hi.. I've been shooting birds using a D300 and Sigma 170-500 for the last 5 years.. The AF in the lens sometimes gives me a lot of head aches.. Still, I was able to capture some good moments.. Over these years, I'm able to approach the birds a lot more without any hides and may be because of that, I'm able to get good pictures of some rare forest birds in poor light with the same lens.. I'm not interested in action shots (may be sour grapes.. hehe) .. So, planning to get an old manual focus 500mm P lens or a 600 f4 IF-Ed lens.. I've done 99.99 birding without a tripod and will try to continue so, though the users of these lenses strongly recommend some sort of support.. Opinion are welcome..
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