Nikon SB-600 zoom on DX body?

When I use the SB-600 it automatically zooms to the current focal length on my lenses. When I use a full frame lens on a dx body for example at 50mm the flash goes to 50mm but wouldn't that be 50mm on FX and it would be more correct if it were set to 70mm? I think the Sb-600 automatically knows if it's mounted on a fx or dx body.

I used to own a SB-600.It can't figure out if it is on a DX or FX body.

At any rate, a 50mm lens is a 50mm lens.

And, when you use a lens on a DX body, it does not matter whether it is a DX or FX lens - the "apparent" focal shift is the same regardless of lens.

A 50mm lens would have the field-of-view of a 50mm lens on a FX body. That same 50mm lens on a DX body would have the field-of-view of a 75mm lens.

That your SB-600 zooms to 50mm on a 50mm lens on a DX body more or less proves it does not know if a DX or FX body is being used.

You need to go to Manual Zoom mode if you want the zoom to be at 75mm with your 50mm lens. But since the field-of-view is tighter on a DX camera, it really does not matter if the SB-600 is set for a wider field-of-view.

The S-700 however, does know if the camera is a DX or FX. But that little difference would not be any reason to upgrade. But if you want to - the SB-600 has a high resale value. I sold my SB-600 used for more than I paid for it when I went to the SB-700.

If the SB-600 sets to 50mm with the 50mm lens in a DX body then it does not automatically recognize if the body is FX or DX. You can adjust the focal length setting manually if you think it's critical. If not, the flash will still fire anyway.