[馬仔]

光量的單位問題
我想問(火數)Ws點樣轉做NG值
例:150ws=幾多NG呢?
請指明路
謝謝

[swhsimon]

1. 火數--- is "Watt" , It is a Unit of Power .
means Engery used per Second

NG --No such a term !


2. if GN-- means "Guide Number" used in Flash light.

GN bigger, the Flash Light ability Bigger.

It is definded as :
GN = Meter x f (under ISO100 )

It is is conventient for Flash Ligh user to calculate which " f " value is used when how meter is far from you .

example:
GN =42
f = 42 / distance in meter

If an object is 8 meter from you, then you should use f=8
If an object is 10 meter from you, then you should use f=4.2

3. Anyway,
Guide Number, GN has NO direct Relation with Power of a Flash light.
It just has indirect relation.
Since GN value will depend on so many condition, e.g Electronic design of the Flash, Componets.....so ..many thing ..la....la..
Of course, bigger power may have more chance to be bigger GN .

SO , NO Formula !

[swhsimon]

Sorry....Typing Mistake:

example:
GN =42
f = 42 / distance in meter

e.g 42 / 4 = 8
If an object is 4 meter from you, then you should use f=8


If an object is 10 meter from you, then you should use f=4.2
e.g 42 / 10 = 4.2

[swhsimon]

In my experience

1. The price of Flash is always base on this

GN >= 40 , a rank of price
GN 30 to 40, a rank of price
GN 20 to 30 , a rank of price

If GN less than 20 , it just a "Toy " grade level.

2. Sorry, I forget GN Value should be under following condition :
a. Standard Lense
b. ISO 100
c. GN in meter.

3. So, compare the ability should be base on the same condition.
If not, GN value is hard to compare the ability of Flash.