How to test a new (Ultra Wide) lens - Sigma 8-16mm?

Started Nov 14, 2012 | Discussions thread
Leonard Shepherd
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Re: Yes - and no
In reply to scrane, Nov 16, 2012

scrane wrote:

I have never seen a camera that can't focus on a book's spine.

There is a big difference between camera AF detecting something, and detecting something at the distance you intended.

Book cases often have books at slightly different distances with different size letting on the book spines. Either can sometimes cause poor focus accuracy - as indicated in the section in camera instruction books on getting good results using AF.

Phase detect AF detects contrast differences. If there is better contrast difference near the centre of the viewfinder mark, sometimes AF focuses off centre instead of on what is at the centre of the viewfinder mark. While this may not often happen when it does it is not due to a camera body or lens fault.

As the OP wants to be sure the new lens does not have a fault there seems no point in using targets which might result in poor focus accuracy with a good lens.

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Leonard Shepherd
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