hi,

i just got my second-hand flashlight Metz 45 CT-1,  which is an old
dedicated flashlight with guide number of 45/148.   yesterday, i test
it using my Sekonic L508 meter and found there the actual GN is one
stop less than what expected.  my test method is as below,

1) set meter in incident measuring mode and put it in the "d" feet
away from the speedlight and aim it toward the speedlight.
2) set the speed light's ASA dail to ASA 100.
3) put speedlight in manual mode and fire it.
4) got an aperture reading "f" in the meter.

the actuall GN = d * f, that is about 104 in feet and 105 is just
around 148/1.414. i've checked, the "d" does within the range
described in the Metz manual.

what's your opinion about the result?  i guess there are two possible
reasons:

1) the speedlight lose it's capacity just one stop.
2) the Sekonic meter measures the exposure one stop more than what a
meter that Metz used to test its GN reported.

which one is more reasonable?  thanks.

-
woody