Hello! I started photographing in 1962 (nineteen sixty-two) while in the 7th grade. I was 13 years old and used a Rolliecord TLR and a Weston light meter. So, yup, I'm old (63). What I didn't realize was that that moment in time was the beginning of a life-long love of photography which resulted in my using a myriad of equipment and taking thousands of film photos.
I know what this lens is capable of producing via internet postings on this site. I read of its foibles was positive that given my skill set that those issues could be handled. What I truly discovered was that it's a fully compromised piece of glass from a mechanical sense. Having had many Nikon and Zeiss lenses, as well as some medium grade 3rd party glass, I'm familiar with how to use each type. No problem.....
What was surprising was that it did NOT work properly after being mounted on my camera: it grossly underexposed every shot that I took, regardless of where the photo was taken as well as the lighting condition (really dark settings excluded). I checked ALL of my settings on my camera; all were nominal. This lens is in Canon's listing of recognized lenses (of course) and that registration was shown in the camera's menu. So, I remounted a Canon 50mm f/1.8 (original version-still registered...) and all was perfect. Hmmmmm.... I checked the manufacturing date and it was August 2012--so, all okay from that standpoint.
Although the above problem could have been from user error, I'm inclined to think not, as I've been using many types of digital cameras since 2007 and have never had this problem.
Given the L series of lenses and the quality control that is required, I'm sure that it passed all of their tests. So, the reason for it not producing a properly exposed image with my Mark III is perplexing.
In conclusion, I'm exchanging it for Canon's 35mm f/1.4 USM. It is a very different type of lens perspective, but from what I have read here it's a gem.
I wish that this lens was a keeper, as I think that 85mm is a great focal length for many types of shooting. I'll have to check-out Canon's other 85mm listing(s).