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05-16-2012, 03:27 PM   #1
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Aperture not fully adjustable?

I realized something quite annoying, with my kit DA 18-55 lens and K-x set on Av, depending on where I am focusing the aperture is not fully adjustable to the max and min stops that I know the lens is capable of. Sometimes it stops as low as f40, other times at f32, same thing with max. sometimes it is f4 others times only f5.6. Any explanation or way to make it fully adjustable?

05-16-2012, 03:31 PM   #2

Join Date: Oct 2011
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That's why it is listed as 3.5-5.6. The max aperture changes with the zoom -- at 18mm you can open to f/3.5, but at 55mm you can only go to f/5.6. In the middle, you get the middle range. This is normal for most zoom lenses, except for "fixed aperture" zooms, which are generally higher quality and more expensive.
05-16-2012, 03:35 PM - 1 Like   #3
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The DA18-55/3.5-5.6 has different aperture limits at different focal lengths. At 18mm the range is f/3.5-22. At 55mm the range is f/5.6-40. An f-stop is a ratio of the aperture diameter to the focal length. As the focal length changes, the ratio changes. Does this make sense?
05-16-2012, 04:14 PM   #4
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Original Poster
aaahhh, ok that makes sense. I was wondering why it was listed like that. Thanks guys!


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