Originally posted by LightBug
There should be a menu item that locks exposure when focus is locked.
With the K-70, like other models where the AE-L button has variously assigned functions, it may not be set up for its labelled function, so it did not lock in your spot-metered exposure. That is what I see in your first photo.
Your other photos using matrix metering look as expected in terms of balance between light and dark areas, but they do seem a bit underexposed to me, especially the ballpark scene. Almost to the degree similar to my old K200D.
The only way to tell if this is a lens issue is to take the same scene, same framing, with no change in lighting with the DA 21mm and another lens set to the same aperture and shutter speed.
I've had this lens for some years, used first with my K-5 which does also tend to underexpose very slightly, but more accurate than the K200D, and have gotten great images with it, even without careful metering under normal conditions.
Actually, in looking again at your first picture- I wasn't there to see the lighting conditions in reality, but my guess is by spot metering off her face, which was very much in shadow, if it went the way it should, it would greatly overexpose the rest of the scene. Her face is a comparative extreme in the overall lighting. All you want to do is open up her facial shadows to a degree, so her face is more visible. If using spot metering, it would be best to meter off a mid-tone in the scene, like off of a lighter area of the building on the right, or even off of the better-lit gray pavement of the street below, lock exposure, or use the green button to do your spot metering in "M" mode and see how that turns out. The other way is to simply use a pop of fill flash with the camera in "M" mode and metering for the entire scene first, using the green button then popping up the flash, since the flash would not affect the more distant part of the scene. You can also modify flash output by using the flash comp control, according to the effect desired, and the ambient lighting of the scene compared to your subject.
I find it desirable as a general rule to use flash when subjects are close even in an evenly well-lit outdoor scene anyway, as this will put a catchlight in the eyes, and more evenly reduce harsh facial shadows from downward or sideways lighting. Especially also when subjects are wearing hats or caps, which can easily darken the face.