I have the kit lens, plus Panasonic 14mm/2.5 pancake (to turn the PL1 in a very compact shooter). Now I was thinking at something to have some long reach, let's say about 500/600mm equivalent, or more, but keeping it cheap & small. I would like to try & experiment a bit with a catadioptric lens. I see lots of them on eBay, but I don't have much an idea about how to orient among them. Is there some model to recommend, that could be considered a "cheap best buy" of sort? Thanks!