Educate me on AF

al4x said:
i have given it a try tonight (not ideally enough light)

however.

so far the macro L is absolutely spot on. its DoF is so narrow the only thing that is in focus is the black line
and it is perfectly in focus
it may have a tiny tiny amount of backfocus. nothing i would worry about.
the line 2mm behind target is ever so slightly more in focus than the one 2mm nearer

the new sigma is definitely back focusing in both live view and viewfinder
Click to expand...

The 120-300 is well know to have back focus issues. If it's definitely back focusing and you can't microadjust it out then you have two options. If it's the sport version then find a USB calibration device (maybe a camera shop near you), if the older OS version then you'll need to send it in to sigma for calibration. It's on their standard charge list and about £60 iirc. You'll have to send your camera as well.

Mine had the back focus issue when I first got it (bought second hand oddly so not sure how I wasn't picked up before!), sent it to sigma and it came back perfect. Well worth doing.

As DP said though, short distances are not pointless. Go out and shoot the hints with it. Something like ducks at a pond are good, that will tell you if its consistently back focusing.
 
To address the points so far..

The 35mm I can use the dock for but my 120-300mm is not the new dock friendly version

The times when focus is completely missed are the ones I can't understand.
This happens with both the sigma lenses

For the 120-300mm I mainly picked up on it at the airshow. This isn't back focus. The aircraft wouldn't be out of focus for such a minor back focus issue.
So so many shots were completely fuzzy. It's possible it's lack of contrast (the aircraft were often dark) it wasn't my shutter speed (1/800sec)
I think it's something with focusing on a moving target and me here and the added focal length difficulty
It's also a big heavy lens

The 35mm does this complete fuzzy game a bit too but there are less variables. It isn't on moving targets and obviously is an 'easy' focal length.
It's not me on this one (ie unsteady hand) as my 100mm l never does this with a shallower DoF
2 shots on high speed seem to come out one ok, one fuzzy. I am thinking is me again, but I can't think how it can happen.
 
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I think you need to reset your expectations in some respects,

To be frank, it's quite difficult to get pin-sharp shots where something like a dog is moving, it takes a lot of practice and I'm not sure a 60D would be up to it,

The second shot looks roughly in focus to me, but the IQ is very poor, possibly due to ISO 800, as high ISO in all but the best cameras tends to muddy the detail and make it look like a watercolour

The first shots it just looks like the camera hasn't locked focus, this takes practice and it takes exact knowledge of the camera, for example - before I used to go to go and photograph puffins in flight, i'd spent a few hours at the side of the road with a 300 F2.8 photographing cars going past at 60mph, and even with a 300 F2.8 and a 1DMkIII (sports body) it took a LOT of practise to get right... (I mean a lot)
 
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if its me thats fine, i did wonder. As long as its not defective kit that is the main thing. It could quite possibly be the 60Ds AF holding it back as well as me. again, if this is the case that is also fine.

there are a fair few like the second one with lower ISO.
 
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