I'm looking to get these two lenses for a pretty nice price from someone unloading their old "junk" and may sell one off once I've gotten to try them a little. I'm curious what the conventional wisdom is about a TC for one of these is. Did Pentax make one specifically to go with one of these? Like the 1.4 maybe? A quick look at eBay and there are tons of cheap 2x converters (I already have a Vivitar 2x that is so-so) and a handful of 1.4x or 1.7x TCs from Pentax and Sigma that are going for a LOT ($450-550) of money! So I'm thinking those must be the good ones and they are in high demand. I think I will probably just try them on my Vivitar and see if it's acceptable for the time being if I want to go longer. Anyone got any more info or leads on better deals? Thanks!