[ajuett]

I'm on LBA on the cheap for now. I picked up a excellent condition Pentax-A 200mm f/4 with a T6-2X TC today. I don't have any thing decent photo-wise to post as it was mainly find the setting which kills the PF.

Without the TC on, f/5.6 and above on my copy handles PF well enough that I think its acceptable. I had an M 200mm f/4 about 2 years ago that was unacceptable even up to f/8, it must have been a really bad copy. This A series lens is very sharp.

With the TC on the PF at f/6.7 is about the same result as without at f/5.6. The 2 issues are; 1. it passes infinity focus and 2. the focus indicator doesn't help as much.
Focusing, therefore, is not that easy. Also, with the TC on it stops the lens from metering but, that again is not a big issue with me. With the TC on its not as sharp as without but that is a given.

I think I'm going to like the A 200mm f/4 by itself. For handhold ability and the A position it's more realistic for me to get more keepers.

[reeftool]

With my older glass, I've found that PF is more of an issue with the particular light and contrast of the shot, not so much the f stop. I agree that using a TC can make things worse. It seems to be at it's worse on somewhat light overcast days when it's still bright but a white sky. It's definately not the lens to choose for birds or squirrells in the tree tops.