Information on apertures, ƒ/stops and depth-of-field as related to digital photography and dSLRs.

1. Focal Length
ƒ/stops
Depth-of-Field
Selective Focus

2. Traditional LensTraditional Lens
Distance Scale
Depth-of-field Scale
ƒ/stops

3. Cutaway of LensCutaway of Lens
Lens clipped at
mounting site
Why there is not a ƒ/1

4. Aperture Basics
 Located in back of lens (called an iris diaphragm)
 Opening which light passes through into camera
 Variable size
 Written as fraction (ƒ/16)

5. Focal LengthFocal Length
Distance in mm
A “normal” lens for 35mm is 50mm long
The focal length is the distance from the secondary principal
point to the rear focal point of a lens.

6. Focal
Length

7. Focal LengthFocal Length
Wide Angle Lenses
 Ultra Wide
15mm to 20 mm
 Normal Wide
24mm to 40mm
24mm

8. Focal LengthFocal Length
50mm
Normal Lenses
 45mm to 55mm

9. Focal LengthFocal Length
85mm
Short Telephoto
 70 mm to 135mm
 85mm to 120mm
good for portraits

10. Focal LengthFocal Length
200mm
Long Telephoto
 150 mm to 300mm
Ultra Long Telephoto
 300 mm to 1000mm

11. 24mm24mm

12. 50mm50mm

13. 85mm85mm

14. 200mm200mm

15. Aperture TermsAperture Terms
 ƒ/stop
 ƒ/number
 focal ratio
 f-ratio
 relative aperture

16. Lenses Showing AperturesLenses Showing Apertures
1. Wide open, small ƒ/number
2. Closed down, large ƒ/number
 Remember ƒ/numbers or
ƒ/stops are fractions.

17. ƒ/Number Formulaƒ/Number Formula
 The f-number N is given
by formula to right
 ƒ is the focal length,
 D is the diameter of the
entrance pupil (effective
aperture).

18. F-number
 The standard f-stop scale where √2(square root
of 2) corresponds to the sequence of the powers
of : f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16,
f/22, f/32, f/45, f/64, f/90, f/128, etc.
 The values of the ratios are rounded off to these
to make them easy to remember and write
down.

19. Aperture & ƒAperture & ƒ/stops/stops
 Remember ƒ/stops are a fraction of the diameter of the lens.
 Larger numbers (ƒ/22)
 Smaller opening
 Less light
 Smaller numbers (ƒ/2)
 Bigger opening
 More light

20. What do the numbers really mean?
 When the lens is set to ƒ/2, the hole in the lens is 1/2 as big as the lens
is long.
 When the lens is set to ƒ/8, the hole in the lens is 1/8th as big as the
lens is long.
 Which hole is bigger, 1/2 or 1/8?
 Which hose would let more water through, one that's a half inch in
diameter or one that's one-eighth in diameter?
 Which ƒ/stop lets in more light, ƒ/2 or ƒ/8?
2 2.8 4 5.6
8 11 16 22
1.4

21. Standard ƒ/stops
ƒ/ 1.4, 2, 2.8, 4, 5.6, 8, 11,
16, 22, 32, 44, 64
Yellow numbers are
uncommon.

22. 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32
Know these numbers.
Small
amount of
light
Large
amount of
light -1 stop +1 stop

24. Controlling
Focus

25. Depth-of-Field — DoFDepth-of-Field — DoF

26. The distance in front of and beyond
the subject that appears to be in
focus.

27.  Light rays converge through a lens at different distances in front and
behind film plane in a cone.
 When a lens is in focus, light rays are sharp on the film plane.
 The circle of confusion is the “slice” of the cone at the film plane that is
not in focus.
 The farther the tip of the cone is from the film plane the larger the circle of
confusion.

29. Depth-of-field (DoF)
 Shallow DoF
 Only subject in focus
 ƒ/2, ƒ/2.8, ƒ/4
 Deep DoF
 Everything in focus
 ƒ/11, ƒ/16, ƒ/22
 Closer subjects (esp.
macro)
 Less DoF
 Shallow
 Distance subjects
 Greater DoF
 Deep

30. Shallow & Deep DoF
Shallow
Little in
focus
Deep
More in
focus
ƒ/5.6
@ 1,000
35 mm
ƒ/16
@ 125
35 mm

31. Depth-of-FieldDepth-of-Field
 Distance Scale

32. Depth-of-FieldDepth-of-Field
 Depth-of-field scale

33. Depth-of-FieldDepth-of-Field
 Use Depth-of-field scale in conjunction with distance
scale to tell depth-of-field.
 Red area is that in focus at given ƒ/stop.
 Here is the ƒ/2 reading, 4 feet is the only area in
focus.

