[davidmanze]

Sorry, I'm very late.

 

The diamond shaped reproduction is likely a result of pinched optics, basically a lens being held in place too tight and causing a physical change in the element. 

 

Could you please expand on this thesis?  

   

      I guess it's Sigma's new superheated steam system of AF causing stress in the lens barrel  with the different co-efficients of expansion between different materials, Sigma were obviously aware of the problem and  took many measures to alleviate it, hence the low dilatation plastics.

   As far as I'm aware they used technology from the famous Doble steam car of the late 1920s which was noted for it's rapidly heating boiler system with record-breaking  point to point speeds coupled with an  extraordinarily silent drive engine.

    In modern day times it's so easy to lose sight of our technological roots and shun some of man's greatest achievements,  it's good to see that Sigma is still paying tremendous respects to our forebears here, so it seems somewhat churlish to be "carping" about very minor shortcomings  which can stem from holding up such high traditional principles.  After all diamonds are forever!