I am a Nikon user, I take bird and nature shots, my progression was
Nikon 70 300mm f4.5/f5.6 VR zoom …… new
Nikon 300f4 …… mint used
Nikon TC14Ell ………. new
Nikon 300mm f2.8VR ….. mint used
Nikon TC20Elll …….. mint used
Nikon AF-S 600mm f4 (non VR) - I could not/did not want to spend the money on the VR model …….. vgc used
I still have all the above and use them all depending on the circumstances … I use the 70 300mm on the river from a canoe
What would I also buy, maybe a Nikon 400mm f2.8VR ….. as it is just a sweet lens
I was thinking about the new 80 400mm VR Nikon zoom …… cost for lens only is up to £1,750 new ……… because I spend just over a month in S Africa each year and I want something that I can take as hand luggage with all my other kit, in the past I have taken the 300f4 and TC14 with tripod wise a light weight Redged or similar…. not my Gitzo,
BUT for that money I can get the Canon 400mm f5.6, the Canon 1.4TC and a Canon 7D body ….. which is very good, lightweight and will give me almost 900mm if I need it … OK the fvalue will be high but light is not usually a problem in summer in SA and I will have a tripod if needed.
I do not like zooms, just my opinion
It is a never ending "gear game" with Bird photography … tripods, gimbals, etc, etc, as well as lens ……. but IMHO these are as or more important than the body ….. provided you have a reasonable body ………. my D300 still takes great shots ….. but the crop factor of the D7100 is handy and the quality of the D700 can be appreciated
Go for a prime that you can carry around, if needed, to start with