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Thread: What does IF stand for in a lens?

  1. #1

    Default What does IF stand for in a lens?

    The Tamron 28-200mm (3.5-5.6) lens had IF written on it. What does it stand for and what is its significance?

  2. #2

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    Usually means "Internal Focusing", that is to say the lens does not move in and out (lengthen and shorten) when focusing.

  3. #3

    Default

    I see. Thank you.

  4. #4

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    Originally posted by StreetShooter
    Usually means "Internal Focusing", that is to say the lens does not move in and out (lengthen and shorten) when focusing.
    well
    this may sounds a bit confusing cos zoom lens lengthens and shortens in focal length but can have internal focusing too

    it's more abt how the inner elements of the lens operate when focus
    [Focusing is performed by moving one or more lens groups positioned between the front lens group and the diaphragm. ]

    to noe whether if is internal or external focusing lens, observe the front element/glass- if it doesnt rotates, then it's using internal focusing

    most internal focusing lens have distance scales( eg.0.5m-infinity) marked near the lens mount

    hope it helps

  5. #5

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    Originally posted by xmen1977
    well
    this may sounds a bit confusing cos zoom lens lengthens and shortens in focal length but can have internal focusing too
    let's confuse this even more....

    you can have a zoom lens that does not extend during zooming or focusing.

  6. #6
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    Default

    Originally posted by mysteriousjimmy
    let's confuse this even more....

    you can have a zoom lens that does not extend during zooming or focusing.
    yes. classic well know poplular example would be the 80-200 nikon lenses most generatations...

  7. #7

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    OK the cheapest consumer zoom lenses have variable zoom lengths and non-internal focusing. They basically consist of 2 concentric tubes. This means that when you zoom, the lens either lengthens or shortens. And when you focus, the front element will rotate.

    The disadvantages are that

    1. With a rotating front element, use of polarizing lenses will be affected, because the polarizer needs to be at a particular orientation to work best. If changing the focus point causes it to rotate, this can be a big headache. Internal focusing takes care of this problem.

    2. With a lens that changes length, every time you zoom, air will be sucked into or pushed out of the lens. This will be accompanied by dust, of course, which means that over the long term, dust will invariably accumulate inside these types of lenses. A fixed length zoom (such as Canon's 70-200 f2.8L) remains the same length no matter the zoom length, so will not have that problem.

    Most if not all fixed-length zooms will be internally focusing, but the opposite may not be true - you may have variable-length but internal focusing lenses.

    Hope that clears up some of the confusion.

  8. #8

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    wow, the sharing by streetshooter is really very enlightening. Now I understand why my Tamron lens didn't give me problems when I was shooting with my polariser.

    This also means when I buy my lenses in the future, I'll have another thing to look out for and compare against.

  9. #9

    Default

    Originally posted by yeocolin
    ....
    This also means when I buy my lenses in the future, I'll have another thing to look out for and compare against.
    but this means you will be paying a lot more, as these lens are more expensive to manufacture, than the push-pull zoom lens, and offer better protection in the long run.

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