K5's two outer most AF points

Hi guys,

Finally got hold of my Sigma 30mm 1.4 yesterday (had to collect it from the wrong address they sent it to!) and took a few photos @1.4 using the two outer most AF points, and got crazy front focus - around 10-20cm!

However the lens is fine with the k5's centre 9 AF points and other lenses (slower ones, e.g. 3.5-5.6 kit lenses) are fine with the outer ones.

So I'm guessing that the K5's two outer most points aren't 'sensitive enough' for use with f1.4 glass?

The two outer points only recognise contrast flowing horizontally, the inner 9 points recognise it in both horizontal and vertical directions. When you use the outer points they require a nice strong line to run across them or they get a bit confused (in my experience). Once you know what they're looking for to lock onto you'll find they can be just as accurate as the cross points (albeit 50% less versatile).

I noticed a problem with a DA21 I got when I was in the UK last. The lens isn't a great copy - with IQ weaker on the right hand side. Using the focus points on that side (both the furthest right, but also the top right one) produced very variable results, with the focus often way off. Could the performance of a lens combine with the behaviour of the outer points as described by Hefty combine to have this effect? I haven't had the same problem with any other lens.

Re. the lens more plaudits to Chris at SRS as - despite getting the lens some months back - as it's in perfect condition he's agreed to swap the lens with another copy when I'm in the UK in August. One more reason to shop at SRS.

i guess its possible. I heard that there is variation between different lenses and different cameras in terms of AF accuracy and how they are set up in factory, and differences in factory tolerances in regards to AF.

Strange, no matter what I do, my k5's 2 outer points just don't like f1.4, though I haven't been able to try any other lenses to confirm this

With f/1.4 you can also have a problem with aberration of the lens. maybe that's it?
In the center it's mostly well controlled but it gets worst on the edges.

The resolution and contrast on the 30 f/1.4 on the edges and corners is known to be poor. Those focusing points may be unusable due to the nature of the lens.