What is a good flash guide number?
It is easy to use guide numbers to calculate either an aperture or a flash-to-subject distance. Consider a flash device with a rating of 28 meters (which might be marked “92 feet”, “28 DIN”, “28/92”, “92”, etc.).
How do I find my flash guide number?
For any given “correct flash exposure” situation, guide number is simply numerically equal to the aperture number (like the number 8 in f/8) multiplied by the subject distance (like 10 feet). Then for example, the guide number is f/8 x 10 feet = GN 80 (feet units).
What do the numbers on a strobe light mean?
The flash guide number (GN) is a measure of the distance at which the flash can illuminate a subject. The higher the guide number, the greater the distance at which the light from the flash is sufficient for optimal exposure.
How does flash compare guide numbers?
The simple rule is: Guide Number = distance x fstop Number (for any proper direct flash exposure). Therefore, double GN is double distance or double fstop Number (which is 2 EV stops of exposure). So comparing as f/stops works too.
Is a higher guide number better?
Use guide numbers to get a general sense of the power of an electronic flash, but if you’re trying to compare two virtually identical units, don’t get too hung up on one with a slightly higher guide number.
How do guide numbers work?
Guide numbers are based on a simple mathematical equation that states: the light output of an electronic flash is equal to the distance of the flash unit from the subject multiplied by the lens aperture, or f/stop.
What would be the F stop with a guide number of 80 and a distance of 10 feet?
f/8
Flash Guide Number Formula
| Guide Number | F-Stop | Calculation |
|---|---|---|
| 40 | f/4 | GN = 10 ft. x f/4 = 40 |
| 80 | f/8 | GN = 10 ft. x f/8 = 80 |
| 110 | f/11 | GN = 10 ft. x f/11 = 110 |
| 160 | f/16 | GN = 10 ft. x f/16 = 160 |
How does guide number work?
How is guide number defined?
[′gīd ‚nəm·bər] (graphic arts) A number that relates the output of a light source (such as a flashbulb) to the sensitivity of a particular film; when the number is divided by the distance in feet to the subject, it gives the T stop at which the lens should be set.
Does ISO matter with flash?
While you’re shooting with flash, a good principle to remember when selecting your ISO value is to determine how you want your entire scene to look. Start by focusing on the background first. Dial in your ISO value so that your camera produces an image with the background you desire.