[toni-a]

Today I saw Sigma 50-100 ART, I am hesitating to get it.

it is not stabilized, this is the major drawback.

Since I am on dual system full frame and APS-C, I am wondering what is the better choice, getting a 70-200f2.8 OS or the 50-100f1.8, it is not about low light capacity but about sharpness, bokeh and what you ask from a portrait lens.

which one do you expect to be the better choice ?

 

[Klaus]

I'd say that a f/2.8 lens is usually always better than a f/1.8 lens.

Whether the current (rather old) 70-200 OS is the better choice my be a different question.

I'd rather wait for the Art version (or go Canon). 

[Rover]

Lenstip has reviewed the 50-100 and the sharpness is off the scale. Dustin Abbott has also evaluated it and shown how easily the vignetting can be cleared away in PP if you're using this lens on Full-Frame (at least towards the long end). I think the 50-100 would've made an excellent part of a 3-lens set with a 16-35 and 100-400 lenses, but the lack of stabilization (and weather sealing) is a little discouraging.

 

I would also look at the Tamron 85/1.8 in addition to the 70-200, but that's just me.

[JJ_SO]

I'd say that a f/2.8 lens is usually always better than a f/1.8 lens.

 

I doubt this statement, especially because you can't decide between "always" and "usually". Either one or the other 

 

I also doubt that in terms of bokeh there are a lot of 70-200 lenses beating this Sigma speciality. But I think one needs to decide: For portraits FF and a zoom - hands off the Sigma 50-100. For APS-C a very nice portrait zoom: very different story, although same weight, same price. I'd at least give it a try before I'd say no to it. And I would use FF for portraits.

[toni-a]

now i am totally confused.

Full frame is great for portraits undoubtedly, but my 759D is much more practical for hiking traveling and even general landscape and nature photography since it has more Depth of field, for macro shot I can have more distance to the subject, besides it has very practical tilting screen and live view.

Was trying to stay with one system seems I will be keeping both, neither lens is practical for hiking nor  traveling. 750D for traveling and hiking and general use, full frame for photoshoots

[JJ_SO]

... it is not about low light capacity but about sharpness, bokeh and what you ask from a portrait lens....

That point's toward the Sigma, if you want such a lens for 750 D.

 

Actually I have no idea how a 1.5 kg lens would fit in the "hiking" bag - but that goes as well for the 70-200/2.8!

And the basic problem with your hiking bag is simply "weight and size of body and lenses are bigger than any comparable mirrorless system"

 

What's to say against the 70-200/4?