Camera Flash Guide Number

The magnitude of guide numbers is a function of the following four variables. So shooting at f4 you could use the following equation to figure out that the sb 910 has a range of 8 5 meters. Guide numbers are the standardized numerical way of determining the power of a flash with a higher guide number representing a more powerful flash.

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The solid angle subtended by the circular or rectangular profile beam as it leaves the flash head.

Camera flash guide number. The total luminous energy in lumen seconds emitted by the flash head. Just to drive the point home the gn for iso 200 film would be 160 since you gain a stop of light with the faster film so gn f16 x 10 feet or 160. The simple rule is. Before we dig into some examples it s important to note.

There are flashes available that have a gn of 220 or even higher for iso 100 film. High guide number flashes provide a greater reach or working distance for a flash. Built in flash units typically have a guide number of around 10 14m so are okay for subjects reasonably close to the camera but are not powerful enough to cover large groups of people or great distances. So comparing as f stops works too.

In regards to the zoom range one flash might have coverage from 24 200mm on a full frame camera while another would only cover 18 105mm on a aps c camera. Understanding guide numbers the guide number can help you calculate the range of a specific flash by dividing the guide number by the f stop you plan on using. Or gn f number x distance. Flash to subject distance guide number f stopfor example the nikon sb 910 used in the video has a guide number of 34 meters.

Usually they are limited in the control they offer and won t accept accessories. Guide number distance x fstop number for any proper direct flash exposure. Flash guide number distance aperture and iso. Therefore double gn is double distance or double fstop number which is 2 ev stops of exposure.

Ideally you d like to capture photos that look like 3 all. Flash guide number formula. This can vary depending on how the manufacturer conducted their test. Ordinary guide number calculators just do a simple division modes a and b above independently.

Generally flashes which have a higher guide number would yield the stronger flasher output. 118 36 m at iso 100 for the flash head zoomed to 35mm the gn of 118 is close enough to the nikon s that the explanation is the same for 35mm flash head zoom. If your flash specifies guide number for 105 mm zoom but you are using it at 24 mm zoom you absolutely need to know and use the 24 mm zoom guide number see your flash manual for its complete guide number chart. In order to understand how a flash guide number is calculated.

The iso sensitivity setting. A guide number is the product of multiplying the f stop of an exposure with a given distance at iso 100. 197 60 m at iso 100 for the flash head zoomed to 200mm guide number.