Number used to indicate the light output of a flash unit, affected by the type of reflector used
A number that relates the output of electronic flash when used with a particular speed film. The higher the guide number, the more the light output. Guide numbers, or GN serve as a way to calculate aperture when shooting flash in manual exposure mode. Dividing distance into guide number gives the aperture: For example, a flash with a guide number of 56 (with ISO 100 film) would give a correct exposure at 10 feet with an aperture of f/5.6. With the state of today's automatic exposure flashes, guide numbers today are mostly useful for comparing the relative power of one flash to another.
A numerical valuation for the power of a flash. Used to determine the aperture that will produce correct flash exposure with a given ISO and distance from flash to subject. Guide Number = f/stop x Distance.
A number used to describe the output capacity of a flash. Usually expressed using an ISO film speed of 100. Divided by the distance from flash to subject it yields aperture.
n. in flash photography. A number in meters or feet which relates to the power of the flash unit, usually at 100 ISO. The guide number divided by the subject distance gives the correct aperture for a manual exposure. Similarly, for an automatic flash the guide number divided by the aperture used gives the maximum subject distance. _______________________________________________________
Provides information about the amount of light of a flash unit (dependent on the corresponding focal length).
The number which indicates the effective power of a flash unit. For a given film speed, the guide number divided by the distance between the flash and the subject gives the appropriate f stop to use.
The Guide Number is another way of stating BCPS. The Guide number tells you what aperture setting you will need on the camera for a given light to subject distance at a given film speed. For example, if you are using an ISO 100 film, you would use the ISO 100 GN and divide this number by the distance from light to subject to find the correct lens aperture. If, for example, the ISO 100 GN for your flash were 110, and your subject were 10 feet from the flash, you would use an f11 aperture. By looking at an appropriate chart, you could also find that an ISO 100 GN of 110 is simply another way of stating a rating of 2800 BCPS. Like the BCPS rating, the Guide Number only has relevance when the flash is used direct.
an indication of the power of the flash
A reference number that allows you to do two things. First you can easily compare the relative strengths of different flash units. ( A higher guide number indicates more light uotput) Second, you can use it to assist in determining the correct aperture when using the flash unit. This is not terribly important due to the fact that most flash units are fully automatic. back to the
The output power rating of a electronic flash unit
A rating of a flashes power. Good to use when shopping for flash and comparing different models.
A number rating for a flash unit that can be used to calculate the correct exposure for a particular film speed and flash-to-subject distance.
a number that represents the strength of a strobe. The guide number is used in the guide number equation to allow the photographer to select a combination of aperture and distance that will result in a proper exposure.
A rating of a flash's power.
Most flashguns for a camera list a rating referred to as a Guide Number, or GN. This number is used for manual settings to determine the proper aperture based on the distance from the subject. Guide numbers are also rated assuming ISO 100 speed film. If your flash has a guide number of 120 and the subject is 12 feet away, chose the aperture closes to 10 (120/12=10), which would be f/11. If the subject was 20 ft away, the result would be close to 6 (120/20=6), or f/5.6. This is all under the assumption that 100 speed film is being used. If 400 speed film was being used, which is 2 stops faster film, meaning it requires less light to expose the film, the aperture would be stopped down 2 stops, from f/5.6 to f/11. Instead of 400, if 200 was being used, then the subject do camera distance would require f/8.
a number used to calculate the f-setting (aperture) that correctly exposes a film of a given sensitivity (film speed) when the film is used with a specific flash unit at various distances from flash to subject. To find the f-setting, divide the guide number by the distance
term sometimes used to describe a flash factor, which provides a guide to correct exposure when using flash.
The guide number for an electronic camera flash measures its ability to illuminate the subject.