This is one of the lenses I tried out for street photography, specifically to find a lens with the ability to form a sharp image across the frame, combined with a generous amount of field curvature. That way features closer to the edges and the main subject in the centre can both be in focus; more on that in a previous post.
This lens seems to have a wavy characteristic when it comes to field curvature: a mid-zone between edges and centre is less sharp than the edges and centre themselves. This is not unusual, I see this a lot with Minolta wide-angle lenses, it is however difficult to work with in practice. The effect becomes more pronounced on stopping down, it is especially visible at f/5.6 and f/8. For landscape use I’d stop down to f/11 where most everything in the frame is in focus. That said, I prefer the Olympus OM Zuiko 28mm 1:3.5 for landscape use and the Pentax-M 28mm 1:3.5 for street photography.
There is some distortion visible when straight lines are in the frame. I don’t care about it because I always make a custom profile for Lightroom to correct for it.
Some contrast loss and flare in the centre at f/2.8 as expected, very sharp at f/8.
Fairly normal results. Note the purple fringing visible at f/8, this can be fixed in Lightroom and is also common for legacy wide-angle lenses.
Here you can see that it’s not very sharp when moving from the corner towards the centre, due to the curvature of field I mentioned before.
If you’re so inclined, you can examine the test files for yourself in the gallery with full-resolution pictures.