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10-17-2014, 07:40 PM   #1
Pentaxian




Join Date: Apr 2013
Location: Brisbane, Australia
Posts: 626
FA 80-160mm focus shift

Hi,

I received a FA 80-160 this week and have done my initial testing on it, here are my comments.

When focussing at or near infinity for landscape, if I use auto focus with the mirror and AF module at f/11- f/16 the results are sharp.

If I use live view auto focus, the results are soft at f/11.

If I use live view and zoom in to 16x, then manual focus for best sharpness, then take the shot, the results are soft at f/11. (Manual focus is wide open here at f:4.5)

If I use live view, set aperture to f11, hold down the DOF Preview button, then manual focus for best sharpness, I get a perfectly sharp image. (Manual focus while stopped down to shooting aperture)

Having noted the difference on the focus distance scale on the lens between wide open and stopped down focussing, the focus distance is closer when it is stopped down to focus.

This would appear to me to be a focus shift issue, where the lens changes the point off focus based on aperture.

The only problem with this is that the auto focus off the AF module appears to be accurate.

Anybody care to chime in with their experience or comments?

Scott

10-18-2014, 04:32 AM   #2
Pentaxian




Join Date: May 2011
Location: All over the place
Posts: 2,581
I have the same lens, so will see what mine does
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645d, 645z, aperture, auto, camera, distance, f/11, fa 80-160mm focus, focus, lens, medium format, results, shift, view
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