I was confused the other day when I was asked by a fren about crop factor in relation to DOF

Since he is using Nikon D90, a 50mm prime will give him a FOV of 75mm equivalent on an FX (a D700 for e.g), right?

but what about the DOF?

at a given subject distance, the DOF of 50mm f1.4 on an FX is equivalent to 75mm f4.8 on a DX?

I was trying to explain him using the DOFMaster's DOF calculator and it became more confusing to me :embrass:

So, if a 50mm f1.4 prime is used at f1.4 on FX and DX cameras(for a fixed subject distance), what will be the DOFs that are simply given by that lens? Let's forget about the print size (viewing distance).

thanks