[JJ_SO]

 I think you've made a good call with the Quatro, I like 21mm FL...................................................................................................

 

 

 I notice the Sigma publicity shots major heavily on very dark shadows, I hope these can be recovered in PP, it's a little too dark, Arty though!

Matter of taste, I think.

 

In PP (and if the user is patient enough  ) are shadows very easy to recover. Bigger problem are highlights, so if in doubt, I make a darker picture as well. The X3F fill light is a quite powerfull tool to get back the shadows.

 

There's also a checkbox to tick "lens profile" and Sigma is delivering new lens profiles from time to time. Remember, the PP app is not only for fixed lens cameras but also for SD1 Merill with interchangeable lenses. This lens profile includes correction of CA. As described, the main target at the development of the lens was less than 0.5% distortion. They succeeded at the cost of speed. The lens designer wanted f/3.5 but that would have made the distortion goal very expensive.

 

I'm very happy they took care about distortion - it can be corrected in post, but not in PP and would lead to transforming calculations on pixel level at the cost of resolution or picture size.