08-29-2013 05:42 PM - edited 08-29-2013 05:43 PM
11-14-2013 02:25 PM - edited 11-14-2013 02:27 PM
My guess is that it uses those rings to calculate both chromatic aberrations and vingette. Since its not a Canon brand lens it gets stuck in the process.
If you disable just one you'll get one ring...
03-08-2018 01:30 AM
03-08-2018 09:30 AM - edited 03-08-2018 09:38 AM
I accept that Sigma, Tamron, and others make some decent glass and in some cases have a feature set unavailable from Canon but these are the sorts of issues that can happen when a compnay has to reverse engineer compatability with a camera body. It sounds like the causes/work-around has been identified in this thread which again shows how valuable forums like this are for owners.
I am intrigued by Sigma's upcoming 105mm F1.4 lens (a combination not available in Canon glass) but it is threads like this one that give me pause that little quirks may be present. I will probably end up with a Canon 85mm 1.4 instead.
The best "glass" you can justify/afford is the best investment in your future photography. A good lens will outlast several generations of bodies and will provide the best your camera body can deliver. When I was finishing up the PhD program when the EOS line first came out I "saved" money by buying a couple of aftermarket lenses-a mistake I won't repeat.