Well, I was afraid this day would come - luckily I'm gonna rent whatever is decided! I have an opportunity to go with some volunteers to photograph critters/birds while they document them. I'm thinking I need a longer lens but don't know what! Should it be a zoom lens with a fixed aperture? Or should it be something like a 600mm or bigger? I have both a 1.4 and a 1.7 TC but hope to not use one or any of them because I hope to get my best photos ever! As of now, my longest lens is the 300mm afs f4. I'm open to suggestions! I'm thinking about getting a bean bag for shooting from the van. I don't know if my tripod will be enough for a big lens!