I was looking to buy a handle mount flash for a while and while I was rearching guide nos.
I got a little confused...

The manufacturers website for the METZ 45CL1 says that the GN is 45
http://www.metz.de/en/photo-electronics/mecablitz-models/automatic-flash-units/mecablitz-45-cl-1/product-information.html

but the bhphotovideo.com website says the GN as 148
http://www.bhphotovideo.com/c/product/413431-REG/Metz_MZ_45012_45CL_1_Auto_Handle_Mount.html

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.

Can someone help me in understanding this?

45 is referring to meters I believe. (45 meters= 148 feet) Hope this helps.......

http://en.wikipedia.org/wiki/Guide_number

Miner wrote:
45 is referring to meters I believe. (45 meters= 148 feet) Hope this helps.......

that makes sense, so you are sure about this right?

Niloyd wrote:
Miner wrote:
45 is referring to meters I believe. (45 meters= 148 feet) Hope this helps.......

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.

Good luck.

Carmen, thankyou so much and and thanks to everyone else for making time to reply to my query, I really appreciate it!

I have an old Metz 45CL. Really powerful flash. Mines got to be 15 years old I always use it with a Quantum Turbo battery. Highly recommended setup.