I'm in for a macro lens purchase and would have picked the Canon EF 180mm/f3,5 L USM Macro if I wouldn't have stumbled over the Sigma 180 mm F2,8 EX APO Macro OS HSM.

Can anyone give me some first hand experience with either one of these or maybe someone had a chance to shoot with both? I'd greatly appreciate it.

What's the practical advantage of the f2.8 of the Sigma over the Canon? DOF when shooting macro is paper thin anyways, so I assume the f2.8 might be a nice feature for portraits?

Eventually, I'd love to combine the macro with a teleconverter - is someone here utilizing that as well?

Looking forward to hear some opinions.

I have the Canon 180mm macro lens and like it quite well.  I've used it for both macro images as well as a fixed lens for "normal' shooting.  Bokeh and overall quality are fine.  I rarely, if ever, use the auto focus feature as the majority of my macro shots must be stacked due to shallow DOF so I must manually focus either with the focus ring or using a rack & pinion micro adjustment tool.  I've never used the Sigma lens so cannot offer any direct hands-on comparison.

Both of those lenses take an expert to use and the output is not very stockworthy.

Use it for portraits? ja, you can also use wide anges for portraits..

Said the man who has never tried any of them.
But what I have.. .Is that I have extensive experience with macro lenses up til the sigma 150.

I would say you should only buy any of them if you have a special interest in small insects and want to capture their antenna or front legs, because the species is important to you.
With macro lenses there are two important features: is it sharp, and yes they all are and does it have a good bokeh. And no they dont have that. Especially the nikons are bad. Nikon 105 has a very bad bokeh that leaves everything blurred appear in double lines. The cannon 100 is better, but has an insignificant bokeh.
Sigma 150 macro, has a splendid, different and unique bokeh.

And this is why I wrote this post, despite i dont know either of the lenses. I just wanted you to compare the bokeh in the 2 lenses, if the sigma 180 holds what the sigma 150 promises, it will far outbeat the canon.

BTW bokeh means " the quality of the unsharp areas", look for fringing, double lines, burnouts or even artefacts.

making small things big

I better not touch that one or my wife might kill me 

I don't agree a lot for a 180 mm for macro. With a so long focale the minimal movement will result in a blur (even using a tripod), unless you take all you photos with fast strobes.

I think that a 105 mm is a better compromise for most of the macro and portrait photos (with a 180 you will have the ears ans the nose on the same plan ), and surely the sigma 105 is the best quality/price you can find.
http://www.techradar.com/news/photography-video-capture/cameras/best-macro-lens-for-nikons-8-tested-1079616/9#articleContent

Just my opinion of course.

Thank you! Good point!!!