I do not understand how guide numbers are derived, but I do know that a higher number is a higher output... But I still cannot understand the difference here.
Niloyd wrote:
that makes sense, so you are sure about this right?
Yes.
Furthermore this is also a conservative rating at 35mm. Most other flashes rate their GN at the highest focal length (most focused) setting in the fresnel zoom range to get the highest rating. The CT45 does not have a zoom head so there is only one GN rating. But the MZ76 does have a zoom head like most speedlights and it is rated at 76 meters or 249' even though it is the same power as the 45 at 35mm, as the MZ76 specs show:
107' (32.5 m) at 20mm
128' (39 m) at 24mm
138' (42 m) at 28mm
149' (45.5 m) at 35mm (METZ 45)
177' (54 m) at 50mm
213' (65 m) at 70mm
228' (69.5 m) at 85mm
249' (76 m) at 105mm
Flashes like the Metz 58AF-1 or Canon 580 are rated at GN 58 meters or 190' at 105mm, but at 35mm (same as CT45) they would only be about 114' or 35 meters.
About a stop difference.
The most confusing thing when figuring GN's is that rest of the world uses metric to rate, but to get actual working f-stops you need to convert to imperial. Go figure.
