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Author Topic: Question about these results  (Read 530 times)
cometer
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« on: December 07, 2013, 02:30:31 PM »

This a comment for this page on the website
I'm an owner of EF-S 17-55 F2.8 IS USM and 70D. I'm disappointed at the results shown here, because EF-S 17-55 F2.8 IS USM is the only flagship zoom lens for APS-C DSLR and some of the other reviews have given it quite a credit as being comparable to the full-frame 24-70 F2.8 L II in optical performance.

Could it be that the poor result is due to "focal point shift", a common issue seen by many Canon lens. For example, my own EF-S 17-55 F2.8 IS USM needs a "plus 4" micro focus shift adjusted in 70D to achieve the best focusing.
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Emilie_DxOMark
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« Reply #1 on: December 17, 2013, 10:00:10 AM »

Hello,

Thanks for your feedback, it is very important because it enable us to improve/check our measurements.
In this specific case, we did many test on different samples to check our results.
 
About focusing micro adjustment, the DxOMark protocol is made to avoid such trouble: For each couple focal-aperture measured, we perform what we call a “through focus”: We shot around 40 pictures with short move on an optical rail between each picture.
We measure sharpness on each picture and we performed all measurement on the best one. This best one correspond to the best focusing position.

Best regards,

The DxOMark team
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