Lenses

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Lenses
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Lenses

• Lenses define 2 important things
• Angle of view (focal length)
• Aperture

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Angle of view
Camera sees a cone of vision, measured by the
angle of the cone
Narrow angles of view see very little, but the
subject is big
Wide angles of view see a lot, but the subject is
small
Wide angle
Narrow angle
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Focusing A look at the overall camera system
Film/Sensor Where the light is recorded
Lens Bends the light
Subject Source of light
Trajectory of light
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Result
Light converges at sensor
Light converges past sensor
Light converges before sensor
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Translating focal length into angle of view
For 35mm film sensor (diagonal 43mm)
For 1.5x APS-C sensor (diagonal 29mm)
Focal length Angle of view (degrees)
12mm 121.97
16mm 107.03
24mm 84.06
28mm 75.38
35mm 63.44
50mm 46.79
85mm 28.56
135mm 18.21
200mm 12.35
300mm 8.25
400mm 6.19
600mm 4.13
Focal length Angle of view (degrees)
12mm 100.48
16mm 84.06
24mm 62.01
28mm 54.50
35mm 44.79
50mm 32.18
85mm 19.26
135mm 12.20
200mm 8.25
300mm 5.50
400mm 4.13
600mm 2.75
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Translating focal length into angle of view
Lenses are always specified by focal
length Photographers are concerned with angle of
view (Depends on focal length and sensor
size) Is 90mm a narrow angle lens, or a
wide-angle lens? Problem We want to talk
in angles of view, but are given focal
lengths Solution We convert focal lengths to
35mm equivalent
Focal length Angle of view - APS-C sensor Angle of view - 5x4 Large format
90mm 18.21 84.20
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Translating focal length into angle of view
Angle of view Focal length - 35mm Focal length - 1.5x APS-C Focal length - 1.6x APS-C
121.97 12mm 8mm 7.5mm
107.03 16mm 11mm 10mm
84.06 24mm 16mm 15mm
75.38 28mm 19mm 18mm
63.44 35mm 23mm 22mm
46.79 50mm 33mm 32mm
28.56 85mm 57mm 53mm
18.21 135mm 90mm 84mm
12.35 200mm 133mm 125mm
8.25 300mm 200mm 188mm
6.19 400mm 266mm 250mm
4.13 600mm 400mm 375mm
Actual focal length
35mm equivalent focal length
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Translating focal length into angle of view
Angle of view Focal length - 35mm Focal length - 1.5x APS-C
110.53 15mm 10mm
77.41 27mm 18mm
54.50 42mm 28mm
32.18 75mm 50mm
19.26 128mm 85mm
12.20 203mm 135mm
8.25 300mm 200mm
5.50 450mm 300mm
4.13 600mm 400mm
Actual focal length
35mm equivalent focal length
To get the 35mm equivalent focal length,
multiply your actual focal length by the cameras
crop factor When we talk about focal lengths,
well assume they are 35mm equivalent
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Focal length ranges
Two types of lenses Zooms (variable focal
length) and Primes (fixed focal
length) Different focal lengths are useful for
different things

• Standard range
• Covers most commonly used focal lengths,
  28mm/wider, 70mm/longer
• General purpose photography
• Standard 18-55 kit lens is a standard range
  zoom

38mm
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Focal length ranges
Two types of lenses Zooms (variable focal
length) and Primes (fixed focal
length) Different focal lengths are useful for
different things

• Telephoto
• Gives a very narrow angle, 70mm and beyond
• Large magnification for faraway subjects
• Commonly used for sports, wildlife

320mm
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Focal length ranges
Two types of lenses Zooms (variable focal
length) and Primes (fixed focal
length) Different focal lengths are useful for
different things

• Ultrawide
• Gives a very wide angle, 24mm or wider
• Can cover extremely large objects in confined
  spaces
• Commonly used for landscapes, architecture,
  journalism

19mm
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Tools for the job
What focal length would you use for a huge
building? What focal length for shooting sports
from the sidelines? Covering a protest? Taking
a portrait?
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Tools for the job
What focal length would you use for a huge
building? What focal length for shooting sports
from the sidelines? Covering a protest? Taking
a portrait?
310mm
70mm
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Tools for the job
24mm
39mm
Angle of view goes hand-in-hand with subject
distance Subject distance defines
perspective. Perspective affects -Distortion -Co
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