just buy the canon 400 mm F 5.6 I've owned one for years and it does everything you want very well and more.Even bored at work the other day I used the 400 mm for half an hour and nailed a cover image for outdoor magazine,see image,and its earned another $250 for little effort.Its a light easy to use lens,last night used it to image the current comet.(see other thread)
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