My only point was the fact that the lens is designed for FF sensors makes no difference to the field of FoV. That was in response to this:
Which makes it sound as though a 70-300mm DX Lens would not act as a 105-450mm lens. It makes no difference what the image circle of the lens is (FF vs crop), they all act the same giving the same FoV at the same focal lengths.
It is also misleading to say the lens acts like 450mm because the focal length is just a physical measurement from the front element to the sensor plane. What is true is you would need a 450mm lens on FF to get the same FoV, provided you don't crop the image, so that is why people say that but it isn't that simple. You really need to consider the pixel density of the sensor because if the FF sensor has the same pixel density as the crop sensor then you can crop the FF image to DX size and get that exact same "450mm equivalence" despite being a 300mm lens.
What tends to be the case until the D800 came along was that FF sensor had much lower pixel density which meant there was the very real problem of having less subject details using the same lens on FF than on crop. Even now though you get 24MP on crop so it all gets pretty confusing. What you a are really interested in is how many pixels will I get covering a certain subject of a certain size at a certain distance using this lens on this body. My new D800 gives me more pixels (15.5MP DX crop) on a distant bird of prey than my D90 (12MP) using my 300mm f/4.0 despite the the D90 having an "effective 450mm" vs 300mm on the D800. So effective focal length is misleading here.
