Live view and normal focus what's the difference?

[bobkent]

Was looking at checking the Sigma 70-200 f/2.8 macro mk2 focus as it has seemed a but off. I put it on a tripod set it to ISO 100 f/2.8 and focused on some text about 30 feet away at 200mm.
If I focus as normal the text sems slightly out of focus, low contrasty. If I turn to live view zoom and focus the text comes out clearer and higher contrast.
I thought it might be the mirror vibrating so selected lock mirror. Still the same issue!
Any ideas?
I will pop up 2 pics later showing the difference.

Thanks in advance.

Oh I did this on a canon 50d and a 500d. Same results on both.
And same settings on both, centre point AF spot metering and AWB.

 

[Canon Bob]

"Normal AF" uses sensor pairs in the bottom of the mirror box to detect phase difference from each side of the aperture. Liveview uses the actual image sensor for contrast detection.

Bob

 

[bobkent]

Thanks Bob... nice name by the way

I understand what you are saying, but wish I never asked... now want to only focus with live view, as the difference was quite noticeable!!

 

[Canon Bob]

Thanks Bob... nice name by the way

I understand what you are saying, but wish I never asked... now want to only focus with live view, as the difference was quite noticeable!!

You could try the micro-adjust feature on the bodies to see if you can get the phase detect AF closer.

Bob

 

[HoppyUK]

You could try the micro-adjust feature on the bodies to see if you can get the phase detect AF closer.

Bob

That's what microadjust AF is for.

There are a couple of current threads running on just this topic.