I presume these are crossed polarisers, which will go from quite dark to very dark depending on the rotation position.

Moved to competitions section.

Time to call a halt. There is no doubt that the examples of using hugely expensive marque TCs with hugely expensive marque lenses will be viable.

Equally there is no doubt that lower cost zoom lenses are generally unhappy with TCs, especially cheap ones.

Creative liberties have been taken, but over-reaction to them is not helpful either.

There has always been talk of major marques making lenses for each others' camera bodies, but it very rarely happens.

The last ones I have seen were actually Pentax lenses made for Leica rangefinder bodies.

There's no Holy Grail out there from other makes that would make one jot of difference to the end result. All the marques are excellent, all have some lesser lenses that soon disappear.

The more sensible approach IMHO is if you actually do need an 85mm f1.2 lens then you buy into a camera system that has one.

Excellent, I like your book very much.

You can replace the screen with the genuine Pentax part.

This sort of thing is quite common and usually the result of using a wide angle lens at an off-square angle, ie., pointing up or pointing down. As a consequence you will never line up the two parts of the image. The only solution is to judge by eye what looks right, even though something may well be out of true.

Don't forget that lots of modern zoom lenses are not rectilinear either, so they bend straight lines, especially near the edges.

A possible solution is to use Photoshop Transform>Distort to "correct" the image as you seee fit.

The lens may be misreporting. There's no guarantee that non-Pentax lenses, especially o0ld ones, will show up correctly on newer bodies.

But what relevance does a test of Canon lenses and Tcs have to Pentax Users?

You have seen the multi-coloured K-x and the interchangeable fron RS1000 and RS1500? It comes very close to what you are saying.