Join Ben Long for an in-depth discussion in this video Guide number considerations, part of Foundations of Photography: Flash.
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…All flash units are given a rating, called a guide number, that is…simply a number that is a guide to how powerful the flash is.…Now, as you might expect, a higher guide number indicates a flash with more power.…A flash with more power, though, is also going…to be physically larger than a flash with less power.…So if you want to keep the size and weight of your bag down then you…may not want to buy a flash with more power than you think you'll need.…Using the guide number, you can quickly get…a sense for what a flash can do lighting-wise.…
Guide numbers are specific to a particular focal length and aperture, and…your flash's manual should list the guide numbers for different focal lengths.…For example, according to the manual, this Canon 580EX has a guide number, or range,…of 190 feet when shooting with a 105 mm lens, at ISO 100.…All that data is in the manual,…you can get a PDF of the manual off of the…web, then check into this before you ever buy the flash.…You need to pay close attention to the…units that are specified with the guide number.…
Fortunately, it isn't difficult to get great results from flash, and in this course, photographer, author, and teacher Ben Long details the concepts and techniques behind effective lighting with flash. Ben starts with fundamentals that build on exposure principles taught in other installments of Foundations of Photography—simple techniques that improve the results from a camera's built-in flash. He then focuses on fill flash techniques and on using flash as a key light. The course also explores topics ranging from bouncing and syncing flash to shooting with one or more off-camera flash units.
- How flash works
- Balancing ambient light and flash
- Understanding flash ranges and modes
- When to use fill flash
- Using an external flash
- Bouncing flash to improve light
- Building up multiple flash images
- Purchasing a flash