I used this lens for my "Single in September 2020" challenge having just bought it from a UK Pentax User Group member. I have a bit of an addiction to K series prime lenses, and have 25 of the possible 34 models. I was using a Pentax K-3, and so the image circle is cropped a little making the lens feel like a slightly wide normal rather than a not-very-wide wide angle lens. (For many years I only had 28, 50 and 135 lenses and so I'm used to 28mm for my wide angle.) I quickly got to like it, however, and when focused well it is very sharp for a 45 year old lens (and probably an older design). I did find, however, that to get really good critical focus I was using live view and zooming in. The green hexagon focus confirmation on my K-3 was OK, but not as good as using the live view. This maybe my K-3 which has seen six years of continuous use including many aircraft journeys and, recently, bicycle rides on very bumpy roads. As with all my previous dSLRs (K10D, K20D and now the K-3) the "green button" method of setting the exposure was very hit or miss (usually miss!) and often the suggested exposure would be several stops over (if time is a factor I often go with auto-bracketing five images). The close focus capability was pretty good, and I got some nice images of flowers with f/4 being a good compromise between depth-of-field and nice out-of-focus areas. If I needed to get closer, I used my No. 1 extension tube. Much more than that and you find yourself very close to the subject and hard to adjust the light.
Now that the month is over, I've moved on to using the K150/4 which is quite the contrast. Last month's images are on my Ipernity site here:
ipernity: Single in September 2020 by Kris Lockyear (rather than flood this thread with images). There are two things I now want to do. Firstly, I am planning to use it for a roll of film to see how it performs with the medium it was intended for. Secondly, I'm keeping my eye out for an original lens hood! The only one I have seen for sale so far was about a 1/4 of what I paid for the lens.
Best wishes, Kris.