PART 1 laid out the process of considering our creative priorities. Now we look at how the camera fits into it.
What you see is what you get
Mirrorless cameras are fantastic. The electronic viewfinder shows you whatever the sensor sees, so you can make exposure adjustments as you shoot. This puts you in a position closest to the final product: you're able to see and tweak the image as it's being made, and so the image you get at development time should be pretty damned close to what you intended.
Mirrorless cameras generally have awful manual focus, with distracting "peaking" graphics. But the autofocus tends to be excellent in any level of light.
Mirrorless cameras also depend upon a small video screen to show you what the sensor sees. There are advantages to this (like making your X100s into the Fuji Monochrom), but there is a lag, and a video display is a video display—it's not the actual scene.
What you see is . . . well, you see part of what you'll get
Unlike mirrorless cameras, SLR film and DSLR cameras don't show you the final product. "SLR" stands for "Single Lens Reflex," and what it means is that there is a mirror in front of the recording medium (film or sensor) which reflects the light coming through the lens up to a prism box and out through the viewfinder. This means that you're able to see what the lens sees. With film, there's no way to see how the film is being exposed until you develop it. And with a DSLR, the mirror blocks the sensor so there's no way to see the final image.
Although exposure is still a rough mystery, composition is not. You're seeing the image which will be captured, but you'll have to make exposure adjustments in your head from experience. With a digital SLR, you can check exposure on the back LCD display (though this interrupts the shooting process in a negative way).What you see is . . . what you see. What you get is far removed!
Likewise, rangefinders (of which Leica remains the dominant and best maker) don't tell you anything about what the lens sees or what the sensor/film sees. Instead, the rangefinder mechanism is separate from the lens and sensor, and you only see what it sees. If you use a wide angle on a rangefinder, you still only see the undistorted perspective the rangefinder sees, so you'll have no visual feedback on the distortion the lens may be making to the scene. The rangefinder provides no image preview whatsoever other than frame lines which give you a rough approximation of what will be included in the frame. If the lens you're using is more telephoto than the rangefinder optics, you won't get a magnified rangefinder image—you'll get a smaller box of frame lines within the larger rangefinder field of view.
Relieving the GAS Pains
Getting back to my example shooting scenario, which camera will be best for me to use? It won't be the one with x number of pixels. It won't be a particular brand. It won't depend on the latest firmware. Instead, it will be the camera that most closely matches in operation the hierarchy of my creative priorities. When reaching into my bag to pick up a camera, I'm going to want the one that: lets me put my attention on the entirety of the frame.
This means I want a camera that has aperture priority (since I don't really care about the rest of the settings), but more importantly I'll want an autofocus camera since while I'm concerned about selecting a focal point, that focal point is not the subject of my attention.
For the purposes of the example shooting task, a rangefinder would interrupt my creative priorities. A rangefinder needs to be manually focused, and the focus point is small: it takes time and attention to focus a rangefinder, meaning that the focal point becomes a priority which occupies my attention, taking it away from the gestalt of the scene. The autofocus (while somewhat annoying) allows me to pick a focal point and then forget about it. With autofocus, I need not visually confirm focus—I need only select the spot that will be in focus. So in my example scenario, I'll be reaching for the Fuji, and not the Leica.
What does this have to do with behavior? Everything! And that's what we'll discuss in the final part.