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Forum: Pentax K-1 05-21-2016, 11:10 PM  
K1 Autofocus
Posted By Digitalis
Replies: 115
Views: 20,813
The only K mount AF lens I have in this focal length range is the Sigma 15-30mm f/3.5-5.6 and it focuses with reasonable accuracy - providing you use manually selected focus points* on the K-1. You even need to do this with the Nikon D3 with the 14-24mm f/2.8, that lens can only consistently focus with AF at infinity is through using manual AF point selection.

*preferably, one of the 3 central ones.
Forum: Pentax K-1 05-21-2016, 09:58 PM  
K1 Autofocus
Posted By Digitalis
Replies: 115
Views: 20,813
we are talking about the Pentax D-FA 15-30mm f/2.8 on the K-1 here - a completely different lens.
Forum: Pentax K-1 05-21-2016, 06:10 PM  
K1 Autofocus
Posted By Digitalis
Replies: 115
Views: 20,813
Setting the focus to infinity does not guarantee the lens will stay there, there aren't many Full format UWA lenses that are classified as parfocal, there is always some degree of focus shift. Often it is masked by the inherent depth of field with such wide lenses though the resolution of the K-1 sensor will reveal things the eyes fail to detect.
Forum: Pentax K-1 05-21-2016, 04:30 PM  
K1 Autofocus
Posted By Digitalis
Replies: 115
Views: 20,813
No shame in that.

With some of the medium format cameras I work with having only a handful of AF points, I often have to do the same.



You should also consider the possibility there is a centering defect with your copy of the lens - if it is severe enough it could indeed affect AF precision.I have had one 15-30mm f/2.8 that was de-centered. I'm currently in the process of assessing and testing my second copy, But at this point I am not haveing the difficulties you are experiencing.

In my typical usage I use AF-S, Select mode, using the center point.
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