My Laowa 15mm a bad copy?
There is still a hope - it looks like that my copy of Laowa 15mm f4 lens is a bad copy. Here I compare the extreme bottom left corner of a shot made with a better copy of Laowa 15mm (center photo; taken from www.flickr.com/photos/dierktopp/21310940211/) to the same made with my copy (right shot). The left shot was originally made with a full frame camera, but the pixel density is very close to the density for my crop camera (Canon 50D), so I simply cropped the full frame shot to match the pixel size of my camera sensor; no rescaling was required (which is good, as rescaling always makes photos more blurred). I also show the same area done with my Sigma 10-20mm lens at 15mm (left side). All shots were made at f/11.
The right shot (my lens) looks significant softer than the center one. In fact, the good Laowa copy (center) seems to be also sharper than my Sigma 10-20mm (left), which is a good performer. I think I have a good case for trying to exchange my Laowa lens for a better copy.