Join Brent Winebrenner for an in-depth discussion in this video Analyzing the results of the guide number test, part of Lighting for Photographers: Flash Exposure.
So we just finished shooting our guide number test.…I took a series of portraits of Gabby bracketing the aperture, and now we're going to see how…to use those images to establish what are guide number is.…So let's get straight into that.…So here are the images that we just took for the guide number test, and you can see that the bracketing worked.…We went from f/22 all the way down to 5.6.…Clearly, the first five or six of these are underexposed, and the last three or four are overexposed.…So just by eyeballing it, I can tell.…
I'm going to open up this image, the one taken at f/11.…I'm going to open up the one at 10, at 9, and at f/8.…So let's just take a look at these guys, and we're going to do that in the Raw processor.…So what I'm looking for is to see which exposure holds detail in the white shirt and gives…me values of roughly 245 in the brightest spot, because then I can work with that exposure…to really give me a good tight exposure.…
Here you can see I'll be looking at the RGB values up here.…
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