Sweet! Mom always told me I was wise! 
kfyount wrote in post #13088647
I don't disagree with cptrios' wise words. I think that is most of the reason that the 100 f/2 is less popular than the 85mm f/1.8. But, I've also read about the CA point that JayStar86 mentioned - it seems that the 85 is not so bad or it would be more of an issue to sway people to the 100.
However, when I was deciding, I went with the 100 because it fit better with the 50mm that I already had. Nothing to say that one can't have a 50, 85, 100, and 135, etc. - but I thought that 50 and 85 would be too close together to be useful. Also, I find the 160mm effective FL comes in handy in more cases than it might seem.
Don't get me wrong, I think it's a perfectly good lens on a crop camera, but its lack of popularity on that format is as much a matter of perception as it is of actual utility/quality. 160mm just isn't a generally established focal length for any traditional purpose, and therefore is never going to be popular. I loved it when I had one on my 40D, but at the time I didn't have a huge budget and the FL simply wasn't useful enough to me to keep it around. Well I don't exactly have a huge budget now either, but 100mm is very nice on FF!
JayStar86 wrote in post #13088670For FF users I would have thought it to be the more popular lens, especially, to pair with the ever popular 50mm 1.4.
I would have thought so too, especially given its better purple-fringing suppression over the 85/1.8...but perhaps there's a big psychological difference between f/1.8 and f/2?
Thats what Im going to end up doing very soon once I sell one of my current lenses. I will have the three lenses on FF : 28mm 1.8, 50mm 1.4, 100mm 2.0... cover 90% of my shooting needs and someday*** get the 70-200 Mk II
28, 50, and 100 are the FLs I have at the moment too. Pretty nice combination, in my opinion (though I'm swapping the 28 for a 24 soon). 100mm is my favorite FL out of 85, 100, and 135...it's kind of a "goldilocks" medium telephoto FoV in my book. 135 is a bit too long as a walkaround, and 85 is often just a bit too short. However, if I had a 35L instead of a 50/1.4? I dunno, I think I might go with the 85 instead. But if I were to get a 35L while still having my 100/2, I'd leave it at that.
You know what I really would like, though? A fast 70mm prime. I love my 25-70 zoom, as the 35 and 70 just feel like great FLs to me...but I wish it were a constant f/1.4!
