
Sigma 18-35mm f/1.8 DC HSM ART, Nikon F DX
Nikon DX, APS-C / DX

Sigma 18-35mm f/1.8 DC HSM ART, Nikon F DX
Nikon DX, APS-C / DX
If I put this lens on my Nikon D7100, do I effectively have the focal length of 18-35mm or do I still have to calculate x 1.5? And can you simply explain when you have to calculate the focal length x 1.5 and when not?