I am beginning to draw my own conclusions about when to use the Fuji cameras (X-E1 and X100s) and when to use my more conventional SLR cameras. I admire the work of photographers like Zack Arias, one of several high profile advocates of the mirrorless technology. I see the spirit of the "street photographer" in his work, resulting in feeling of a voyeur without any hint of prurience. Photos from a trip to Havana, Cuba in this blog entry captured some very intimate slices of life. Not sensual, but he captures images of things that might normally escape our gaze, or that we secretly want to stare at, but feel we shouldn't.
Unobtrusive: These photos were taken during a letter writing campaign here at the Adult School. I was able to move easily about the room carrying only the X-E1 and its 18-55mm f/2.8-4 kit lens. Aperture wide open and set to its shortest focal length, the lens isn't particularly fast, becoming less so when zoomed to its longest focal length of 50mm. It doesn't have the delineated plane of focus provided by my heavier, but faster, DSLR zooms. But the camera's hushed click was easy for these students to ignore, and it became easy to do followup shots without the distracting "clack" of my mirrored cameras.
Diminutive: The small size of the cameras makes them far less intimidating, a fact that has been proven over and over again in a variety of venues. Its size and feel reminded me of my Olympus 35SP, my first, and last, "daily carry" camera I ever owned. Even my recently purchased 12mm Zeiss Touit lens with its 67mm filters seems so much smaller than my SLR lenses. Mounted on the undersized XE1 body, the combination is almost laughable.
Precision: I consider this both a plus and a minus. To the debit, the small size puts the external buttons uncomfortably close to one another, and I found myself inadvertently changing settings from time to time. To the credit side, make a single photograph became an act of critical focus, literally. While the external adjustments for aperture setting and exposure time were clearly visible from above one had to check them frequently to make sure that no settings had gone awry, which they sometimes did. I was annoyed by the lack of markings on the kit zoom. You really couldn't tell if you had changed your aperture setting unless you checked in the view finder. I suspect I could learn to check my settings on the LCD display before bringing the camera to my eye, but when using a camera that took such pride in its retro layout, it seems awkward, and illogical. I do understand that a properly marked aperture ring would be problematic, since the current offering of zoom lenses have variable maximum aperture settings (remember the F 2.8-4 spec on the kit lens?). This shortcoming does not apply to the prime (non-zoom) lenses.
Focusing: I found this to be a little annoying. First off, under some conditions, the electronic viewfinder was not as responsive as a mirrored reflex camera. Certainly the efficiency has increased dramatically since the days of the Sony R1, but isn't up to the level of a current DSLR. And while the general layout of the viewfinder was logical for a former rangefinder shooting like myself, the focusing sensor, located where the split-image ranger finder used to be, didn't seem to adapt to the focus/re-compose sequence I've become accustomed to. And while its location can be moved, you must take the camera from your eye because there isn't enough space between the back of the camera and your cheek to "feel" the adjustments. Perhaps it's the barely perceptible blurring that inevitably occurs when the camera is repositioned during the final phase of composition, but there's definitely something bothersome about the view.
This shouldn't be confused with sensitivity, however. I've gotten sharply focused images in situations where the low level of existing light would have given most SLR conniptions. The Fuji could lock focus on the proverbial "black cat in a coal bin", but it took a while to do it.
For right now, the Fuji seems to be at its best when shooting available light indoors. If the "stealthy photographer" approach is required, the nearly silent, mirrorless wonders will certainly fill the bill. But be prepared to shoot slowly and with great deliberation.