Originally posted by Vicioustuna2012
Nah, eBay purchase, and I got a good deal on it. I like it a lot, so I wouldn't do that anyway. Is there a 1.4x TC that would maintain IQ better?
---------- Post added 02-28-17 at 10:31 PM ----------
Why is that? And is there a different converter that would work better?
The problem is a TC costs you light. A 1.4x TC eats up one stop, a 2x TC eats up 2 stops. Not only that, but a TC, in addition to whatever optical flaws it has, also exacerbates the flaws in the lens. So a little bit of softness becomes a lot. That little bit of chromatic aberration becomes a lot. You can still get decent results, but it requires more - and different - post -processing.
That's just IMO, though. I see people post shots taken with a TC that have what I would consider to be bad image quality, but they don't think so. Different people have different standards.
Years ago I went down a path similar to yours, tried various TC's with a Tamron 70-300 that by itself was decent enough, but all of its flaws were magnified by the TC. Not entirely rubbish, but... difficult, and frustrating.
I dropped out of DSLR usage for about half a year, and when I got back I decided that the only way I could comfortably afford the image quality I wanted was to shoot older, manual-focus glass. It doesn't always work out perfectly

but it sure is fun.
Anyway, back to TC's... the best you could get would be the HD 1.4x TC, which is something like $500. And that will take your 50-200/5.6 to 280mm f/8, and that's before stopping down to get the best image quality. A used 55-300 is like $100-$150.
If you don't mind all manual, I found the
Rear Converter K T6-2X Reviews - Pentax K-mount Teleconverters and Adapters - Pentax Lens Reviews & Lens Database to be pretty good. That will take you to 400mm f/11. Here's a trio I took with it combined with a Tak 200/4. The pic of the ducks is cropped a bit, the others are the full frames.