For what it is worth here is the 'quick and dirty' fix I have carried out to hopefully reduce the problem. I used a bit of electrical insulation tape, rather crudely cut with a pair of kitchen scissors, as you can see

The close up shows the mark on the tape where the 70-200 rubs when being mounted.

I only have one Tamron, the 10-24, and that's fine. A bigger lens like the 70-200 would be interesting to try. The Samyang 85mm is also fine, and that's a fairly beefy lens.

Send a needle file in the post so we can make a neat groove in the housing to save the lens doing the hard work? While waiting to see what Sigma come up with I may just stick a small strip of masking tape on the base of the housing to protect it.

Thanks for posting this. I have just checked my 70-200, which I think is one of the lenses listed (it's the OS HSM version but I don't see a 'II' on it?). The clearance between the lens and the base of the viewfinder housing is very tight, less than 1mm, but it does not actually make contact. I think it could rub when mounting the lens if care is not taken with alignment.

Give the 'pro contrast' filter a go (within the Colour Efex Pro segment). Very good for breathing life into dead images.

If you do not mind buying used lenses then you do not have to dig so deep. Over the past 18 months or so I have purchased a set of good examples of recent F/F Sigma zooms - 12-24, 24-70, 70-200. All very capable lenses. The combined cost was less than £1200. I already have some nice Pentax F/F primes.

The new releases do seem expensive although they will no doubt get cheaper in time. They are also quite big and heavy compared with some of the competition, which is unusual for Pentax.

Thanks for these shots John. In case anyone thinks that using crop mode on the K1 is going to give disappointing results, it doesn't. I have been comparing results using DA 21 and DA 70 in crop mode on the K1 with identical shots taken with the same lenses on my K5II. My first efforts showed the K1 shots to be noticeably crisper. I put this down to perhaps improved SR and no AA filter. I have since carried out further tests under more controlled conditions - SR off, tripod, mirror up remote - and both sets of shots are as near as I can tell identical, however closely I examine them.

Please disregard this comment. I have now tested out the crop mode using some primes and it is correct.

Just tested all my Sigma lenses on the K1 (18-35, 17-70, 24mm, 24-70, 50-150, 70-200, 150-500) and they all work except the 150-500 APO HSM which refuses to focus even with the contacts cleaned (and it thought it was a crop lens). Conversely it thought the 17-70 was a full frame.

I have just tried my Sigma 70-200 APO EX DG HSM (most recent version I think) on my K1 and it works fine. My mode dial is working as it should. My main concern so far is that the output looks bland compared to my K5II. Taking the same scene on identical settings the K5II outputs typical rich 'Pentax colours' , the K1 gives a more muted result more reminiscent of canon. This may partly be because it seems to give about a half stop extra exposure than the K5II, producing a perfect histogram but a rather flat result for my taste. I will have to tweak the settings to get it to my taste. My other observation is that crop mode is a little smaller than it should be but I was testing using the 16-85 zoom so I may have inadvertently nudged it while changing bodies. I will try again using a prime when I get chance.