Nikon D800 with 135mm f/2 DC prime lens
Freezing motion in the still image is actually a very simple concept - we just require a fast shutter speed. How fast you ask? That depends on what we are trying to freeze in the frame. For fast moving objects with longer lenses, generally we are going to need shutter speeds of a few thousandth - 1/1000, 1/2000 etc and upwards. If we are talking about someone walking, depending on the subject to camera distance, lens etc, we might only need 1/500 even on a high resolution sensor. Let’s look at the example above shot at ISO 100, f/2, 1/3200. If we look at a close up we can see more clearly. The depth of field at this close range with a large sensor such as the D800, we can see the the plane of focus is very fine (it’s on the eyes of courser, however at the bottom left of the picture, water droplets come close into this plane, hence appear sharper). This is a good example to illustrate that everything is perfectly frozen here; but some of the droplets are within the depth of field more than others. I could have gone even faster here with my shutter speed if needed. (I could do that by simply doubling the ISO to get double the shutter speed).
I am shooting in aperture or manual with all of my work. Aperture is a great mode because it allows conscious control of aperture and therefore the shutter speed (by simple knowledge that opening the aperture will quicken the shutter speed, and vice versa), however you get a little more help with the onboard computer in the camera than you do with manual mode. This means generally you can react quicker to a changing scene that happens in front of camera. Aperture works so well, because we know that in bright light, if we use a wide aperture, we are going to get a fast shutter speed, even at base ISO. So all it takes for scenes like these is aperture priority mode, the widest aperture the lens shoots at, be it f/1.4, f/2, f/2.8, base ISO and an occasional glancing at the shutter speed readout in the viewfinder. If it drops lower than you want, simply up the ISO (or if possible, open up the aperture). This way of working gives great control, and speed / flexibility. Outdoors with fast lenses, it is very easy to stop motion like this. However, if we wanted to do the opposite - just stay at base ISO and close down the aperture. In aperture mode, the camera will drop the shutter speed (which again you can continually glance at in the finder), and as you get to lower speeds, the water will blur across the image. It all depends on the desired effect. Learning these things until they become intuitive is very important to mastering the craft.