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<blockquote data-quote="480sparky" data-source="post: 229884" data-attributes="member: 15805">The focal length of a given lens does not change.&nbsp; When designing a DX lens, however, it only needs to cover the smaller area of a DX-format sensor (usually 16x24mm).&nbsp; A 50mm FX lens would need to cover a much larger area, 24x36mm.What will change, when using focal lengths that are the same, between the two formats is the resulting field of view.<img src="http://i214.photobucket.com/albums/cc172/480sparky/Photography/FFvCropNewSmall.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" />The lens doesn't crop anything.&nbsp; All it does is pass the light that hits the front element on through to the back end for the sensor to 'see'.&nbsp; The lens is ignorant of whether it's on a DX or FX camera.&nbsp; It doesn't need to know anyway.The cameras do, on the other hand, may need to know whether the lens is FX or DX, but only the FX bodies.&nbsp; This is because every Nikon FX body ever made has a DX-mode funtion to allow it to shoot with DX lenses.&nbsp; In this scenario, the FX body can either manually or automatically detect a DX lens and shoot in DX mode, or be set to shoot in DX mode even with an FX lens (sports &amp; wildlife shooters do this quite often).</blockquote>

[QUOTE="480sparky, post: 229884, member: 15805"] The focal length of a given lens does not change. When designing a DX lens, however, it only needs to cover the smaller area of a DX-format sensor (usually 16x24mm). A 50mm FX lens would need to cover a much larger area, 24x36mm. What will change, when using focal lengths that are the same, between the two formats is the resulting field of view. [IMG]http://i214.photobucket.com/albums/cc172/480sparky/Photography/FFvCropNewSmall.jpg[/IMG] The lens doesn't crop anything. All it does is pass the light that hits the front element on through to the back end for the sensor to 'see'. The lens is ignorant of whether it's on a DX or FX camera. It doesn't need to know anyway. The cameras do, on the other hand, may need to know whether the lens is FX or DX, but only the FX bodies. This is because every Nikon FX body ever made has a DX-mode funtion to allow it to shoot with DX lenses. In this scenario, the FX body can either manually or automatically detect a DX lens and shoot in DX mode, or be set to shoot in DX mode even with an FX lens (sports & wildlife shooters do this quite often). [/QUOTE]

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