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Thread: Focus to infinity ?

  1. #1
    Member HHenrYY's Avatar
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    Default Focus to infinity ?

    What does that mean ?
    and what does it do?

    and how can i do that with a Nikon D90 with 18-105mm kit lens ?

    Thanks in advance !

  2. #2

    Default Re: Focus to infinity ?

    Look at your lens. Switch to manual focus. Then set the lens to infinity.

    It's really not rocket science.
    Alpha

  3. #3

    Default Re: Focus to infinity ?

    Oh... and google is your friend too.

    http://www.google.com.sg/search?q=ho...ient=firefox-a
    Alpha

  4. #4
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    Default Re: Focus to infinity ?

    On lens without the infinity sign indicator, on AF mode, AF on the furthest object (i.e. something on the horizon), not really at inifinity but it's close enough. Switch to MF and shoot away at infinity focusing.

  5. #5
    Member HHenrYY's Avatar
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    Default Re: Focus to infinity ?

    so simply / noobly put it ,
    it's focus at the furthest subject the lens can focus ?

  6. #6

    Default Re: Focus to infinity ?

    Rather, the subject is further than your lens can focus on.
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  7. #7
    Member HHenrYY's Avatar
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    Default Re: Focus to infinity ?

    hmmm .
    so if i zoom out all the way, 105mm ,
    and focus it. does that means that i have near to / focus to infinity already?

  8. #8

    Default Re: Focus to infinity ?

    I've heard that Nikon lenses can focus more than infinity..don't really know what that means though...

  9. #9

    Default Re: Focus to infinity ?

    Quote Originally Posted by HHenrYY View Post
    hmmm .
    so if i zoom out all the way, 105mm ,
    and focus it. does that means that i have near to / focus to infinity already?
    It has nothing to do with your focal length (how far you "zoom").
    Alpha

  10. #10

    Default Re: Focus to infinity ?

    Quote Originally Posted by gnohz View Post
    I've heard that Nikon lenses can focus more than infinity..don't really know what that means though...
    In optical terms:
    light from a point source diverges
    if that object is sufficiently far away (virtual infinity), the separate light rays from it appear parallel
    for objects closer than infinity, the rays are divergent to some extent
    'beyond infinity' implies that light rays from a point source are converging on the lens, which doesn't happen in the real world

    I believe most lenses can be adjusted to focus 'beyond infinity' -- they are usually adjusted so that infinity is at the max end stop. There doesn't seem to be a reason to focus 'beyond infinity', not for normal DSLR lenses anyway.
    I'm not sure if it's necessary for IR photos (dun think so). Manual lenses used to have a different focus index for IR.

  11. #11
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    Default Re: Focus to infinity ?

    Quote Originally Posted by HHenrYY View Post
    What does that mean ?
    and what does it do?

    and how can i do that with a Nikon D90 with 18-105mm kit lens ?

    Thanks in advance !
    Optically, every lens has exactly one plane of focus, a fixed (finite) distance from the lens. Technically speaking, no lens can focus at infinity. The area in front and behind that focus plane deemed to be "acceptably sharp" (but not in perfect focus) is called the depth of field. The "acceptably sharp" area in front of the focal plane is the front depth of field, the one behind the plane is the rear depth of field. As the focal plane moves away from the lens (ie, lens focuses further away) the rear depth of field increases rapidly. Beyond a certain subject distance, everything from the focal plane "to infinity" is considered acceptably sharp, hence the lens is considered "focused to infinity". That focusing distance is also known as the lens' hyperfocal distance.

    "Beyond infinity" is built in to allow the lens to focus "to infinity" in temperature extremes when the lens contracts or expands.

    HTH

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