I had the Big Ma ( 50-500mm).It was an older lens,and didn't have OS.It also liked lots of light and the sweat spot was F8.Good clear pictures if you have a steady hand.For long shots I used a tripod and at 500mm I also used a cordless remote shutter release.If I had the money,the 50-500mm with all the new buttons (OS) is my way to go for shots up to 450mm.Images can get a hint fuzzy over 450mm.I have read reviews on the 150-500 that sound pretty good at 500mm.It's a tough choice,good luck.