What was it priced at, out of interest? I have an M42 copy and it's a great lens, lovely to use.

I too got both of these lenses from the same vendor in a purchase a few years ago. The 50mm is great and the 28mm is very good from f/4 (though has horrible bokeh).

I have to say this is a big blow to Pentax, despite what some say. They provide some lenses that have been very popular indeed (17-50/2.8, 10-20 etc) and which don't really have an equivalent from Pentax or another third party make, die to either significant price or quality differences.

I think the recent announcement that a flagship APS-C camera is in the line is an attempt to show they're still interested in APS-C, but a new flagship is looking overdue, the KP has been generally over-priced and the K-70 is a looking a little long in the tooth as well as suffering from aperture block failures. It's a pretty poor show currently from Pentax in APS-C cameras.

I'll take the Vivitar 17mm please, and will give some thought to the K 24mm.

I have a cheap CPL (67mm I think) I used on the first day in San Francisco a few years ago on my Tamron 17-50mm. The pictures were awful: poor contrast, dull colours and a slight drop in sharpness (though that could have been my perception due to the first two issues I mentioned). I took it off and pictures were much better.

The problem with this is that the lens hood will probably no longer fit over the large filter and stepping rings.

I have a 49mm Marumi CPL which is superb - I use it on my DA Limited lenses with no visible image degradation. I think mine is the smaller version of this one (Super DHG): https://www.amazon.co.uk/Marumi-Super-circular-polarising-Filter/dp/B001F7BFMY/r...=sr_1_6?keywords=62mm+marumi&qid=1567671574&s=gateway&sr=8-6

But there's a cheaper "slim" Marumi CPL here which has excellent reviews (though not many of them): https://www.amazon.co.uk/Marumi-Slim-62mm-Circular-Filter/dp/B00NXT41VO/ref=sr_1_2?keywords=62mm+marumi&qid=1567671574&s=gateway&sr=8-2

When I opened the thread and saw the top of the first image I though it'd be a nice scenic landscape but then I saw the whole thing

That's certainly my favourite from these, excellent timing.

I have eye (and face) AF on my Fujifilm X-T20 and it can be very useful, though a little practice in focus and re-compose on my K-3 produces almost identical results and doesn't have the side effect of focusing on a face when I don't want it to.

The 16-50mm is indeed known for poor quality control as well as the SDM problem. It's not a lens with a good reputation and if I were you I'd take it back.

I think the KX is the only camera where that's needed to make the meter work.

This has worked for me on MXs before. Sometimes a thin layer of dirt and/or rust prevents the current from flowing. Also make sure the batteries are in the right way around.