F3.5 - 5.5 What does this means?


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hyori

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Mar 14, 2007
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#1
I know that the max aperture is F3.5 but why the range?? can someone clarify my doubts.
 

lamergod

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Feb 9, 2009
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#2
When you zoom,the aperture get's higher as you zoom to the most tele end of the lens.So example a 18-55 lens,at `18mm it will be at f3.5 while at 55mm it will be at f5.6
 

IWONDER

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Jul 18, 2009
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#3
I know that the max aperture is F3.5 but why the range?? can someone clarify my doubts.
example:

nikkor 18-70 f3.5-4.5

it's mean when it is 18mm, maximum aperture will be f3.5,
when it's reach 70mm, maximum aperture will be only 4.5. it cannot get f3.5 in 70mm
 

hongwen37

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May 19, 2009
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Hougang, Singapore
#5
I know that the max aperture is F3.5 but why the range?? can someone clarify my doubts.

You still havent read up on the manual or other photography notes?

The maximum aperture is f3.5 at the smallest focal length... But when you zoom in to the max, the maximum aperture becomes f5.5...
 

zac08

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Feb 21, 2005
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#6
I know that the max aperture is F3.5 but why the range?? can someone clarify my doubts.
Very simple. This lens has a fixed diameter over a focal range. And aperture is based on the lens diameter to the focal length. Thus at the wider focal length, the aperture is f3.5 ratio based on the aperture diameter to the lens focal length. And NOW when you zoom in, the aperture size is still the same but the ratio to the focal length has changed and now gives you a aperture of f5.5 instead.

Those higher end lenses with fixed aperture has a varying aperture size which adjusts itself to give a constant aperture ratio even at the longer focal lengths, and this is more difficult and more expensive. :)
 

hyori

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Mar 14, 2007
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#7
i see thanks! i understand now
 

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