70D - Sigma lens - Live view issue

[yogi62]

Hi guys,

Not sure if anyone has experienced the issue I have at present but I woudl be interested to recieve any feedback.

Camera is 70D and the lens is a Sigma 17-70 f2.8-4.5. If I use live-view and touch the screen to focus the lens focuses fine and looks sharp on screen. I can enlarge the focussing area for more accuracy and all looks ok. However, when I press the button half way to gain focus lock the lens moves back and forward as normal seeking focus lock. Then the camera beeps and the square turns green confirming lock.

The issue is the image is actually not in focus when the squre turns green. if I release the button the continious autofocus system again finds clear accurate focus but when I again press the button half way down it again locks out of focus.

Incidently the lens works fine in AF mode through the viewfinder

Anyone got any ideas?

regards

yogi62

[Waddizzle]

Is this the only lens that exhibits this behavior? 

Have you tried turing off AF on the lens after the initial focusing? 

[yogi62]

Thank you for your response.

In answer to your reply and the previous respondent (also thanks), I have tried the camera with both Canon lenses and another Sigma 10-20mm. The Canon lenses work flawlessly and my Sigma 10-20mm seems to work most of the time, so it appears to be isolated to the Sigma 17-70. Interestingly the Canon user manual (page 233) suggests if you want precise focussing to switch to manual mode, magnify and then take the picture. This is now my work around for the Sigma lens.

I did contact Sigma and they were willing to take a look at the camera  / lens combination (cost in the UK is £35.50p) Howver they mentioned that they did not have a firmware update for the lense / 70D combination so I have decide to stay with manual focus for live view and normal AF in viewfinder which is my main method of taking pictures.

Regards

yogi62

[ebiggs1 · Accepted solution]

It's not worth it.  Either forget about it and use it as is or buy a lens that is compatible with your camera.

[yogi62]

Answer: bought a second copy of lens 'on approval' to test and it has worked flawlessly. This the contemprary 'C' version.

Thanks for your feedback.

regards....

[ebiggs1]

I am not familiar with that Sigma but not all Sigmas support all functions of the camera.  Do real Canon lenses work as they should?  If they do the Sigma is not compatible.