I've lost count of how many 28mm and 50mm lenses I've got not
just Pentax..... Vivitar, Sigma, Ensinor, Porst, Chinon, Yashica,
Tamron etc.

Nearly all online retailers have now changed their T&C to
state that a contract doesn't exist until they dispatch
the item. This follows the mistake Kodak made a few years
ago in ludicrously pricing cameras on their website and
having to honour all orders.

Hoover obviously made a mistake a few years ago giving free
airline tickets to the US with every vacuum cleaner sold
and people were buying vacs just for the tickets. They
couldn't get out of it and eventually had to sell the UK
business to Candy

You can get an idea what I'm talking about from this post. link Look at the "1:1 (100%) RHS of frame Compare captured by a screen grab at 800 wide." = RHS of Bridge shot by Chinon 28mm. The bridge was 40-50m away I was square off it and focused on the centre. The RHS of the Chinon shot is very soft. I've not retried it with this lens, but I did with another lens. It was soft as well when focused on the bridge, but when I set the lens to infinity, the centre stayed in focus and the edge went a lot better indicating a massive field curvature. The curvature now being close to infinity.

You can see this on most distant landscape shots with a 28mm sharp in the centre at a distance, but soft at the edge at a distance, but when you look at the edge closer to the camera it doesn't look too bad.

Probably got oil everywhere inside as well I would be surprised if it isn't sticky. If it was about £30 you could just Dremel off the aperture lever and use it as a preset with more accurate metering such as Av

I've had two M 100mm f/2.8's the first which I lost in a stolen
suitcase at Manchester Airport wasn't very sharp, but the one I
have now is, maybe QA was variable on them

The Helios lenses are 58mm f/2 not 50mm

It has been known for "vanity rings" to be swapped

The 28mm isn't a K because it's only got 3 bands of warts
on the rubber grip. The bigger K lens has 5

It doesn't work with 24/28mm lenses anyway.... possibly due to
field curvature. Mattmatic did post a link to an article on the
Phase One site showing how to correctly set up WA lenses on
digital.

It was actually Hardgravity that wrote that

I would be quite happy with "A top quality lens, now in a rubbish condition"

Do you use SR with the DA12-24 Simon? I found it was better without.
I'm quite sure that Nikon and Canon don't have SR in their WA lenses.

Hyperfocal distances were set in the 1930's for large format cameras.... just not good enough for digitals especially on a screen.

I've been trying to sort out 24mm and 28mm lenses recently. They seem to have a massive field curvature which throws things at about 30m on the edge of the frame OOF so the best option seems to be set the lens to infinity as long as it's properly adjusted for infinity. Everything from about 7m to infinity then seems to be in focus and the edges are more acceptable.