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I bought my 70d and the Tamron SP AF 17-50mm F/2.8 VC. I noticed that I don't have focus when I use the viewfinder but when I use the live view there is no problem at all.

Someone might come across it as well? Is there a solution or maybe I need to replace the lens ?

thank you.

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    If you can focus with the live view and/or the viewfinder, the lens works fine. Are you sure of your camera settings ? What mode are you using (and which settings) ? Some 70d have been reported to have difficulties focusing with large aperture (f3.5 and lower). Have you read the manual ? Can you describe how you are using your 70d ? Have you tried with an other lens ? – Olivier Aug 8 '15 at 12:50
  • @Olivier Thanks for your comment. I use manually mod and when I use a large aperture I having this problem,I try with the 50 f1.8 and the canon 18-135 and there is no problem. I will be happy if you can give me some solution – user3165740 Aug 9 '15 at 7:27
  • Are you saying it doesn't focus at all through the viewfinder? Or that the focus is not as accurate as Live View? Those are two completely different scenarios. – Michael C Aug 9 '15 at 17:38
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Without more details about what shooting modes and settings you have selected, your question doesn't give us very much to go on.

The 70D is a highly configurable camera and with some combinations of settings selected the behavior you describe would be as expected. It is possible that via certain custom settings options the AF has been disabled with a half press of the shutter button and requires you to use the AF-ON button on the back of the camera. It is also possible that via other custom settings the function of the AF-ON button has been reassigned to something else. If you are not intimately familiar with the various settings and menus of the 70D then perhaps you should try to reset the camera to the default factory settings and see if that solves you problem.

  • Thank you for your response. I have this problem when I use a large aperture f2.8 but only f2.8, but other lens like the canon 50 f1.8 work fine. I will be happy if you have a to this problem – user3165740 Aug 9 '15 at 7:32
  • f/1.8 is over twice as large as f/2.8. – Michael C Aug 9 '15 at 7:33
  • Yes I know but with the canon 50 f1.8 there is no problem but the tamron 17-50 f2.8 there is a problem ? why ? – user3165740 Aug 9 '15 at 7:44
  • You can add that it works fine with the 50 f1.8 in your question. I don't know how the Tamron works, but the answer may be the 70d autofocus and how it works with live view and viewfinder (details here : imaging-resource.com/news/2014/02/27/…) . Sometime my couple 7d/Tokina 116 won't focus with viewfinder and work fine with live view. Are you using AF point ? – Olivier Aug 9 '15 at 8:16
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Try Calibrating the Diopter of Your Camera to see if that helps. Since having the Diopter not calibrated may make the lens look out of focus.

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