02 gn review
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Speedlight Basics:
Michael E. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
Guide Numbers, Calibration and Application
1Sunday, November 13, 2011
Speedlight Basics:
Shutter speed has no effect on flash exposure.
Michael E. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
2Sunday, November 13, 2011
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. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
3Sunday, November 13, 2011
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. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
4Sunday, November 13, 2011
Speedlight Basics:
This leads us to the first fundamental truth about flash exposure...
Michael E. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
5Sunday, November 13, 2011
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. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
6Sunday, November 13, 2011
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.
Speedlight Basics:
Michael E. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
7Sunday, November 13, 2011
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. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
8Sunday, November 13, 2011
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. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
9Sunday, November 13, 2011
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. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
10Sunday, November 13, 2011
Speedlight Basics:
GN = Aperture x Flash to Subject Distance
Aperture = GN/Flash to Subject Distance
Flash to Subject Distance = GN/Aperture
Michael E. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
11Sunday, November 13, 2011
Speedlight Basics:
Michael E. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
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)
12Sunday, November 13, 2011
Speedlight Basics:
Michael E. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
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’)
13Sunday, November 13, 2011
Speedlight Basics:
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. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
The Set Up
14Sunday, November 13, 2011
Speedlight Basics:
Michael E. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
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)
The Set Up
15Sunday, November 13, 2011
Speedlight Basics:
Michael E. SternPhotographer Educator Radio Host Author
818-422-0696
Build A Better Photograph Dot Com
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.
The Set Up
16Sunday, November 13, 2011
Speedlight Basics:
Equivalent Exposures
Guide Number: 110
22 f/5
20 f/5.6
18 f/6.4
16 f/7.1
14 f/8
12.5 f/9
11 f/10
10 f/11
9 f/12.5
8 f/14
7.1 f/16
6.4 f/18
5.6 f/20
5 f/22
FSD Aperture22’ x f/5 = 110
7.1’ x f/16 = 113
14’ x f/8 = 112
17Sunday, November 13, 2011
Speedlight Basics:
Equivalent Exposures
Guide Number: 110
22 f/5
20 f/5.6
18 f/6.4
16 f/7.1
14 f/8
12.5 f/9
11 f/10
10 f/11
9 f/12.5
8 f/14
7.1 f/16
6.4 f/18
5.6 f/20
5 f/22
FSD Aperture
Notice the relationship between the FSD and aperture to maintain equivalent exposures.
18Sunday, November 13, 2011
22 f/5
20 f/5.6
18 f/6.4
16 f/7.1
14 f/8
12.5 f/9
11 f/10
10 f/11
9 f/12.5
8 f/14
7.1 f/16
6.4 f/18
5.6 f/20
5 f/22
Speedlight Basics:
Equivalent Exposures
Guide Number: 110
FSD Aperture
Notice the relationship between the FSD and aperture to maintain equivalent exposures.
19Sunday, November 13, 2011
22 f/5
20 f/5.6
18 f/6.4
16 f/7.1
14 f/8
12.5 f/9
11 f/10
10 f/11
9 f/12.5
8 f/14
7.1 f/16
6.4 f/18
5.6 f/20
5 f/22
Speedlight Basics:
Equivalent Exposures
Guide Number: 110
FSD Aperture
Notice the relationship between the FSD and aperture to maintain equivalent exposures.
20Sunday, November 13, 2011
22 f/5
20 f/5.6
18 f/6.4
16 f/7.1
14 f/8
12.5 f/9
11 f/10
10 f/11
9 f/12.5
8 f/14
7.1 f/16
6.4 f/18
5.6 f/20
5 f/22
Speedlight Basics:
Equivalent Exposures
Guide Number: 110
FSD Aperture
Notice the relationship between the FSD and aperture to maintain equivalent exposures.
21Sunday, November 13, 2011
100 110
125 125
160 140
200 160
250 180
320 200
400 220
500 250
640 290
800 320
1000 360
1250 400
1600 450
2000 500
Speedlight Basics:
Equivalent Exposures
Guide Number: 110
ISO GN
Notice the relationship between the ISO and GN to maintain equivalent exposures.
22Sunday, November 13, 2011
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.
23Sunday, November 13, 2011
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)
24Sunday, November 13, 2011
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