Here's what £24 worth of CCTV lens gets you...
Lumix GX7 with Picor 25mm f1.7 CCTV lens - 1/60 - ISO 1600 - around f4 to 5.6.
...the center is pretty sharp, but unsurprisingly the edges are very, very soft, with a lot of vignetting (even wide open it's clearly visible). so you have to frame accordingly and then crop in post if you want your subject off-center (as above).
This shot I planned to be B&W from the offset and wanted a film look to it, so while it's had work in lightroom, none of that includes any noise reduction or sharpening from the RAW file. I'm vague on the aperture setting, as the ring doesn't have any stops on it, but is a smooth twist from open (f.17) to closed (f8), however, it does seem to stop down more than f8, as it goes past the marking for that.
Its use, given the above, is limited, but it's also only £24 (lens and adaptor for M43), so will certainly get more use.