Does anyone ever consider what they are shooting and how much DOF they will need. 30mm/f1.4/10 feet on a crop only has about 1.5 feet DOF, which means you can usually only get 1 person in sharp focus. Now, if you have no choice (either that or no shot), then you have no choice but keep in mind DOF.
I agree. Many people fail to realize this fact. In the setting described f1.4 would not be a good choice for the picture taking aperture as most of the scene would be out of focus. f4 or f5.6 would give better DOF and more keepers. Bump up the ISO to maintain adequate shutter speed. The benefit of a fast lens e.g. f1.4 or f1.8 is that in low light the view finder image is brighter and the camera's AF system performs faster and more accurately locks focus (pressing the shutter button half way down). Then pressing the shutter button all the way down camera then "stops down" to the actual shooting aperture that has been selected which should be based on the required DOF in the scene amongst other things. Also, optical performance in the best light conditions of the 50mm f1.4 at f1.4 is not very desirable unless you want a soft dreamy look.
