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Author Topic: Question about these results  (Read 2338 times)

Offline cometer

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Question about these results
« 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.

Offline Emilie_DxOMark

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Re: Question about these results
« Reply #1 on: December 17, 2013, 10:00:10 am »

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

Offline Igor Pogorelyy

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Re: Question about these results
« Reply #2 on: March 26, 2017, 03:20:52 pm »
Maybe the results of testing this lens can be better if dxo add a measurements at f/4, where the 17-55 is sharper. Not quite as sharp as 24-70 mk2 though. Sorry for my English.

Offline Renarik

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Re: Question about these results
« Reply #3 on: April 05, 2017, 04:55:44 am »
You might want to see my response on a potentially related question, at:,5188.msg9563.html#msg9563.

It's very difficult for any lens to achieve the same resolution on an APS-C sensor as on a full frame sensor, just a smaller area on which to focus the image. That smaller area means the tolerances in the lens must be much tighter on APS-C than on full frame to achieve the same result. I go into more detail at the link above.

This may not be the only reason for a disappointing rating, but it may help explain why you're seeing some of those differences.

Good luck!