A Canon Rumors reader “JerseyShooter” has been working with Sigma to improve the performance with Canon's APS-H flagship cameras, the EOS-1D Mark III & EOS-1D Mark IV.
Back in October of 2013, JerseyShooter started a blog documenting the issues he was having with the lens on a blog. He worked directly with Sigma and it looks like it has paid off with the firmware that was released yesterday to improve the performance with both of the mentioned cameras.
There have been other issues with the lens that he is documenting on the blog as well.
For the record, JerseyShooter is an employed professional photographer.
Read the blog about the Sigma 120-300 f/2.8 OS Sport
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