Some months ago, while I was in an observatory in Arizona, I bought an unit of the Samyang 135mm F2 for my Canon 6D (Full Frame) and I got a lemon. Amazon offered to exchange it, and I got another lemon. Not believing my bad luck, this last week I bought another unit in Amazon Germany, thinking that maybe I was just unlucky and got two units of a bad batch ... well, does not look like it, I got a third lemon and enough to say that Samyang QC is just plain horrible. Even more, by default it does not focus to infinity, but maybe to 50-100m max (it can be adjusted, but you have to disassembly it, not really that nice).
It is also interesting to note that it is not sensor tilt, as in different units the corner that looks the worst changes.
I cannot but strongly suggest you to stay away from the Samyang/Rokinon lenses, in particular this well reviewed 135mm F2.
Edited by elakrab, 17 March 2020 - 11:05 AM.