwise are sometimes called "the Nikon direction" and
    > "the Pentax direction" (I'm not sure which one Canon uses).
    >
    > Once the camera is at eye level, focus away from infinity while
    > watching the finder screen. You can do this pretty quickly (go for
    > speed and smoothness rather than precision) and you will see the image
    > come into focus. Stop turning when that happens, which means you will
    > overshoot a bit. Then turn the lens in the other direction more
    > carefully, stopping just at the point of correct focus using the split
    > image prism (oh yes, you need a focusing screen with split image
    > prism, normal on MF SLR's but a special upgrade for most DSLR's, sigh).
    >
    > You should not overshoot in this second operation. Focusing is three
    > steps: 1) set lens to infinity by feel, without having to look at it;
    > 2) coarse focus, overshooting focus point; 3) precise focus, just a
    > slight adjustment to the coarse focus. You should not need to hunt
    > back and forth or otherwise mess around like beginners often do. This
    > technique takes a little bit of practice but once you get the hang of
    > it, at least on non-moving subjects you can focus almost as fast as an
    > AF system can.


    Interestingly, I do consider myself a DSLR beginner (haven't had a real
    lens since 1998 and that camera was 20 years old and full manual).

    Anyway, interestingly, this is just about the exact method I was using
    last night, 'cept by the end I could get to what looked like the correct
    focus (no split image, and very very dark) without overshooting when
    starting from "beyond infinity".

    jmc
    jmc, Jan 23, 2007
    #13
  14. jmc

    jmc Guest

    Suddenly, without warning, Dave Cohen exclaimed (23-Jan-07 2:36 AM):
    > M-M wrote:
    >> In article <>,
    >> jmc <> wrote:
    >>
    >>> Infinity focus is just in from the end of the ring's turn. If that
    >>> makes sense...

    >>
    >>
    >> Same with my Nikon lenses. I was wondering about that also.
    >>

    > I used to see that with a third party zoom on my canon slr. Surprised it
    > would happen with original lenses though.
    > Dave Cohen


    It's not an original lens, it's a Tamron 17-50mm.

    jmc
    jmc, Jan 23, 2007
    #14
  15. jmc

    jmc Guest

    Suddenly, without warning, M-M exclaimed (23-Jan-07 10:14 AM):
    > In article <ep3j42$dqs$>,
    > Paul J Gans <> wrote:
    >
    >> It is done on purpose. I believe that the autofocus mechanism
    >> has to be able to go past the best focus in order to know
    >> that that's the best focus.

    >
    >
    > This appears to be the most sensible explanation so far.
    >


    Agreed. So it's not broke after all :) Man, getting a lot of user
    errors with this new camera!

    Maybe I should put it away and just use my backup cam (coolpix 5600)

    ....

    Nah! I'm having too much fun with the Rebel! Helps that I love to
    learn new things, and this camera is that!

    jmc
    jmc, Jan 23, 2007
    #15
  16. jmc

    Colin_D Guest

    jmc wrote:
    > I've been noticing that on my Tamron 17-50mm lens, in manual focus mode
    > if I run the ring out to the infinity end, it goes out of focus.
    > Infinity focus is just in from the end of the ring's turn. If that
    > makes sense...
    >
    > Is this normal? I'm new to DSLRs and their lenses. It's really
    > annoying when trying to do sky photography, makes it nearly impossible
    > (and somewhat a matter of luck) to get sharp night images.
    >
    > Thanks for any help.
    >
    > jmc

    A zoom lens zooms. If you focus on a particular object and then alter
    the zoom, you will lose focus. Zoom lenses for still cameras aren't
    designed to maintain focus with zooming, unlike video or movie cameras,
    where the lens is required to maintain focus while zooming.

    A side effect of this is that the infinity setting will shift slightly
    depending on the zoom position. It's not a fault, it's just
    characteristic of still camera zooms. My 17-85 mm USM IS lens does it
    too - there's about a 3mm difference in the infinity position between
    the 17 and the 85 mm ends. 85 mm agrees with the mark, the 17 mm is
    about 3mm short of the mark.

    Focus carefully on a distant object in daylight and note or mark the
    position of the focus scale at the zoom setting you want to use at
    night, and use that.

    Colin D.

    --
    Posted via a free Usenet account from http://www.teranews.com
    Colin_D, Jan 23, 2007
    #16
  17. jmc

    Roy G Guest

    "Annika1980" <> wrote in message
    news:...
    >
    > jmc wrote:

    images.
    >
    > Tell me about it! My stereo goes all the way to 11.



    Oh ! No !

    There must be something wrong with mine, it only goes to 5.

    I really will have to take it back, and get it exchanged for one that goes
    to at least 10.

    Roy G
    Roy G, Jan 23, 2007
    #17
  18. Toby wrote:
    > This should not happen on a short lens like the 17-50
    >
    > Toby
    >
    > "jmc" <> wrote in message
    > news:...
    >> I've been noticing that on my Tamron 17-50mm lens, in manual focus mode if
    >> I run the ring out to the infinity end, it goes out of focus. Infinity
    >> focus is just in from the end of the ring's turn. If that makes sense...
    >>
    >> Is this normal? I'm new to DSLRs and their lenses. It's really annoying
    >> when trying to do sky photography, makes it nearly impossible (and
    >> somewhat a matter of luck) to get sharp night images.
    >>
    >> Thanks for any help.
    >>
    >> jmc

    >
    >


    I found that the only cure (on a Canon 30D) was test shots,
    checked at extreme blowup on the back viewing screen. This works,
    so long as the lens (manual setting of course) does not slip.

    Doug McDonald
    Doug McDonald, Jan 23, 2007
    #18
  19. jmc

    Mike Russell Guest

    "jmc" <> wrote in message
    news:...
    > I've been noticing that on my Tamron 17-50mm lens, in manual focus mode if
    > I run the ring out to the infinity end, it goes out of focus. Infinity
    > focus is just in from the end of the ring's turn. If that makes sense...
    >
    > Is this normal? I'm new to DSLRs and their lenses. It's really annoying
    > when trying to do sky photography, makes it nearly impossible (and
    > somewhat a matter of luck) to get sharp night images.


    Not unusual for a telephoto, because thermal expansion is a factor in
    focusing lenses with a long focal length. For a short lens though it's
    either a problem with the lens itself, as others have mentioned, or less
    likely a problem with the camera's flange focal distance. Swap lenses with
    another camera and see if the problem follows the lens or not.
    --
    Mike Russell
    www.curvemeister.com/forum/
    Mike Russell, Jan 25, 2007
    #19
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