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07-30-2010, 03:59 PM   #1
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60-250mm f/4 does zoom out

I thought that the term 'IF' ment internal focus therefore the lens wouldn't extend zooming out but i see that this is still the case with this Pentax 60-250mm f/4

Why is it so ?

07-30-2010, 04:07 PM   #2
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Focus is not the same as zoom.
07-30-2010, 04:09 PM   #3
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QuoteOriginally posted by Jodokast96 Quote
Focus is not the same as zoom.
Whats the term for internal zoom then ?
07-30-2010, 04:18 PM   #4
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The 60-250 is not an internal zoom. The only one that IS is the 50-135 (in the SDM DA* line). Internal focus means the front element (for all practical purposes) won't rotate when the lens is focused. That becomes important when you are using something like a polarizer or a graduated filter (such as an ND).



07-30-2010, 04:49 PM   #5
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QuoteOriginally posted by JeffJS Quote
Internal focus means the front element (for all practical purposes) won't rotate when the lens is focused
It also means that air isn't being pulled into and pushed out of the lens, and that dust and moisture in the front wont be distributed inside the lens when retracted.

Neither of these should be an issue with a weather/dust sealed lens. I've not heard of any issues with people having dust inside their 60-250.
07-30-2010, 08:12 PM   #6
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QuoteOriginally posted by JeffJS Quote
The 60-250 is not an internal zoom. The only one that IS is the 50-135 (in the SDM DA* line). Internal focus means the front element (for all practical purposes) won't rotate when the lens is focused. That becomes important when you are using something like a polarizer or a graduated filter (such as an ND).

Not quite true. None of my non-internal focus lenses have rotating front element.
07-30-2010, 08:16 PM   #7
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QuoteOriginally posted by scorpioh Quote
Not quite true. None of my non-internal focus lenses have rotating front element.
So what does that have to do with the subject of internal focus and internal zoom? IOW, What did I say that is not quite true? The front of my Tamron 70-300 both extends and rotates when focused. A Non IF lens.

07-30-2010, 08:25 PM - 1 Like   #8
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An IF lens will not extend or rotate when focusing. A non-IF lens will extend, but may or may not rotate.

07-31-2010, 12:08 PM   #9
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QuoteOriginally posted by JeffJS Quote
The 60-250 is not an internal zoom. The only one that IS is the 50-135 (in the SDM DA* line). Internal focus means the front element (for all practical purposes) won't rotate when the lens is focused. That becomes important when you are using something like a polarizer or a graduated filter (such as an ND).

exactly,internal focus is not equivalent with internal zoom.
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