Correct your lens and lose the colour

Open a raw file you want to convert to mono into Photoshop CC, or use Wells Steps.NEF from the Resources folder. Photoshop will recognise it’s a raw and load it into the Adobe Camera Raw (ACR) interface.

To begin, make sure it’s the right way round by pressing L or R to rotate it, then click on the Lens Corrections tab (Ctrl/Cmd+Alt+6). Tick the Remove Chromatic Aberration and Enable Profile Corrections boxes. This will fix any fringing, distortion and vignetting caused by your lens. Now go to the Basic tab (Ctrl/Cmd+Alt+1), and move the Saturation slider to -100. This will remove the colour and give you a mono image.