Flash light is only useful when it's actually included in the photograph. Therefore, more advanced flashes feature motorized zoom reflectors which automatically narrow at greater focal lengths. This directs more of the flash power directly into the field of view. This can be very significant: there's typically a 3× effective gain in power from 24mm to 85mm.
All auto-zoom flashes listed here begin at 24mm in 35mm terms, but Pentax and the Tumax DPT3 series stop at 85mm, while the rest go to 105mm. See the guide number table for details on how this affects flash power at higher focal lengths.
Note that the Promaster 7400EDF is missing the typical 28mm and 70mm zoom steps.
The Promaster 5750DX has a zoom reflector, but it isn't motorized or automatic. Instead, it can be set physically to 35mm, 50mm, or 85mm. The Metz 36 AF-4/AF-5 also has a manual zoom reflector; it can be set physically to 28mm, 35mm, 50mm, or 85mm.
The Sigma EF-530DG ST and EF-610DG ST have the opposite deficiency: the zoom is motorized, but only automatically adjusts itself based on the information from the camera. You can't change the zoom manually if you want a wider or narrower beam. The Sigma Super versions do allow a manually-set zoom position.
The Tumax power-zoom flashes automatically zoom with focal length, but the coverage can also be controlled manually.
