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Old Jul 9, 2009, 1:25 PM   #1
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Default Lens uses.

I'm picking up quite a bit just be reading here. I do have a question about lenses. When do you use a particular lense? My camera came with two: 18-55mm standard zoom lens and 55-200mm telephoto lens.
What can I do with one (other than long zoom) that I can't with the other? I'm new at this, so I hope this dosen't sound too dumb.
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Old Jul 9, 2009, 2:04 PM   #2
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with those two examples, the difference really comes down to zoom and framing. If you're indoors in a 15' x 10' room, that 55-200mm lens is going to be too tight to take photos. Standing outside and want to take photos of a duck on the pond, you could always swim out and use the 18-55 or stand comfortably on the shore and take the shot from there. Conversely if you want a landscape shot with the whole pond in it you'll find that 55-200mm isn't wide enough and backing up until it all fits in the frame gives a slightly different (flatter) perspective than using 18mm up close.

Also, focal length of the lens alters depth-of-field (DOF). DOF refers to how much of an image in front and behind the plane of focus appears to be in focus. If you take a photo of a person using 18mm at f5.6 and then switch lenses and use 200mm at f5.6 and back away until the person is filling the same amount of the frame as they were at 18mm you'll find the background is less in focus at 200mm than the shot at 18mm.

With other lenses, there are other important differences:
Some lenses are sharper than others
Some are better built
Some have a better maximum aperture (lower f-number)
The blade design on lenses renders different out-of-focus backgrounds - so two different lenses at 200mm f4.0 could produce photos where the out-of-focus background looks different (the 'quality' of such a background is referred to as 'bokeh')
Some lenses, based on their design, focus faster than others
Some lenses have a better build quality
Some lenses have the capability to focus closer to a subject and produce an image closer to actual size (1:1 ratio of a true macro lens).

So, there are a lot of differences from one lens to another but in the two lenses you specified, sharpness, build quality and max aperture are virtually the same. The difference is mainly in which focal lengths they provide.
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Old Jul 9, 2009, 2:21 PM   #3
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Thank you John. That is very helpful.
Right now I'm heading to a park to look for subjects. I guess I need to take both lenses in order to be prepared.
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