34. Depth-of-FieldDepth-of-Field
 View from above.
 Red area is in focus at given ƒ/stop.
 Here is the ƒ/2 reading, 4 feet is the only area in focus.

35. Depth-of-FieldDepth-of-Field
 Side View
 Red area is in focus at given ƒ/stop.
 Here is the ƒ/2 reading, 4 feet is the only
area in focus.

36. Depth-of-FieldDepth-of-Field
 Red area is in focus at given ƒ/stop.
 At ƒ/8, area in focus is between 3.5
and 5 feet.

37. Depth-of-FieldDepth-of-Field
 View from above.
 Red area is in focus at given ƒ/stop.
 At ƒ/8, area in focus is between 3.5
and 5 feet.

38. Depth-of-FieldDepth-of-Field
 Side View
 Red area is in focus at given ƒ/stop.
 At ƒ/8, area in focus is between 3.5
and 5 feet.

39. Depth-of-FieldDepth-of-Field
 Red area is that in focus at given ƒ/stop.
 At ƒ/16, area in focus is between 3 and 7
feet.

40. Depth-of-FieldDepth-of-Field
 View from above.
 Red area is that in focus at given ƒ/stop.
 At ƒ/16, area in focus is between 3 and 7 feet.

41. Depth-of-FieldDepth-of-Field
 Side View
 Red area is in focus at given ƒ/stop.
 At ƒ/16, area in focus is between 3 and 7 feet.

42. Depth-of-FieldDepth-of-Field
 Red area is that in focus at given ƒ/stop.
 At ƒ/22, area in focus is between 2.5 and
14 feet.

43. Depth-of-FieldDepth-of-Field
 View from above.
 Red area is that in focus at given ƒ/stop.
 At ƒ/22, area in focus is between 2.5 and 14 feet.

44. Depth-of-FieldDepth-of-Field
 Side View
 Red area is in focus at given ƒ/stop.
 At ƒ/22, area in focus is between 2.5 and 14 feet.

45. Depth-of-Field & Point of FocusDepth-of-Field & Point of Focus
 The distance scale changes with the focus.
 Red line in the center is the point in focus.
 At ƒ/2, area in focus 3 feet.

46. Depth-of-Field & Point of FocusDepth-of-Field & Point of Focus
 The distance scale changes with the focus.
 Red line in the center is the point in focus.
 At ƒ/2, area in focus is just over 6 feet.

47. Depth-of-Field & Point of FocusDepth-of-Field & Point of Focus
 The distance scale changes with the focus.
 Red line in the center is the point in focus.
 The translucent red box is the area in focus.
 At ƒ/22, area in focus is from 3 feet to infinity.

48. Depth-of-Field & Point of FocusDepth-of-Field & Point of Focus
 Red, focus @ 4
feet.
 At ƒ/22, area in
focus is between
2.5 and 14 feet.
 Green, focus @ 6
feet.
 At ƒ/22, area in focus
is between 2.5 feet
and infinity.

49. Central Point of Interest & Selective FocusCentral Point of Interest & Selective Focus
Point
of
Focus

50. BlurredBlurred
BackgroundBackground
Eye goes to focused area

51. BlurredBlurred
BackgroundBackground
Eye goes to focused area

52. Blurred BackgroundBlurred Background
& Foreground& Foreground
Eye goes to
focused area

53. Selective Focus
Only Subject in Focus
•Foreground blurry
•Background blurry
ƒ/5.6
@ 500
400 mm

54. Selective Focus
Only Subject in Focus
•Background blurry
ƒ/8
@ 250
90 mm
Macro

55. Selective
Focus
Only Subject in
Focus
•Background blurry

56. ShallowShallow

57. ShallowShallow

58. ShallowShallow

59. ShallowShallow

60. ShallowShallow

61. Shallow — MacroShallow — Macro

62. Shallow — MacroShallow — Macro

63. Shallow — MacroShallow — Macro

64. Deep — MacroDeep — Macro

65. DeepDeep
Foreground
Mid ground
Background

66. DeepDeep

67. DeepDeep

68. DeepDeep

69. Deep DoF
ƒ/8
32 mm

70. Deep DoF
ƒ/9.9
24 mm

71. DeepDeep

72. DeepDeep

73. Think About
 Point of Focus (where camera focus is at)
 Exposure
Choose priority
○ Stopping action/showing motion (shutter speed)
○ DoF (ƒ/stop)
Shallow
Deep
Think how will…
○ Shutter speed effect DoF
○ DoF effect shutter speed
When you take a photo you should always
consider:

