I was going to post this pic in my thread about my new 300mm lens but I'm doing it here instead.
Now this is the Vivitar TX 300/5.6 with the Pentax A-2X-S teleconverter shot wide open on a cloudy day at ISO 1000 on a tripod.
Lowell, if you see this, this lens does not have ca, it has CA! So bad that if you try to shoot a bird on a branch with the sky as a background you can see heavy CA, IN THE VIEWFINDER, lol, I'm not kidding. It turns any branches reddish purplish or in some cases, greenish.
BUT, on the other hand, there is something about this lens and, I admit, maybe I'm rationalizing this to justify my $38 purchase:-).
This combo isn't for pixel peepers by any means but there may be a use for this lens.
This is no award winner, for sure, and I'm hesitant to post it here among some truly great photographs in this thread but check out the 3D effect here: