[Surrey Sam]

That's good news Gerry; I have been following this thread quite keenly as another 100-400 user. I've had my example for some 14 months now and to be quite frank I have not been blown away with its results, this has mainly been down to images been a fraction soft in my minds eye. I have always put this down to user error and have been improving my technique for using the lens, as after all it is a 1k piece of L glass which should deliver good results!

Unfortunately for me I've never had reason to doubt its performance, as it was my first L lens and have never had anything to compare it with. This was until recently where I have now been able to add a 24-105 L lens to my collection and that has been a joy to use. I have now been able to get images that give me the "wow, did I really take that" factor; so I've turned to my 100-400 accusingly, thinking that perhaps it's not firing on all cylinders.

I think that I've decided in my own mind to send it off and get it checked out, it's a shame that I can't do it under a warranty now, so can only hope that it's a reasonable cost to tune the lens and get it working as it should. Here is a 100% raw crop saved to a tiff format to give an example of what results I'm getting, you will need to click on the bar at the top of the photo for the full size. The Nuthatch was still and the camera mounted to a monopod.

All critique is welcomed and I’d especially like to hear anyone’s experience in getting a lens calibrated and an indication on what sort of cost to do this work?

400mm, 1/160sec, F/7.1, ISO 800.