Crop factor on Nikon DX lenses?

I know that if I buy an FX/full frame lens for my Nikon DLSR with an APS-C sensor, then there's an approximately 1.5x crop factor applied, so that a 70-300MM FX lens attached to a DSLR would actually have a zoom range equivalent to about 105-450mm.

However, if I buy a 70-300mm DX format lens, which are specificly made for APS-C cameras, does the crop factor still apply (thus still producing a 105-450mm range), or is it a true 70-300mm?

The crop factor applies regardless of the lens type. So a 50mm lens will have an "apparent" focal length of 75mm regardless of whether or not it is a Fx or Dx lens.

Realize however that the focal length change is only "apparent" and not true. The measurement of focal length is from the focal plane (where the sensor is) to the optical center of the lens when focused at infinity.

And since the focal plane to lens mounting flange of both Fx and Dx Nikons are identical, the true focal length is the same regardless of whether or not a Fx or Dx lens is mounted on a Fx or Dx camera.

As well, when you use a given lens on a Dx camera, you have to back up to get the same view as that same lens on a Fx camera. Backing up however increases DoF. So when using a lens on a Dx camera, the apparent focal length increases, but the DoF also increases, which is opposite of what should happen (the DoF should decrease).

That is why using lenses on a cropped camera should be considered an "Apparent" focal length shift, and not a true focal length shift.

To understand this all, just think of taking an image produced in a Fx camera and cropping it by 0.667x (1.5x crop factor). Essentially that is the difference in Fx and Dx cameras.

Truth be told, to make a Dx lens… At least conceptually, you could just put a Fx lens into a lathe and turn down in diameter as it does not use the entire lens surface - just the center 66%. That simply results in a smaller diameter lens, but the focal length is identical