April 16, 2012.  Here is a short take on the EF-42 flash that fits various Fuji cameras (including the X100 and the incipient X-Pro1).

Five functional points

First point: buy one used ("warehouse deal") from Amazon. Paying $20 more for a completely new one won't enhance the experience much. This is a basic TTL flash made by Sunpak (PZ42X) that is normally Sunpak-branded and available for Nikon, Canon and Sony. It's the size of a DSLR flash (i.e., pretty big for either the X100 or the X-Pro1).

Second point: it works very, very well. The Fuji TTL system has an almost instantaneous preflash (shame on you, Leica digital TTL...), and the system delivers a "full" histogram that only drops down about 80% of the way to the right. In other words, nice, bright and correctly exposed pictures right out of the box. You may want to up the exposure compensation on an X-Pro1 by about 1/2 stop (if you use the flash) or 2/3 stop (if you do it on the camera). Note that these settings reset to zero when you turn off the camera or flash.

Third point: tilt/swivel capability is impressive, but this flash needs a diffuser dome. The camera can bounce off the ceiling in virtually any orientation (so long as you are not blocking the reflection...), and the flash mercifully omits the annoying bounce/swivel squeeze lock on most of the units made by National (Panasonic) for other camera companies. Recommendation - tape the diffuser dome for a Nikon SB-800 onto the flash head.

Fourth point: the controls are terrible. The same "mode" button cycles through EV compensation, 35mm or digital format, and zoom setting. EV compensation has no up and down buttons; you press "Mode" to toggle positive and negative and "Select" to change the value. Whether you set these values on the flash or on the camera, they are inoperative with Auto ISO. The usefulness of the auto-zoom is yet to be seen, though it does change automatically on the X100 and X-Pro1.

Fifth point: the display is ok. Everything is laid out properly, there is a handy interactive usable distance scale that changes with the zoom setting, and the backlight (red) is automatically activated by changes in the swivel/tilt setting (but oddly, not by ISO changes).

The overall view

In terms of fluidity in use, it's easy with either camera. The flash controls on the cameras work seamlessly, though the flash basically runs only in (M)anual with power factors or (TTL) mode.

In a lot of ways, this feels like a pretty shameless port of the Sunpak version, with many vestigial features. First, there is no "35mm" Fuji camera with this pattern hot shoe (shared with Canon and Ricoh) - so the whole range of "35mm" zoom settings is unnecessary. Second, the AF illuminator does not do anything (one day it may with a firmware upgrade from Fuji). Third, the hot shoe locking mechanism is a knurled friction ring, not the drop-down retaining pin common on all modern cameras. This ring is of a large enough diameter that it blocks the view of the X100 shutter speed dial (whose setting, fortunately, is visible in the viewfinder).

But do you care that it's a port? There are not a lot of real flash options for the X100 and the X-Pro1. The EF-20 has half the power, sits close to the film axis and flips up in only one direction. The EF-42 generates nicely balanced, "real" flash pictures worthy of the cost of these cameras.