Read this before on different forums that the Sigma 85mm f/1.4 underexposes 1/3 to 2/3 stop compared to Canon 85L, even at manual mode.
A couple of weeks ago, there was a photographic show here. I brought my Canon 85 f/1.8 and did some comparison shot with the Siggy 85. Shoot at manual mode, with same ISO, different shutter speed and aperture combination. Also shot a few video clips to compare.
The siggy under the same ISO, f/1.4 , 1/160 sec shutter, the exposure is almost exactly the same as f/1.8, 1/100 sec shutter with Canon 85. Also tried f/1.4 and 1/200 sec shutter, it's slightly ( a little) darker than f/1.8, 1/100 sec with Canon 85. The video clips confirm the same thing.
I'm sure that the Sigma 85 is indeed 2/3 stop faster than the Canon 85 f/1.8. At least in manual mode, which is what matters to me most.
Hopefully this is helpful to people who are thinking about upgrading to siggy 85, but concerned about the real speed of the sigma.
I will post pictures later after I upload them.