[pjgoswami]

Presently I am using a AF-S DX NIKKOR 18-55mm f/3.5-5.6G VR (3.0x) Lens & Viviter 200mm telelens (Manual) with my new Nikon D5000.

As crop factor from 35mm film camera to APS-C(DX) is about 1.5 so I am getting 300mm(200mmX1.5) for the Vivitar 200mm lens. Now my confusion is that if I will buy a Nikon 70-300mm Telelens whether I will get 105-450mm (when used with Nikon DX format digital SLRs is equivalent to a 105-450mm on a 35mm format SLR: Nikon site) or the actual 70-300mm.

My confusion arises after reading a line in the Book "Nikon D60 Digital field guide" Chapter 5: Selecting & using lenses. Page no. 92. "Camera and lens manufacturers went to work creating specific lenses for DSLRs with digital sensors. These lenses are known as DX format."

As per the books which are the DX lenses.

If I will get 450mm at extreme end for 70-300mm lens then I can start shooting birds by that lens after purchase for the time being, but suggested lens starts from 400mm & which I can't effort now.