Interesting that you haven't gotten any responses to your post. This is possibly because you really have answerred your own question. It really gets down to which focal length is best for you. Despite all the "press" the 85 gets, optically the two are very close. in fact the 100 is perhaps slightly better:
www.photozone.de/canon-eos/166-canon-ef-100mm-f2-usm-lab-... However, only a pixel peeper is going to get aroused by the difference. they are both great optically. Speedwise, obviously, the 85 has the slightest advantage, but only 1/3 stop, to me almost insignificant. So it gets down to best focal length. Only you can decide that. In your case it may get down to are you going to be doing more indoor sports or portrait work? I use my 100 F/2 for indoor sports when I can't use flash. It is my "go to" lens for this. I use it on both cropped sensor and full frame but more the latter. For my use I'm sure either the 85 or 100 would work but the 100 is probably a little better length. I'm sure this doesn't help you much.
ages ago(permalink) offbeat payment [deleted] says: Just personally I find that I like longer portrait lenses. So I like the length of the 100mm on my 450d. But thats me.
ages ago(permalink) 
wiredfool says: It's a tossup. The 100 is just a little long for me inside for portraits and such on the 1.6 crop factor body. It's nice for tight headshots, but more than that and you need serious room, which for me would require an upgrade to a bigger house. They're both excellent lenses. You're not going to go far wrong with either. (or both.)
Originally posted ages ago. (permalink)
wiredfool (a group admin) edited this topic ages ago. 
Four Winds Photo says:"You're not going to go far wrong with either. " Best point yet.
ages ago(permalink) 
xc1943 says: hey thanks for your opinions. im still not decided, but your opinions did help. thanks a lot
ages ago(permalink) 
The Magic Hour (Chris) says: As others have noted, the choice of lens boils down to what focal length best meets your needs. I've used both the 85mm and 100mm, and found both to be excellent. Ultimately, I went with the 100mm for my full-frame camera, and am very happy with my choice.
ages ago(permalink) 
neoplatonistking says: Rent both and try them out! I'm renting the 100mm f2 right now and I have really fallen in love with it. I especially like it for portraits even on my crop sensor camera (XSi/450D). It is razor sharp even at f2 and focuses lightning fast. The bokeh is excellent. I don't think you can go wrong either way. This was taken in low light wide open with the 100mm:
Originally posted ages ago. (permalink)
neoplatonistking edited this topic ages ago. 
northernlightphotograph says: As someone else said, I also prefer the tradeoff of a longer portrait lens that the 100/f2 offers. Mine is tack sharp @ 2.2 and still very sharp wide open in low light. The payoff for me when using this lens on a Rebel is the size. For basically the same size as the 85mm, the extra reach this lens has is worth it in anything other than portraiture. And this lens does so many things so well. People unfamiliar with it are floored when I tell them it's a 100mm lens.
Originally posted ages ago. (permalink)
northernlightphotograph edited this topic ages ago. 
TauroDont says: hi , i am a newbie ..
i am planning on a portrait lens that works well in low light . choice is down to these 3 .. canon 50 mm f1.4 ( is this outdated ??)
canon 85 mm f1.8
canon 100mm f2.0 .. i use a canon 500D.. please advise
ages ago(permalink) 
wiredfool says: Well, what do you do now, and how does it work? What do you need to change? What's your framing like? Are the portraits head and shoulders, or full length? Indoors or out? Do you have a ton of room? Do you want the compression from a 100, or less compression from a 50? (or normal from a 35, for one other option). Absent that I can give you one of three answers: - It depends.
- They're all good lenses.
- The 100 is 2x better than the 50, and 15% better than the 85. or vice versa. Or at least, longer.
ages ago(permalink)
TauroDont says: thnx for the reply
i will be taking indoor and outdoor portraits ..
wt would be the minimum focussing distance on the 100 mm ..
i have narrowed down my choice to 85 mm or 100 mm
is there a website that gives the specs for these above lenses ?
ages ago(permalink) 
wiredfool says: Those lenses are pretty similar. The minimum focusing distance is about 1 meter or so. I find the 100 is a bit long on a crop body indoors for anything but headshots.
ages ago(permalink) 
VirtualWolf says: How's the chromatic aberration compare between the two? I've seen some mentions of noticeable CA on the 85mm when shooting wide open, but haven't seen anything about it on the 100mm (again, wide-open).
ages ago(permalink) 
Lee Welton says: Yes same CA probs wide open.
ages ago(permalink) 
northernlightphotograph says: I hate to say this because I was dubious myself. But if you can find a good used 50mm f1.8 MK I I'd get it over the 50mm F1.4 USM. I used to justify owning the 1.4 but recently found what seems to be a very sharp 1.8 MK I. I sold the f1.4 within the week. You will lose the USM, but the AF speed on the 1.8 MK I is actually pretty fast. Noisy? Clear your throat or sigh as you shoot if that's such a concern. If you can find a nice 50mm f1.8 MK I for $150 or so, it might free up some resources to get the 100mm f2. Which was my logic.
ages ago(permalink) 
Monkey Mash Button says: I've borrowed the neighbor's 100mm f/2 to use on my T2i. It's an amazing lens no doubt, but you have to be pretty far back for portrait work. For a full length shot of an adult, you'd have to be 25 or 30 feet away I'm guessing. | 
