Primes Sigma vs. Canon

I'm going to buy a 50mm and an 85mm and my question is pretty simple:
is the Sigma worth the extra money in both FL? and how is the focus compare between the two lenses (50vs50 and 85vs85)
My use for the lens would be portraits (85mm) and a walk around low light (50mm)
money is an issue but I'm able to afford both sigma's
P.S I'm talking about the canon F1.4 and F1.8

thanks for your thoughts

Personally I'd go sigma for both of those if I had the money (for the 85 especially, which is quite pricey).

The focus on the 85 will be slower (the canon 85 is pretty darned fast in terms of AF), but the 50's should be about the same as the canon has a micro USM motor while the sigma has proper HSM, which offsets the usual speed advantage canon has in the AF department.

You say money is an issue however. I think you'd be very happy with the canon 85 1.8 and the sigma 50 1.4. The only faults with the canon 85 are the colour fringing and less than desirable MFD, otherwise it is sharp, small, and has fast AF, so its hard to not recommend it.

i would say stick with the Canon 85 1.8 and just concentrate on getting a good copy of the Sigma 50 1.4, only get the Sigma 85 1.4 when you feel like the Canon 85 is holding you back.
the Canon 85 1.8 is probably one of the best bang for buck

Best thing about Sigma 85mm f/1.8 is less CA compares to Canon f/1.8. CA is quite easy to fix in the post. That 0.5 stop does not gain you that much otherwise.

Sigma 50 however is quite a bit better than Canon 50 1.4. Just make sure you are willing to send it for calibration if needed. I had two copies and both required a bit of MFA, but it was within +/- 20 so just used 5d2's MFA.

the Sigma 50mm 1.4 is an amazing lens. Its almost Canon 50L quality minus the price tag. If you can get a good copy or just send it to sigma for calibration you won't be disappointed. I'm thinking of picking another one up.

I really like the Canon 85f1.8. It is a sharp lens with super fast AF. I'd recommend it highly.
I have the Canon 50f1.4 and mine is very sharp. Personally, I think that you are going to be better off with Canon lenses in these focal lengths. Yes, I know about the AF problems that some have had with the 50. I have also read that it helps avoid these problems if you keep the hood on the lens at all times, and I do that.
I have also read that the Sigma has focus shift, which can limit use in some situations.
I have the Canon 50f1.4 and the Sigma 50f2.8 macro lens, and couldn't tell photos apart at f2.8.
The Canon is a good lens, and has accurate AF. AF on the Sigma macro lens is accurate, but slower than the Canon. I can't speak to personal experience with the 50f1.4 Sigma, but I went with Canon and I am glad that I did.

thanks everybody for your input!
I think I'll keep the canon 85 and go for the sigma 50 (keeping my finger crossed that I get a good copy with no need for a MFA)
Although it's hard to pass on that creamy bokeh of the sigma...

The build quality of the Canon 50mm 1.4 is really bad. It's not as bad as the 50mm 1.8, but urggh. I enjoy my Sigma 50mm 1.4 very much and would recommend it. As the others said, have it calibrated if the AF doesn't work properly...

Out of the 2, the sigma 85 is the safer bet as it's less prone to issue. It's a class above the Canon 85 1.8.

Sigma 50 is again a class above Canon 50 1.4 but be ready to send in for cablibration.

Both are close to the Canon L equivalent at less than half price.

Used to own both and now left with the Siggy 50.

I lost the sigma lottery. At first, I thought I hit the jackpot. Incredible result at 1.4 with amazing bokeh and color. When I tried taking picture at the subject that are more than 1.5m away, the picture was horribly out of focus. Returned the lens to the service centre and it came back the same. Did some talking to the store and turned out the whole batch of ther lens suffered the same problem. In the end, I decided to refund the lens instead of sending the lens to Japan for calibration.

Wow that's unlucky! Here in Sydney we have a local Sigma service. They do send to to Melbourne where they have real calibration technicians/equipment/​whatever, but back and forward it only takes a week. When I brought my 30mm 1.4, they returned it to me perfect, it's tack sharp and very fast. Before calibration, wide open it front focused about two inches, which when you use it at close distance was enough to have the eyes completely out of focus.

I quote here from the Photozene website:
"The HSM ("Hyper-Sonic-Motor") AF is very fast and virtually silent. AF accuracy is a difficult topic for the Sigma. It seems to suffer from pronounced focus shifts when stopping down ("Residual spherical aberrations") which is probably the reason why many users report back- or front-focusing issues."
There are other reports of this as well.
This is why I went for the Canon 50f1.4 (for low light), and the excellent Sigma 50f2.8 macro lens. The Canon is very sharp stopped down, and AF is accurate. I admit I am worried about the life of the AF on the Canon, but this is not my most used lens.

I looked closely at replacing my Canon 50/1.4 with the Sigma... decided the difference in IQ wasn't worth the money or the large size and weight of the Sigma (who ever heard of a 50mm lens that needs a 77mm filter!). The Sigma is slightly sharper wide open, but gets softer than the Canon from f5.6 and smaller. The Sigma has more aperture blades (9 vs 8) which makes for slightly smoother background bokeh in some situatioins. But, the difference really isn't huge.

The biggest problem with Sigma is they seem to show up uncalibrated. Maybe they are doing better now, but search here on POTN and you'll find lots and lots of posts about the problems they seem to have with AF accuracy. Keep in mind, with larger aperture lenses AF accuracy is more critical.

A lot of Sigma 50mm and 85mm (and 30/1.4) buyers either have to keep swapping until they get a "good copy" or dial in a lot of focus Micro Adjust (if their camera has that feature) or send the lens in to Sigma for calibration.

I've got and use the Canon 50/1.4 and 85/1.8. They are excellent lenses. Not perfect, but no lens is.

If you get the Canon lenses be sure to get the lens hoods, which aren't included (hoods are included with the Sigmas).

The Canon 50/1.4 is considered a USM lens, but actually uses sort of a hybrid form of AF drive, based upon a micro motor. It's plenty fast and accurate, but a little fragile. The lens hood protects it pretty well, both in use and when reversed on the lens for storage. That might be why my 10 year + old 50/1.4 is still working great.

Oh and both the Canon lenses use 58mm filters (as do a number of other Canon lenses).

So I just got some unexpected money, so I pulled the triger on the 50 and 85 both sigma!
let's hope I get a good copy that I don't need to send back!
Thank all of you for your advice it's been very helpful

Congratulations! I guess you made an excellent decision.

Please let me know about your Sigma 85. I am too debating on Canon 85 vs Sigma 85. I already have Sigma 50mm and love it, no need to send it back for calibration etc.

Thanks, Pendu