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

Film/Sensor Where the light is recorded Lens Bends the light Trajectory of light Subject Source of light Focusing A look at the overall camera system

Light converges at sensor Light converges past sensor Light converges before sensor Result: ‘In focus’‘Out of focus’

Result: ‘In focus’ Circle of confusion Image doesn’t have to perfectly converge. If it converges within a “circle of confusion”, it is still ‘in focus’ ‘In focus’ ‘Out of focus’

In focus Out of focus

Things at a certain distance are “in focus” (perfectly sharp) The further from this distance, the blurrier things are There is a range of distance where things are ‘sharp enough’ to be considered ‘in focus’. This range is known as the “depth of field” Amount of Blur Depth of field

Range that is ‘in focus’ Focus point Near limit of focus Far limit of focus Film/Sensor Where the light is recorded Circle of confusion Maximum non-convergance allowed to be ‘in focus’

Depth of field Circle of confusion When using a bigger lens (larger aperture), the depth of field shrinks

Depth of field Circle of confusion Longer subject distances mean larger depth of field range

Circle of confusion Longer focal lengths mean smaller depth of field range Depth of field

A = aperture f-number (e.g. f5.6) f = focal length (e.g. 50mm) d = distance to subject (e.g. 3000mm) c = circle of confusion (e.g..02mm) Factors to note: Smaller apertures (larger f-number) gives larger depth of field Shorter focal length gives larger depth of field Longer distance to subject gives larger depth of field Larger circle of confusion gives larger depth of field

As aperture increases, depth of field increases

As focal length increases, depth of field decreases. At very wide focal lengths (ultrawide), depth of field increases rapidly

Translating focal length into angle of view Angle of viewFocal length - 35mmFocal length - 1.5x APS-CFocal length – 1/1.7” 62.01°36mm24mm8mm Actual focal length35mm equivalent focal length

As subject distance increases, depth of field increases At very long subject distances, depth of field increases rapidly (hyperfocal distance)

For a constant magnification, depth of field is roughly the same across distance/focal length combinations

Landscape/scenery Bokeh 40mm, f/ mm, f/2.8

Uses of large depth of field Landscape/scenery Architecture Small depth of field Macro

Uses of small depth of fieldPortraitsFlowers Sports Isolation

Lenses Two types of lenses: Zooms (variable focal length) and Primes (fixed focal length) Large aperture zooms Up to f/2.8 aperture Expensive! Canon f2.8 $999 Canon f2.8 $1139

Focal length ranges Two types of lenses: Zooms (variable focal length) and Primes (fixed focal length) Large aperture primes Very large apertures (f/2, f/1.8, f/1.4, f/1.2) (Mostly) Cheaper than large aperture zooms Fixed focal length (angle of view) Nikon 85mm f1.8 $419 Canon 50mm f1.4 $316 Canon 50mm f1.8 $83