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Old Apr 30, 2009, 9:06 PM   #11
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Shari wrote:
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John, my lense is 3.5 - 5.6. Would I be opening up to 3.5 when in A mode?

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Shari - it's only capable of 3.5 when it's at it's widest zoom. Somewhere between 18mm and 200mm the widest value it will allow is 5.6. Unfortunately lens specifications don't tell you at what focal length that occurs. You'll have to experiment.
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Old Apr 30, 2009, 11:08 PM   #12
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Thanks John - I think I have got it!
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Old May 5, 2009, 3:45 PM   #13
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This is a handy calculator that might help:
http://www.dofmaster.com/dofjs.html

Throw in 200mm for your focal length, f5.6 for your aperture and I put in 20 feet as your distance from subject.

The calculator says that the image will be sharp from 19.7 feet to 20.3 feet from you (a depth of field of about 8 inches). Anything falling outside of these two limits will appear out of focus.

If you changed the distance to 10 feet (leaving the other values the same) the depth of field becomes about 2 inches (with slightly more than half behind the point of focus and the rest in front)

With practice you'll get used to your lens and how deep the depth of field gets as you focus on subjects farther from you and how shallow it gets when you focus on subjects nearer to you.

Edit:
I should also mention that if you return to your 20 foot distance from subject and switch instead to f11, the depth of field becomes 16 inches, and at f22, 32 inches (with slightly more than half behind the subject and the rest in front)
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Old May 27, 2009, 11:48 PM   #14
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Stand a few feet away from your subject. Zoom in, put your focus point on the subject, half press, shoot and voila..clear subject with blurred background. The key though for me, not sure if anyone mentioned it, was the importance of focus point on subjects. on portraits, i stand a few feet back, zoom in, put the focus point on the eyes, half press and shoot. this was using my 18-105VR lens on my D90 and single point focus aimed at the eyes. Using my uncles 28mm 1.4 was a different story though...i set aperture to 1.4 or 1.8 compose, focus point on the eyes and wow, unbelievable pics...
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Old May 31, 2009, 11:33 PM   #15
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Quote:
Originally Posted by Shari View Post
John, my lense is 3.5 - 5.6. Would I be opening up to 3.5 when in A mode?

Thanks
Shari, the 18-200mm has a varable aperture, depending on focal length.

So at 18mm, it is F3.5, while at 200mm it's F5.6
That's because the aperture is the ratio of the focal length to the effective opening at the front of the lens. The longer the focal length, the larger the F number becomes. (generally, as there are some constant aperture lenses)

What this means for you is that at 200mm, (where you will try to make depth of field smaller on your flowers), the minimum aperture is F5.6, so you can't reduce this to F3.5 Just use the lowest in A mode which will be F5.6 at 200mm
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