What I've learnt...well
I think the smaller the f number eg 5.6 the more light but can also become too bright and the colour can also be a bit washed out, whereas the larger f number eg f20 there is less light and the pix can be more true to the colour. Of course bigger number sharper the pix. Have I got it right? still doubting myself. If I've got it than I am not sure what to do with the washed out colour especially if you want a blur background.