74. Think About
 Fast shutter speed means low ƒ/stops
 Slow shutter speeds means high ƒ/stops
 Remember: reciprocity (if you change ƒ/stop you must
change shutter speed)
Conversely
 High ƒ/stops (deep DoF) means slow shutter speeds
 Low ƒ/stops (shallow DoF) means fast shutter speeds
 Remember: reciprocity
In General:

75. Your Assignment: DirectionsDirections
 You are to take 8 sets of 2 photos (16 photos total)
demonstrating shallow and deep depth-of-field.
 Each set consists of:
 Identical photos with the same exact content and focus.
 Five similar items in a row.
 The only change should be the ƒ/stop with the exposure
adjusted (±0) so the exposure is reciprocal between the
two.
 One photo should be with an ƒ/stop less than ƒ/4 (or as low
as you can get i.e. ƒ/5.6).
 The other photo should be with an ƒ/stop greater than ƒ/11
(ƒ/16+ better).
 Remember to adjust shutter speed and/or ISO when
changing ƒ/stop. All photos should have reciprocal
exposures.

76. What to turn in
 Worksheet fully filled
out
 Contact sheet fully
labeled with
exposures
 One set of favorite
photos printed out
w/exposures
 Aperture & ƒ/stop
rubric

77. Your Assignment: Example
ƒ/4.3 @ 60 @ 400 ISO ƒ/16 @ 60 @ 1600 ISO

78. Your Assignment: Example
ƒ/4.3 @ 60 @ 400 ISO ƒ/16 @ 60 @ 1600 ISO

79. Your Assignment: Example
ƒ/4 @ 250 @ 400 ISO ƒ/22 @ 60 @ 3200 ISO

80. Your Assignment: Example
ƒ/4 @ 60 @ 400 ISO ƒ/11 @ 60 @ 3200 ISO

81. Your Assignment: Example 1
 This photo is ƒ/11 @ 60.
 What should the other photo be taken at?
Remember
Your are to take two
exposures
• One deep
• One shallow

82. Finding Reciprocal Exposure
Step 1
 First think about type of DoF (shallow or deep)
 Find the equivalent exposure for opposite DoF

83. Finding Reciprocal Exposure Step 2
 DoF is deep (ƒ/11)
 Choose new ƒ/stop (ƒ/2.8)
 ƒ/stop difference
 +4 stops
 Lets in more light
 Find new shutter speed
 DoF is deep (ƒ/11)
 Choose new ƒ/stop (ƒ/4)
 ƒ/stop difference
 +4 stops
 Lets in more light
 Find new shutter speed

84. Finding Reciprocal Exposure Step 3
 Find new shutter speed
-4 OR -3 stops
Lets in less light
 New reciprocal (equivalent) exposure
 ƒ/2.8 @ 1,000 or
 ƒ/4 @ 2.000

85. Your Assignment: Example 2
 This photo is ƒ/32 @ 60.
 What should the other photo be taken at?
Remember
Your are to take two exposures
• One deep
• One shallow

86. Finding Reciprocal Exposure Ans. #2
New exposure
ƒ/5.6
@ 2,000

87. Your Assignment: Example 3
 This photo is ƒ/4 @ 125.
 What should the other photo be taken at?
 Are there any limitations? How would you compensate?
Remember
Your are to take two
exposures
• One deep
• One shallow

88. Your Assignment: Example 3

89. Finding Reciprocal Exposure Ans. #3
New exposure ƒ/22 @ 4
But can only go to 60 so…
ƒ/16 @ 60
Not a shallow DoF
Will not work for assignment

90. Finding Reciprocal Exposure Ans. #3
New exposure ƒ/22 @ 4
But can only go to 60 so…
ƒ/16 @ 60
Not a shallow DoF
Will not work for assignment

91. Your Assignment: Example 4
 This photo is ƒ/8 @ 250.
 What should the other photo be taken at?
Remember
Your are to take two exposures
• One deep
• Ocne shallow

92. Finding Reciprocal Exposure Ans. #4
 Neutral DoF @ ƒ/8, need to make adjustment
 New exposure ƒ/16 @ 60 (deep)
 New exposure ƒ/2.8 @ 2,000 (shallow)

93. Your Assignment: Example 5
 This photo is ƒ/16 @ 125.
 What should the other photo be taken at?
Remember
Your are to take two exposures
• One deep
• Ocne shallow

94. Finding Reciprocal Exposure Ans. #5
New exposure ƒ/4 @ 2,000 (deep)