F.O.A. Scottthehat; Focus tests as requested.

Here they are.
No PP, all the same ISO.
Tripod Mounted.
2 second timer.
SR OFF.

F5.6
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus256.jpg[/IMG]

F6.3
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus263.jpg[/IMG]

F7.1
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus271.jpg[/IMG]

F8
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus280.jpg[/IMG]

F9
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus290.jpg[/IMG]

F5.6
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus56.jpg[/IMG]

F6.3
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus63.jpg[/IMG]

F7.1
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus71.jpg[/IMG]

F8
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus80.jpg[/IMG]

F9
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus90.jpg[/IMG]

to be honest graig it doesn,t look bad but its not brill. not as sharp as i would like,f8 and f9 is were you wanna try get it really when shooting as its alot shaper, and i see you have had no real luck with the focus charts a could not get nothing at all, it would be nice to see a crop of each on the cereal box, of the hm the queen bit,

have you tried adjust the front focus, also how did you do the focus chart test as to me i looks like it has major front focus,

I havent tried the focus adjuster as according to reports if you adjust for front or back focus @ 400mm you get major front or back at the 120-250mm range.

Just did the focus test as they said on the blog.
Flat table, tripod, AF, focus on the cross.

Heres the crops.
These look woefull at all apertures.

f5.6
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus256-1.jpg[/IMG]

f6.3
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus263-1.jpg[/IMG]

f7.1
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus271-1.jpg[/IMG]

f8
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus280-1.jpg[/IMG]

f9
[IMG]http://i271.photobucket.com/albums/jj132/CraigF1969/private/focus290-1.jpg[/IMG]

You should try Yvon Bourque's newer focus chart. There is too much "crap" on this one to accurately figure out where the camera has locked focus. Here is where you can find it:
link

The last shots look "woeful" because it appears you have a quite bad front focussing issue. You will not see this in an image of a flat subject that is parallel with the sensor's focal plane. It's obvious in the shots of the chart though.

Yes, any adjustment for focus issues at one end of the zoom range might adversely affect focussing at the other end. I think we have to live with that.

Primes are the only real answer to this problem, or very expensive zooms manufactured to tighter designs and tolerences.

Many modern zooms are not zooms at all but varifocals. They do not hold their focus when zoomed. Very expensive ones do, very cheap ones definitely don't, but there's a whole grey area between those two extremes where some hold focus better than others.

Try it. Manually focus very precisely on something and then zoom in and see if it doesn't blur instantly.

That's true John but I've assumed Craig has refocussed at the different lengths of zoom for his tests.

The tests were all just done @ the 400mm for the time being.

The comment you made Mannesty above is not entirely true as Sigma have fixed this on lots of occasions for others and when i spoke to them last week about the focus speed also they commented they had resolved that issue and thats when they tried to lay the fault with the camera.
On that occasion they could have been correct as the camera had a fault and was returned.
I will try the focus adjustment and see if there is a marked improvement.

I realise its not a very expensive zoom John but i would still have expected a lot better from a £600 lens.

hi craig try this focus chart, if its has major front focus as it looks like it has in the first chart pics the k20 will only adjust + or -10 and yours looks a long way out, which will the prolem those pics are terrible,

Hi Craig, I don't know if you have software for comparing shots or not.
The FREE Farstone Viewer lets you compare two at a time and will also
smooth the screen when you zoom to say 200%. I can't see a way of
capturing the screen other than pressing "Print Screen" and then
pasting into MS Paint or a graphics editor.

http://www.faststone.org/FSViewerDetail.htm

It's hard to compare one lens on it's own. Try to take the same sized
photo with another lens. i.e. Fill the screen with the Box take with
lens 1. Change lens to No. 2 Move tripod to fill screen and take
another shot. Compare the two shots.

shim

I would say it was an expensive Zoom


shim

Its very expensive to me also but i am not going to compare it to a 3 grand lens for comparison.
I will try some more tests as its very overcast today and i wont be going out to shoot.