I have used the Pentax F 1.7x converter with the 300 mm., but I am not satisfied with the results. It doesn't lose too much contrast or sharpness, but out of focus areas when paired with this lens look awful. In fact, that converter yields much better results when used with the FA 80-200 2.8
I am not a pro, neither I need to sell my photos (I wish I could, by the way), so I am interested to know if Novoflex lenses are "good enough" for that kind of photography, particularly the latest Novoflex C and D series, which are said to be better than the classic ones of the 1960's or 70's.
What I won't do is buying another Sigma 400 mm. AF, and I also can't afford an FA 400 mm. 5.6, they are too expensive here.
Carlos

