I am thinking of a budget alternative for bird shots. I have a M4/3 converter to Nikon, and am Ok with an all manual lens. A fixed 300 to 400mm lens would give me 600mm plus effective length. If the lens is tack sharp, I will be happy to back away from the subject. I am using and very happy with an older Micro Nikor for macro, which cost less than $200, so hope for a repeat experience, optimist that I am.