Join Brent Winebrenner for an in-depth discussion in this video Finding the guide number of a strobe, part of Lighting for Photographers: Flash Exposure Fundamentals.
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In this movie we're going to begin the hands-on process of exploring how to really master your flash.…To do that, we'll start by explaining how you can find your flash's guide number and what…to do with it once you have it.…Small strobe manufacturers use the term guide number to rate the power of their pocket strobes.…A guide number is a numerical expression of the ability of the flash to create…at a normal exposure at any given ISO.…When you leaf through your manual, you should find the table that looks something like this.…
Because a higher guide number means more power and more power means a higher value, manufacturers…tend to inflate their published guide numbers.…This means that if you're serious about getting consistently good manual flash exposures,…you should perform your own guide number test.…Another reason to perform your own guide number test is because a guide number is dependent…upon the accuracy of the ISO rating of the camera sensor.…Same flash unit when placed on two different cameras will have two different effective…
Even with today's automatic flash systems, there are good reasons to understand how flash exposure really works. Brent details these concepts in this course. The course describes how to calculate the true power of your flash and how to modify its output to match your needs, a technique that can extend battery life, reduce recycle time, and provide exposure control that is more predictable than fully automatic modes. The course concludes with several shooting scenarios during which Brent explores the creative use of gels, reflectors, and other light modifiers.
- Understanding exposure basics
- Reviewing aperture, ISO, and shutter speed
- Adjusting strobe power and flash to subject distance
- Finding the guide number of a strobe
- Making calculations based on ISO
- Understanding power ratios