Tareq wrote in post #18434773
How do you compare another 135mm i mean another brands to this Canon 135L?
In astronomy forums i see many favor Samyang 135mm, so doe it perform better than Canon 135mm for example?
Also Sigma 135mm Art, is it really better than Canon one as Charlie mentioned? i didn't use 135mm for anything really but only some test shots in the past, now i may think to use it for astro, but is it still good for that or better replace it with another newer 135mm lens? i don't think i will think about mkII from Canon, as usual, more price like doubles and the quality isn't much as double maybe even with IS, and i won't die for higher quality from Canon for much more price.
have you ever replaced a 24-70 mk1 for 24-70 mk2
70-200 f2.8 IS vs 70-200 f2.8 IS ii
17-40 to 16-35 f4
you'll notice it right away, on a higher MP body, the sigma absolutely bites down hard.
the 135L compared to the 85 f1.8, seems like it's got cleaner colors, better contrast, while the 85 seems a bit hazy in comparison. When compared to the art, the 135L becomes the hazy one, less contrast..... I have no doubt in my mind that the 135 art is at least comparable to my brother's 200 f2 L, probably cleaner. It feels like you have to stop down to F4 of the 135L to match the 135 art, it's crazy sharp wide open @ 1.8, and it gives a touch more blur.
I was in ignorant bliss with the 135L for the longest time, but when I switched from the canon 100 to sony 85, there was a bit more clarity and sharpness to the 85 shots that it made my 135L shots a bit lackluster (shooting portraits in hazy conditions).... so on a whim, I decided to swap to the art. Back to bliss 
While it's much heavier, size is about the same and since the sigma is more flare resistant, I dont use the hood with it, so it's no larger in practice. Neither 135L/135art will ever be a travel lens for me, both are too big, 300+ gram 85mm is about as big as I will get for travel.
Sony A7siii/A7iv/ZV-1 - FE 24/1.4 - SY 24/2.8 - FE 35/2.8 - FE 50/1.8 - FE 85/1.8 - F 600/5.6 - CZ 100-300 - Tamron 17-28/2.8 - 28-75/2.8 - 28-200 RXD
Panasonic GH6 - Laowa 7.5/2 - PL 15/1.7 - P 42.5/1.8 - OM 75/1.8 - PL 10-25/1.7 - P 12-32 - P 14-140