A client contacted me last week.  She was finding that her existing telephoto zoom lens did not have the reach that she needed for birding, and had done some initial research and was interested in Sigma's 150-600/5-6.3 Sport telephoto zoom.  She wanted to know if I had shot it and tested it before ordering one, because while priced competitively, they are not inexpensive.  To learn what I discovered, read on...