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A review of Guide Numbers.

A review of Guide Numbers.

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02 gn review 02 gn review Presentation Transcript

  • Speedlight Basics: Guide Numbers, Calibration and Application Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 1
  • Speedlight Basics: Shutter speed has no effect on flash exposure. Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 2
  • Speedlight Basics: Aperture does affect flash exposure. All things being equal, the larger the lens opening, a greater amount of light reaches the chip. Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 3
  • Speedlight Basics: Flash to subject distance does affect flash exposure. All things being equal, the closer the flash is to the subject, the greater the amount of light that falls on the subject. If more light falls on the subject, then more light will be reflected through the lens and onto the chip. Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 4
  • Speedlight Basics: This leads us to the first fundamental truth about flash exposure... Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 5
  • Speedlight Basics: Equivalent flash exposures are made by adjusting flash to subject distance and aperture. 1) When you move the flash closer to the subject (increasing the amount of light falling on the subject), you must compensate by closing down the aperture. Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 6
  • Speedlight Basics: Equivalent flash exposures are made by adjusting flash to subject distance and aperture. 2) When you move the flash further from the subject (decreasing the amount of light falling on the subject), you must compensate by opening up the aperture. Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 7
  • Speedlight Basics: Apertures and flash to subject distance changes behave predictably. Therefore, informed photographers can quickly calculate how to achieve a desired flash exposure. Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 8
  • Speedlight Basics: 1) Assume the output from a strobe is constant. If the lens is opened up one stop, the flash to subject distance must increase until one stop less light falls on the subject if you want to maintain an equivalent flash exposure. We can predict how far to move the flash to achieve a one stop change. Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 9
  • Speedlight Basics: Now that we can mathematically describe two of the three variables - flash power (GN) and aperture that control flash exposure, a simple equation allows us to solve for the third variable, the flash to subject distance. Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 10
  • Speedlight Basics: GN = Aperture x Flash to Subject Distance Aperture = GN/Flash to Subject Distance Flash to Subject Distance = GN/Aperture Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 11
  • Speedlight Basics: Assume your flash has a GN of 100 and you want to shoot at f/8. What FSD will provide normal exposure? FSD = GN/Aperture 12.5’ = 100/(f/8) Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 12
  • Speedlight Basics: Assume your flash has a GN of 100. Now you want to place your flash 8’ from the subject. What aperture will provide normal exposure? Aperture = GN/FSD f/12.5 = 100/(8’) Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 13
  • Speedlight Basics: The Set Up Guide numbers are affected by FSD changes. When the flash is moved closer the GN increases (the flash becomes more powerful) and when the flash is moved further away the GN decreases. (the flash becomes less powerful) Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 14
  • Speedlight Basics: The Set Up Guide numbers are affected by ISO changes. When the ISO increases the GN increases (the flash becomes more powerful) and when the ISO decreases the GN decreases. (the flash becomes less powerful) Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 15
  • Speedlight Basics: The Set Up Guide number changes track the aperture scale. Memorize the aperture scale and think of f/stops as feet and you’ll become a genius at working with your flash in manual mode and understand how it’s range is limited in iTTL mode. Michael E. Stern Photographer Educator Radio Host Author 818-422-0696 Build A Better Photograph Dot ComSunday, November 13, 2011 16
  • Speedlight Basics: FSD Aperture 22 f/5 22’ x f/5 = 110 20 f/5.6 18 f/6.4 16 f/7.1 14 f/8 14’ x f/8 = 112 Equivalent Exposures 12.5 f/9 11 f/10 Guide Number: 110 10 f/11 9 f/12.5 8 f/14 7.1 f/16 7.1’ x f/16 = 113 6.4 f/18 5.6 f/20 5 f/22Sunday, November 13, 2011 17
  • Speedlight Basics: FSD Aperture 22 f/5 20 f/5.6 18 f/6.4 16 f/7.1 14 f/8 Notice the relationship Equivalent Exposures 12.5 f/9 between the FSD and 11 f/10 aperture to maintain Guide Number: 110 10 f/11 equivalent exposures. 9 f/12.5 8 f/14 7.1 f/16 6.4 f/18 5.6 f/20 5 f/22Sunday, November 13, 2011 18
  • Speedlight Basics: FSD Aperture 22 f/5 20 f/5.6 18 f/6.4 16 f/7.1 14 f/8 Notice the relationship Equivalent Exposures 12.5 f/9 between the FSD and 11 f/10 aperture to maintain Guide Number: 110 10 f/11 equivalent exposures. 9 f/12.5 8 f/14 7.1 f/16 6.4 f/18 5.6 f/20 5 f/22Sunday, November 13, 2011 19
  • Speedlight Basics: FSD Aperture 22 f/5 20 f/5.6 18 f/6.4 16 f/7.1 14 f/8 Notice the relationship Equivalent Exposures 12.5 f/9 between the FSD and 11 f/10 aperture to maintain Guide Number: 110 10 f/11 equivalent exposures. 9 f/12.5 8 f/14 7.1 f/16 6.4 f/18 5.6 f/20 5 f/22Sunday, November 13, 2011 20
  • Speedlight Basics: FSD Aperture 22 f/5 20 f/5.6 18 f/6.4 16 f/7.1 14 f/8 Notice the relationship Equivalent Exposures 12.5 f/9 between the FSD and 11 f/10 aperture to maintain Guide Number: 110 10 f/11 equivalent exposures. 9 f/12.5 8 f/14 7.1 f/16 6.4 f/18 5.6 f/20 5 f/22Sunday, November 13, 2011 21
  • Speedlight Basics: ISO GN 100 110 125 125 160 140 200 160 250 180 Notice the relationship Equivalent Exposures 320 200 between the ISO and GN 400 220 to maintain equivalent Guide Number: 110 500 250 exposures. 640 290 800 320 1000 360 1250 400 1600 450 2000 500Sunday, November 13, 2011 22
  • Speedlight Basics: The ISO Scale 3 4 5 6 8 10 12 16 20 25 32 40 50 64 80 100 125 160 200 250 320 400 500 640 800 1000 1250 1600 2000 2500 3200 4000 5000 ISO changes have a profound affect on guide numbers.Sunday, November 13, 2011 23
  • Speedlight Basics: The Aperture Scale 1.0 1.1 1.3 1.4 1.6 1.8 2.0 2.2 2.5 2.8 3.2 3.6 4.0 4.5 5.0 5.6 6.4 7.1 8.0 9.0 10 11 12.5 14 16 18 20 22 25 29 32 36 40 45 50 56 64 72 80 90 Think of this as a ruler. (in feet)Sunday, November 13, 2011 24