Best telephoto lens > 50mm to with nex 7, Auto focus is optional

Hi,

I'm looking for good telephoto lens for my Nex 7. Currently I have 16f2.8, 18-55(kit) and 50f1.8 all from sony, I need a good telephoto lens. Auto focus need not be necessary. Any mount is welcome, but a good lens in budget of less than $600.

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Thanks
Himas