Help regarding the focusing issue T2i.

mohsinmehraj

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Sorry if i posted my thread in the wrong place.

I got a 550d recently and i am facing one of the strange focusing problems.
I will try to describe it here.
When i try to shoot a subject using a viewfinder the picture always front focuses, as in the picture is not clear or sharp.
But as soon as i turn the live view on the pictures is 100% sharp and crisp.
Same settings are used in both modes.
This is frustrating me a lot
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Will greatly appreciate any help i can get.
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Thank you
 
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mohsinmehraj

mohsinmehraj

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I will keep posted what happens, i put the camera away for repairs. lets see what happens.
I was about to throw the camera in toilet for doing this to me.
Thank you Hukim for the fast reply.

Pleace
 

TCampbell

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When you switch from viewfinder to live view you actually switch focusing "systems". The camera has two completely independent focusing systems.

In normal mode (when you use the viewfinder) the mirror is down. Part of the mirror is semi-transparent and reflects light downward into the floor of the camera while most of the light is bounced up into the viewfinder in the roof of the camera. The "phase detection" auto-focus sensors are in the floor. The use a split-prism to take a bit of the image out of phase. When the two halves of the image align (in the sensor) then the camera has achieved focus for that point.

When you use live-view, the mirror has to swing up so that the sensor can see through the lens. This means there's no longer a mirror to bounce light downward into the phase-detect auto-focus sensors. So the camera has to switch to "contrast detection" auto-focus which is the same system that a point & shoot camera would use. Since that focus is happening by maximizing contrast along an edge in the image but it's doing this directly ON the imaging sensor (the very same sensor that's going to take the image when you shoot) the focus is always perfect.

If your phase-detect focus can't be trusted you probably need to send the camera to Canon for service. BUT... before you do... does this happen with EVERY lens you own? It's actually possible to have a lens problem such that one lens has the problem and another does not.

See: LensRentals.com - "This lens is soft" and other myths
 

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