The Photozone rating
Quote: The Pentax SMC-DA 21mm f/3.2 AL Limited is a very good lens but it is not as special as its longer cousins (specifically the Pentax FA 31mm f/1.8 Limited) nor is this really possible because of the increasing design problems when pushing things towards wide and ultra-wide angles. The center performance is exceptionally high whereas the borders require f/5.6 to achieve very good levels. The amount of barrel distortions and vignetting are Ok but nothing to rave about for a new fix-focal lens. CAs are quite well controlled. The coolest aspects of the lens are naturally the extremely small size, the very low weight and a relatively moderate price tag of around 500€/US$. Combined with the "longer" pancakes lenses, the DA 40mm f/2.8 Limited and DA 70mm f/2.4 Limited, you'd have a complete yet very unobtrusive fix-focal lens setup for street photography.
And rated at 3 out of 5. I look at that and I think, this is someone who hasn't used this lens. I bought the lens largely on the advice of forum members, couple with the fact that I found one second hand at a very reasonable price a 2 hour drive away from me.
You look at the specs for this lens and they are nothing spectacular. Until you see this...
Or this
There is a dreamy quality about these images that no other lens I own achieves, although I've seen evidence that the 31 ltd is similar. You don't want that quality in every shot you take, but when conditions are appropriate, there is no other lens I own that is going to give me that. Photozone says "good for street photography" to which I respond "huh?". So what I'm saying here, is in my experience, what the people say about a lens that use a lens is more informative than what you read at the test sites. In most cases, they haven't used the lens enough to know what it's even good at. Photozone doesn't have a clue about what the best quality of this lens is, and they don't have a test for it. It's nice to have the numbers when arguing sharpness etc. but based on the Photozone ratings, I wouldn't have bought this lens. And I'm really happy I didn't look up the numbers until after I bought it. I would have missed out on an awesome lens, and some awesome pictures. Maybe not for everyone... but, I'm not everyone and neither is anyone else. Photozone simply cannot define in numbers what it is this lens has.