Login or Join Now

Upload your photos, chat, win prizes and much more

Remember Me

Can't Access your Account?

New to ePHOTOzine? Join ePHOTOzine for free!

Guide number

Join Now

Join ePHOTOzine, the friendliest photography community.

Upload photos, chat with photographers, win prizes and much more for free!

Get the new ON1 Photo 10 and Save $100 Today. Use Code: GetPhoto10 View Offer
Indicates the output, or power, of an electronic flash. You can use the guide number to work out the aperture or flash to subject distance by dividing either into the guide number.

Related Terms