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Sorry if this has already been covered but I'm a bit of a virgin with DSLR's. I have a Nikon D7200 DX Body with a couple of kit lenses. i have recently aquired a Nikkor AF-S 70-300mm 1:4.5-5.6 ED IF which is an FX lens. All the info suggests it should perform as a 450mm on my DX body but ... The focal length and recorded image look exactly the same as my 300mm DX kit lens. Am I missing something ?