[joekid]

ive used lots of converters in the past 20 or so years, and the latest one on a sigma 400mm 5.6 apo lens,the lens was great on its own ,i tried the 2 times sigma apo version but it didnt quite have the edge on selective enlargements, so i tried the 1.4,which was lots better,and with good film gave good results,you need to use a firm tripod, for best results,and remote release/if your camera has mirror lock up use that too(if quality is the thing) but ive used it gently pressing the release with good results, the more you pay the better the results,, do a little home work before parting with your cash ,, good luck fella.