I attended an excellent presentation by an accomplished local bird photographer who uses a Nikon D300 with Nikon's 200-400mm f/4 lens + the 1.5x TC. The lens will autofocus with the 1.5x TC and he stated that for a local lake and species of bird he shoots (grebes), that he absolutely needs the 1.5x TC on his lens.
I shoot with Canon and have a 400mm f/5.6L lens and a 7D. Obviously I cannot use my 1.4x TC and expect to autofocus.
It just came to me that when I first worked in photography, I did not have a camera/lens with a built-in rangefinder. Instead, I guestimated the distance and set that on my lens.
Obviously, I wasn't shooting with a 400mm lens wide open at f/5.6 which produces rather thin DOF.
Getting a 500mm or 600mm lens is price prohibitive. for me. IMO, the ideal lens for birding and general wildlife would be the new Canon 200-400mm f/4L IS 1.4x but, I really don't want to sell my kidney for the price of a lens. Possible, one of the big Sigma lenses would do the trick but, that would still mean a considerable expenditure.
I am wondering if an auxillery rangefinder such as this might not do the trick for a little over a hundred bucks...
http://www.amazon.com/Wildgame-Innov...7608837&sr=8-9
I could find the distance of my subject and then manually select that distance on the distance scale of the lens. Obvously, it would be slower than an autofocus lens and I probably could not use it for birds in flight but, it might be just the trick for swimming and nesting birds.