Since the guide number at the narrowest reflector zoom setting is the biggest, flash makers like to focus on it, usually working it into product names.
The Metz, Sigma, and Promaster flashes have a reflector which can focus the burst more tightly than the Pentax and Sakar flashes — they go to 105mm (35mm full-frame), whereas the Pentax and Sakar models have zoom reflectors which stop at 85mm. (The zoom reflectors move in discrete steps rather than being continuous, so there's no particular benefit at until you go above the final step.) So, on a current 1.5×-crop Pentax dSLR, if you're at a (real) focal length of 70mm or above, the relative list looks like this, normalized to the Pentax AF360FGZ.
- Metz 58 AF-1 = 2.6×
- Pentax AF540FGZ = 2.2×
- Metz MZ-4i = 2.2×
- Sigma EF-530 DG = 2.1×
- Metz 48 AF-1 = 1.8×
- Promaster 7500EDF = 1.4×
- Sakar 952AF/PEN, et al = 1.4×
- Promaster 5750DX = 1.2×
- Promaster 7400EDF = 1.0×
- Promaster 5550DX = 1.0×
- Pentax AF360FGZ = 1.0× (Of course.)
- Metz 36 AF-4 = 1.0×
- Promaster 7200EDF = 0.72×
- Promaster 5250DX = 0.46×
- Pentax AF200FG = 0.31×
- K20D/K200D/K-7 built-in = 0.13×
- K100D/K10D/K2000/K-m built-in = 0.09×
The number for Sakar is based on their single published figure: their claimed power at maximum zoom of 85mm. Anecdotal reports suggest that the flash is actually significantly less powerful than this in practice. Therefore, I don't recommend putting much faith in it without further information.
