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11-21-2012, 06:57 AM   #1
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Focusing Charts

I just ordered a Tamron 17-50/2.8 earlier this week, and was wondering if anyone could offer some advice on how I can test the lens to check for front/back focusing and other possible defects in a new lens? I've heard that this lens can except FF or BF and wanted to check my copy for any issues.

11-21-2012, 07:50 AM   #2
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I have a quick-n-dirty AF adjustment test that works fine for me but some people prefer the charts.

Grab a cereal box or anything else that's got a flat surface with small printing on it. Put the camera on a tripod some distance away from the cereal box, where you're not down toward the minimum focus distance.

Set the camera to the center AF point, low ISO, maximum aperture (in aperture priority) and take a picture. Note the shutter speed, then switch to manual so you can maintain same exposure settings, set the AF fine adjustment to -1, re-focus, and take another picture.

Go to review mode, and press the down arrow/flash button to bring up the review menu and choose the side-by-side comparison option. Put the two shots next to each other, and zoom in until you can see which one has the sharper text.

If the -1 adjustment one looks sharper, repeat the process with further steps out to -2, -3, etc until the pictures stop getting sharper. If the un-adjusted shot looks sharper, do the same but with positive adjustments.

Eventually you'll land on what setting gives the sharpest results. This really varies with each lens, so since the K-r only lets you set a global AF adjustment factor rather than for specific lenses, I just keep a list of AF correction factors for each of my lenses and change the AF fine adjustment when I change lenses. I use Evernote on my phone for keeping the list with me wherever I go.
11-21-2012, 09:53 AM   #3
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Here's one from a Nikon forum that I've used before. For more repeatable results there's always the LensAlign.
11-21-2012, 09:55 AM   #4
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The most important thing that I have ever realized in doing lens focus testing is:

Make sure your camera is perfectly level with the lens test image. As in - your sensor should be perfectly parallel to the image.

11-21-2012, 10:05 AM   #5
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QuoteOriginally posted by JinDesu Quote
The most important thing that I have ever realized in doing lens focus testing is:

Make sure your camera is perfectly level with the lens test image. As in - your sensor should be perfectly parallel to the image.
Very true although with a lens focus chart it should be at 45.
11-21-2012, 10:42 AM   #6
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I use this method.
AF microadjustment for the 1Ds mark III, 1D Mk3, 5D Mk2, 7D, 1D X
11-21-2012, 02:46 PM   #7
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QuoteOriginally posted by wtlwdwgn Quote
Very true although with a lens focus chart it should be at 45.
NOT!! The main problem is that scheme provides an ambiguous focus target (courtesy of the 45). The key to successful and valid testing is to only challenge one aspect of a system at a time. The LensAlign is somewhat better in that it provides a vertical focus target with a ramped scale to the side.

If you want to evaluate front/back focus without buying anything, use a flat target parallel to the sensor. Working from a tripod, lock with AF and use live view with a loupe and manual focus to confirm accuracy and direction of bias.

I personally prefer the free moire-based focus targets. With them, all you need is live view. See link on COULDBE2's comment above.


Steve

Last edited by stevebrot; 11-21-2012 at 02:57 PM.
11-21-2012, 04:00 PM   #8
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There is a free chart made by a Pentax enthusiast. It is one that I have printed out, and I'll be using it very soon because I have some incoming lenses to test.

PENTAX DSLRs: Front or Back Focusing Problems? Free test (Lens Alignment) charts for Pentax, Nikon, Canon, Sony, Olympus.

11-21-2012, 04:02 PM   #9
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I also recommend couldbe2's link. That approach has replaced all the other paper-based charts for me for a few years now.

M
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