Guide Number

[ang]

I'm trying to decide on a flash for my camera nikon n65. This will be my first flash.

I'm wondering what importance the different guide numbers are? In the specs of each flash, it seems some guide numbers change depending on the focal length? I understand the larger the guide number, the larger the distance the flash will shoot. Is that all?

 

[ksmattfish]

Guide Number divided by distance to subject equals the aperture for correct exposure.

Example: GN 110 (ISO 100/feet) divided by 10 feet = f/11 (for ISO 100)

 

[Daniel]

Guide Number divided by distance to subject equals the aperture for correct exposure.

Example: GN 110 (ISO 100/feet) divided by 10 feet = f/11 (for ISO 100)

That belongs in the sticky at the top

 

[ang]

So what min. guide number should I look for in a flash if I want to do some portraits with bounce flash?

 

[ksmattfish]

Shrug? That depends on your film speed, distance to subject ( for bounce estimate total distance of the bounce, and then open up the aperture at least one stop depending on what you are bouncing it off of).

I like to go with the most powerful I can afford. You can always cut down power, but you can't make the flash more powerful. I like GN 120.