I had the chance to do some extensive shooting over the weekend with the Sigma 150-500mm and this is my observation.
- Most of the shot I took were between 400-500mm.
- F8 is the way to go. This should not be a problem for more modern camera. Bump the ISO.
- OS is extremely usable. I handheld every single shot
- AF can be slow at time.
- The zoom ring is a little rough
As I was walking looking for birds at the local sanctuary, I met lots of birders/photographer. The 100-400L was really the most common lens uses. It was everywhere. People stop me by and ask me what I was carrying. All of them said the same thing : I would kill right now for an extra 100mm, it must be nice.
I have 2 more days to decide If I keep the Sigma or fork more dollars and trade it for an 100-400L. After reading numerous forum threads, I am leaning toward keeping the Sigma. I got some more then acceptable quality image and a good experience overall. This is surprising as my first experience with the 120-400 was terrible (I must of got a bad copy).
At the end of the day, photography is more about composition and framing then anything else. As I was showing my photos around the office, they were talking about the subject not about sharpness from corner to corner. It easy to forget when you get caught up in the internet propaganda.