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Old Jun 23, 2009, 11:57 AM   #1
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Default When you get a new lens...

how do go about finding out the sweet spot, or the point where it's at it's sharpest. Or do you even do that? And what is the process when you see a tree for example and you want to shoot it. what steps do you take? I know this is an in depth question, but any help is appreciated.
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Old Jun 23, 2009, 12:25 PM   #2
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Actually, before I buy a lens, I review the test results to see what the lens' limitations are. SLRGear.com and PhotoZone.de are excellent sources for that kind of info.


If you want to do some testing on your own, there are a variety of ways you can do it. I've done all of the following:
  • Created a test pattern in Visio, and shoot it with different lenses at different apertures.
  • Shoot a brick wall with different lenses at different apertures. This has the added benefit of showing pincushion and barrel distortion, but sharpness is harder to judge than with a good test pattern.
  • Shoot a sunset through trees with no leaves. Of course, this can only be done in the winter, which presents its own set of difficulties, but it is a great way to see the relative sharpness from one aperture to the next, and anywhere in the frame.
All, of course were performed with the camera mounted on a tripod.

Last edited by TCav; Jun 23, 2009 at 9:01 PM.
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Old Jun 23, 2009, 5:57 PM   #3
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And remember to turn off SSS when using a tripod.
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Old Jun 23, 2009, 9:37 PM   #4
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Here are some examples of what I mean.

The first is a reduction of a shot using a KM 18-200 at 35mm and f/5.6.

The second is a reduction of a shot using a Beercan at 200mm and f/5.6.

The third is a 100% crop of a shot using a Minolta 135/2.8 at f/8.0
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Last edited by TCav; Jun 23, 2009 at 9:48 PM.
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Old Jun 23, 2009, 11:28 PM   #5
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Thanks as always for the info. What is meant by 100% crop?
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Old Jun 24, 2009, 5:55 AM   #6
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Quote:
Originally Posted by antonlmo View Post
Thanks as always for the info. What is meant by 100% crop?
In the case of the above image of the trees at sunset, it's a 640x426 image cropped from within the original larger image. Each pixel in the 100% crop is a single pixel in the original.

I maintain the original, full size image for purposes of comparison; I just cropped a 640x426 section from the center so I could post it here.

This is a reduced version of the full size RAW image:
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Last edited by TCav; Jun 24, 2009 at 8:14 AM.
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