>>2912611I have the 50-500. It is big, heavy and not that versatile as your 55-300. Actually I am in the market for an HD 55-300 as a lightweight most time carry telezoom. That or waiting a few months and give up on some of the lightweight attributes and get a DA* 60-250.
Back to the Bigma, it has excellent IQ, great pseudo macro at 200mm (pic related) and effective OS though not as good as the in-body SR even at 400mm. Oh and it is useless to go beyond 400mm because the image gets soft(ish) after 300mm with 400mm retaining most of the sharpness but quickly degrades at 500mm.
Don't expect it to bring far away stuff closer, you need the subject as big as 3x3 AF points to track with confidence though when the tracking locks it tracks well. Did I mention it being big and heavy?
Also there is not much difference between 300mm and 400mm, the difference between 200mm and 300mm is much much greater. So only consider the Bigma if you want the big zoom versatility, otherwise you are better off with a 300mm prime, maybe with a 1.4x extender.
Also no weather sealing on the Bigma which should be considered if you are living in a temperate region near hills and forests
