Not surprising, but the Voigtländer 21mm is wide and therefore a little tricky for me. However, it's a good challenge to view things with this new expansive eye. 

The Voigtlander Color-Skopar 21/3.5 ASPH II isn’t quite the performer that reviews have led me to believe. Not all that surprising since most reviews were with lower resolution cameras. The M11 is no easy challenge for lenses and I think the 21mm lens falls a little short here. It’s just a little disappointing, but let me elaborate since it’s not a deal breaker...

With lenses there is a typical triad of compromises; compactness, performance and price… Pick two! Most often than not, this is the rule and not the exception. You can obviously guess which catagory the 21mm falls into. Compactness, depending on the photographer, is sometimes worth a lot in the form of balancing compromise. 

The Color-Skopar 21/3.5 ASPH II is brutally sharp in the centre third of the frame. Just shy of the mid-frame mark sharpness tapers off fairly strongly to the edges and corners. While detail isn't soft at the mid frame, edges or corners, it’s not rendered with the biting resolution of the centre, which makes the difference so stark. This difference will be far less apparant on a 24MP camera, which is why this lens never got reviewed as a soft lens. 

It's not the sharpness throughout the frame thats the biggest culprit to a pottentially dissapointing impression of this lens… that honour goes to field curvature, and unfortunately it’s quite strong. At infinity focus, the mid zone and edges won’t be sharp at f/8. With a very strong moustache shaped curvature, the focus plane makes a strong bend towards the foreground and then the edges move a little outward again but not as far as the centre. Keeping this in mind will help in achieving better cross-frame performance, however, at f/8 and even focusing past infinity (with lens adjustment) perfect cross frame sharpness isn’t possible.  

I think the easiest is not to fight this trait and to work with it. Otherwise, your best alternative is the heavy and large Voigtlander Nokton 21/1.4 lens or the four to five times more expensive Leica Super-Elmar-M 21/3.4 ASPH. For $650 to $799 depending on version of the Voigtlander 21/3.5 ASPH, this is a good compromise of price, size and quality. And no, TTArtisan isn’t an option for me.

When shooting a landscape, I back-focus the centre as far as possible. The central third area has a very large depth of field that just increases exponentially when stopping down. You can pretty much rely on that to sort itself out, so prioritising focus for the edges is probably the best choice. The image below was photographed at f/8 and focused to the lens hard infinity stop. I marked the image to show where the centre and edges are focused. I also provided crops from the infinity center focus point, the infinity edge, and where the edge is optimally focused due to the field curvature. 

Field curvature like this isn’t uncommon with wide and ultra wide lenses. However, reducing this will demand a more complex lens design which will increase the complexity of the lens, inevitably resulting in a larger more expensive lens.

It also depends on the photographer and the type of subject one photographs. For my purposes, while its annoying, I’ll be able to live with it and work around it as best I can.