New to photography… I have just bought a Nikon d7200, with a sigma 18-35mm f1.8 lens; I had also purchased a Nikon 35mm prime, 1.8, but sent it back because I realised that I have already covered this focal length with the sigma. Shall I get a 50mm instead, which will be around 70mm on my crop sensor camera - looking for a portrait lens and something more naturally suited to shots that mimic the human eye. In advance, I thank you for all advice given.