Lenses

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

Angle of viewCamera 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

Film/SensorWhere the light is recorded

LensBends the light

Trajectory of lightSubject

Source of light

FocusingA look at the overall camera system

Light converges at sensor

Light converges past sensor

Light converges before sensor

Result:

‘In focus’

‘Out of focus’

‘Out of focus’

Translating focal length into angle of view

)length focal*2

diagonalsensor 2arctan( of view Angle

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°

For 35mm film sensor (diagonal: ~43mm)

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°

For 1.5x APS-C sensor (diagonal: ~29mm)

Translating focal length into angle of view

Focal length Angle of view - APS-C sensor Angle of view - 5x4 Large format90mm 18.21° 84.20°

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 lengthsSolution: We convert focal lengths to “35mm equivalent”

Translating focal length into angle of view

Angle of view Focal length - 35mm Focal length - 1.5x APS-C Focal length - 1.6x APS-C121.97° 12mm 8mm 7.5mm107.03° 16mm 11mm 10mm

84.06° 24mm 16mm 15mm75.38° 28mm 19mm 18mm63.44° 35mm 23mm 22mm46.79° 50mm 33mm 32mm28.56° 85mm 57mm 53mm18.21° 135mm 90mm 84mm12.35° 200mm 133mm 125mm

8.25° 300mm 200mm 188mm6.19° 400mm 266mm 250mm4.13° 600mm 400mm 375mm

Actual focal length35mm equivalent focal length

Translating focal length into angle of view

Angle of view Focal length - 35mm Focal length - 1.5x APS-C110.53 15mm 10mm

77.41 27mm 18mm54.50 42mm 28mm32.18 75mm 50mm19.26 128mm 85mm12.20 203mm 135mm

8.25 300mm 200mm5.50 450mm 300mm4.13 600mm 400mm

Actual focal length35mm equivalent focal length

To get the “35mm equivalent” focal length, multiply your actual focal length by the camera’s crop factor

When we talk about focal lengths, we’ll assume they are “35mm equivalent”

Focal length rangesTwo types of lenses: Zooms (variable focal length) and Primes (fixed focal length)

Different focal lengths are useful for different things

Standard rangeStandard range• Covers most commonly used focal lengths, 28mm/wider, 70mm/longer• General purpose photography• Standard 18-55 “kit” lens is a standard range zoom 38mm38mm

Focal length rangesTwo types of lenses: Zooms (variable focal length) and Primes (fixed focal length)

Different focal lengths are useful for different things

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

320mm320mm

Focal length rangesTwo types of lenses: Zooms (variable focal length) and Primes (fixed focal length)

Different focal lengths are useful for different things

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

19mm19mm

Tools for the jobWhat focal length would you use for a huge building?

What focal length for shooting sports from the sidelines?

Covering a protest?

Taking a portrait?24mm110mm

Tools for the jobWhat focal length would you use for a huge building?

What focal length for shooting sports from the sidelines?

Covering a protest?

Taking a portrait?310mm70mm

24mm 39mm

70mm

Tools for the job

Angle of view goes hand-in-hand with subject distance

Subject distance defines perspective.

Perspective affects:-Distortion-Context