My Canon 600D's autofocus is not working at all when using the view finder.
When I use it in live-view mode the autofocus works fine.
I tried to google but could not find anything concrete.
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Autofocus in life view and through the viewfinder use different technologies. In live view, the camera tries to get the best contrast for the image. The viewfinder AF uses the phase detection technology which includes special hardware in your camera.
If the viewfinder-AF does not work, you may have a hardware issue with your camera. Or you may have put your lens in manual mode (well I suppose, this would also disable AF in live-view).
Your dealer could help you in diagnosing the problem.