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Does my 16-55 have an issue?

Started Feb 18, 2020 | Discussions thread
tokumeino Veteran Member • Posts: 3,175
Testing a lens for decentering
2

In my experience, tests such as https://www.lensrentals.com/blog/2012/05/testing-for-a-decentered-lens-an-old-technique-gets-a-makeover/ are better to judge centering because they are less prone to user error. So if you are afraid that your lens could be decentered, you should try it.

If you don't own such a chart, download a file and print yourself (https://commons.wikimedia.org/wiki/File:ImageTestStarJMW.pdf). On a genuine chart, the circle is like 20cm in diameter, so you can crop and print A4 on a good paper (and leave room arround the sheet when making the picture). This process is much less demanding as far as precision is concerned : alignment is not critical, and the test requires a defocus so focus is not critical as well.

All you need to watch is the small circle in the center. If blur it not perfectly even, then return the lens without question.

Bottom left is totally decentered. Bottom right is supernice (absolutely no shift in the blur pattern). Others are probably good even if top left is questionable (small shift of the black circle towards top-right direction).

Some use this technique directly with a PDF chart displayed on screen (https://yukosteel.wordpress.com/2018/06/30/bad-lens-or-optical-alignment-issue/). In that case, the whole test is a matter of seconds : why not trying ?

Very bad lens sample : you can clearly see the blur shift (or dark point shift) at different focus distances.

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