Back in May I started a thread about Effective aperture, a concept I was unaware of until I experienced it on my Sigma 150mm f2.8 OS macro lens. I was experiencing a 2 stop underexposure with this lens when used for close up/macro with a Canon 7D2. This was irritating because the amount of underexposure and therefore compensation varied with distance and the lighting conditions.
I thought it worth reporting that, following discussions with Sigma, I discovered they had a firmware upgrade they claimed would resolve the problem so I recently sent it off. Today it was returned to me ( within a week!) and although conditions here are not particularly conducive for photography it seems that this rechipping has indeed resolved the problem as far as I can tell from a few test shots.
Sigma produce some great lenses but sometimes get criticised for poor service, I have to say I cannot fault them particularly if the improvement I have so far seen in the lens holds up to further testing