I currently own a d5200, I love the 18-55 but it just isn't fast enough or good in low light, also love my 50 1.8 awesome but not wide enough for so many things. I recently found dust on my sensor and came to the conclusion I switch lenses way too much. I will be moving to FF soon and wonder, what lens would you or could you leave on forever, to cover all situations and not miss any other. I want to purchase that lens and leave it on 99% of the time to avoid contamination, as I am chicken S%&@ and will not clean my sensor. So Everyone, FX, one lens forever, what are you using and why????