IF - Internal Focusing....???


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kevyan

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Jan 5, 2005
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#1
Hi all,

I am rather puzzled by my Tamron SP AF17-50mm F/2.8 XR Di II LD Aspherical [IF].

Isn't IF means internal focusing, where is does not change the physical length of the lens?

Why is it that when I zoom the lens, it extended the physical length of the lens? :dunno:

Or does it means that it doesn't change the length when focusing? I blur liao.... any sifu can help enlighten me?
 

Rashkae

Senior Member
Nov 28, 2005
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#2
Hi all,

I am rather puzzled by my Tamron SP AF17-50mm F/2.8 XR Di II LD Aspherical [IF].

Isn't IF means internal focusing, where is does not change the physical length of the lens?

Why is it that when I zoom the lens, it extended the physical length of the lens? :dunno:

Or does it means that it doesn't change the length when focusing? I blur liao.... any sifu can help enlighten me?
Zoom is different from focus.
 

flipfreak

Senior Member
Nov 26, 2007
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www.rogerchua.com
#3
internal focussing refers to the length of the lens doesnt change during focusing. some of the newer lens extend when it is focusing. when u are zooming in, its zoom, not focusing.
 

kevyan

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Jan 5, 2005
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#4
Ah... okay.... I koo koo.... not sure, so I ask all the sifu here.... so paiseh....:embrass:

Thank you very much.

internal focussing refers to the length of the lens doesnt change during focusing. some of the newer lens extend when it is focusing. when u are zooming in, its zoom, not focusing.
 

senray

New Member
Nov 25, 2006
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www.picturesque.sg
#5
Hi all,

I am rather puzzled by my Tamron SP AF17-50mm F/2.8 XR Di II LD Aspherical [IF].

Isn't IF means internal focusing, where is does not change the physical length of the lens?
....
Or does it means that it doesn't change the length when focusing? I blur liao.... any sifu can help enlighten me?
"it means that it doesn't change the length when focusing"

-> you actually just answered your question. =)
 

senray

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Nov 25, 2006
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www.picturesque.sg
#8
no lah! not to embarass you or anything, I don't even know what all those terms like "IF", "AF" last time too. Once you get the hang of it, it is as easy as ABC.

Don't we all? =)
 

giantcanopy

Senior Member
Feb 11, 2007
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#9
Internal Focusing. A conventional double helicoid focusing system requires that all lens groups be moved by the lens barrel to either the front or rear during focusing. This mechanism is not only complicated but bulky, more so in the case of telephoto lenses where the extra physical length of the lens requires the use of a heavier gauge metal with a consequent increase in size and weight. In addition, a change in the length of the lens when focusing results in unbalanced hand held shooting.

To remedy this situation, Nikon developed the Internal Focusing (IF) system. With IF, only the internal small lens group shifts during focusing with no change in the lens' physical length, permitting more compact, lightweight construction and a closer minimum focusing distance for telephoto lenses. Additional benefits include faster focusing and a reduced diameter of the focusing ring due to a simplified focusing mechanism.


From the encyclopedic mir website link
 

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