HD Pentax-DA 21mm F3.2 Limited
Vignetting
The DA 21mm shows a small amount of vignetting (darkening in the corners) at F3.2, which is all but gone by F5.6. The table below shows a studio shot of a white board taken at one-stop intervals, showing the mild darkening wide open and a mostly uniform brightness when stopped down.
At F3.2, the light falloff is approximately 15% in the corners. In most real-world situations, this is just starting to be detectable. By F5.6 the falloff is less than 3% and would not be apparent.
This is a respectable result compared to other wide lenses.
Click on any image below to see a larger size and scroll through the other apertures.
Vignetting for the DA 21mm Limited. (Click for larger images.)