Originally posted by clickclick Yep, this is important to remember. It's really easy to get sucked down the rabbit hole of thinking you need edge to edge sharpness for a great photograph.
The problem with the old 2.5/200mm is not edge sharpness (which is often unnecessary, in my opinion), it's the strong fringing.
I won one quite recently, then the seller canceled the sale
I would be happy to have one for collection, it's still a nice lens (given the right lighting) but I believe it's nowhere near the the A Star.
According to my personal experience with vintage tele lenses, 200mm was a more "difficult" focal than for example 135mm.
There are very old preset 135mm's that show little fringing and very good sharpness across full frame format (but the corners).
Most of the more recent 200mm lenses without special glasses are definitely more problematic, especially concerning CA.
The best 200mm I have is... not a 200mm
It's the Tamron 2.5/180mm "Anniversary". Even better than the A Star.
Second best the Pentax-A 4/200mm (different from K and M versions, and with a more advanced optical design).
Regarding the S and L 1.4x converters, they are both very good and well worth buying, if you have Pentax-A tele lenses and you can find them at a decent price.
Of course the L version can be used only with specific lenses because of its shape and optical optimization.