Canon EF 28-300mm f/3.5-5.6L IS USM Lens ...Alternatives?? Hi, I am one of the owners of 3dskylines.com. I do a lot of helicopter photography and I am eyeing to buy the Canon lense listed above. The reasons are obvious why I need a lense like this... fast focus, image stabilization, quality, and flexibility. I often fly with the doors open and sitting on the edge of the helicopter so changing lenses in the air is not an option. I know this lense is a beast but weight is not an issue since I often use a monopod on the heli. The question I have is, is there an alternative or one that is close to the functions and features of this lense? Before I plunk down $2100, I would love to hear your recommendations. Thank you.