lonestar,
The 1850PRO isn't a very good teleconvertor. It has soft edges, adds quite a bit of CA (fringing/blooming) and is recommended to be used at F5.6 and above. It's OK for a "knock-around" tc. Like for sporting events when image quality isn't paramount. Or, possibly on top of a +4 close up lens for macro shots. Other than that, I'd suggest you look into the Oly TCON17, 14b or B-300. Or, the Sony HGD1758.
I'd also, advise you not to waste your money on the "titanium" krap you see on eBay. They aren't 2X they are closer to 1.4X and the image quality is poor. I don't believe you will find any TC's above 1.7X that yield a high quality image. Out of the thousands of forum posters here, no one has found one, yet.
BTW, I paid $104 for mine @
http://www.bugeyedigital.com
Here's a macro shot, from about 18 inches away, taken using the 1850 PRO on top of a +4 close up
1850PRO squirrel shot
It's not an awful lens. It's just not a real good lens.
Steve
--
http://www.pbase.com/slo2k
'If one really wishes to be master of an art, technical knowledge of it is not enough. One has to transcend technique so that the art becomes an 'artless art' growing out of the Unconscious.'