Digital Photography Getting Started

1
Digital Photography Getting Started

• Class 5
• Understanding Your Camera Lens
• John Byers
• jbyers2_at_mail.com
• Class website www.notlong.com/c4d-dp

2
Class topics

• Digital basics
• Controlling sharpness
• Getting exposure correct
• Using light and color creatively
• Understanding your camera lens
• Elements of composition and style
• Weekend photo assignments

3
This time

• The camera lens
• How a lens works
• How focal length affects pictures
• Assignment results
• Experiment with camera white balance settings
  lighting techniques
• Photo assignment

4
Photo essay Series of pictures on a single
subject
5
The camera lens

• How a lens works
• Lens focal length and angle of view
• Zoom lens
• Normal
• Wide-angle
• Telephoto
• Lens focal length and portraits
• Perspective how a photograph shows depth

6
A lens is not needed to take a photograph

• In a pinhole camera, light waves from the
  object converge on the pinhole and focus the
  image upside down on the film

Object Pinhole Film
First drawing of pinhole camera obscura by
astronomer Gemma Frisius, who used the technique
to study the solar eclipse of 1544
7
The camera lens design depends on the property of
light to bend

• Light is bent when it passes between substances
  having different densities

8
The camera lens bends light in a precise manner,
redirecting rays to converge at a point

• Light rays are bent so that subject in front of
  the lens is focused behind it focal plane

Focal plane
9
Focusing the lens involves changing its distance
from image sensor focal plane
10
Light rays from a closer point converge farther
away from the lens than light beams from a
distant point
1/s 1/i 1/fL 1/8 1/i 1/fL Lens focal
length is defined by the distance between lens
and focused image on sensor of a subject at
infinity. Focal length is often referred to as
angle of view by photographers.
Focal plane image
11
Focal length of lens describes its magnifying
power

• On digital cameras, focal length is often
  expressed as 35mm film camera equivalent
• Higher focal length number indicates a greater
  image magnification
• Telephoto 100-300mm
• Normal 50mm (human eye)
• Wide angle 18-35mm
• Typical point shoot camera 3x zoom range
  35-105mm (35mm equivalent)

12
A zoom lens allows choice of any focal length
within the lens design range

• Angle of view / magnification trade-off
• Zooming out uses shorter focal length,
  providing wide-angle view
• Zooming in uses longer focal length, narrowing
  field of view so objects appear larger

13
Zooming in magnifies by cropping the scene
tighter than a wide-angle lens
Collection of photos taken from same position
with lenses ranging from wide angle to telephoto
24mm, 35mm, 50mm, 100mm, 200mm, 300mm
14
Typical digital camera image sensors are smaller
in size than 35mm film frame

• Image sensor size as compared to 35mm film frame
  (24 x 36mm)

35mm film frame 1.5x DSLR sensor size, 4x - 6x
compact sensor size
15
Image sensor smaller size crops the scene,
providing focal length multiplier effect for
DSLR interchangeable lenses
35mm film
Digital SLR image sensor
50mm normal lens in typical DSLR camera
performs like a 80mm short-telephoto lens (28mm
wide-angle lens performs like a 45mm normal lens)
16
Lens optics

• A cross-section of a camera lens shows it is
  constructed of a complex series of multiple
  lenses
• The array of concave and convex lens elements is
  designed to correct for optical aberrations, but
  can also produce flares use lens shade to
  prevent

17
Choosing lens focal length telephoto

• Telephoto lens is called a long lens
  typically 100mm to 300mm and above (35mm film
  camera equivalent) 80mm is a short telephoto
• The longer the lens, the farther away the camera
  will be positioned from the subject to frame the
  picture
• Long lenses are useful for sporting events and
  wildlife photographing a boat under sail while
  standing on the shore might require a 300mm lens
• A 100mm lens works well for portraits a longer
  lens could do the job, but would require
  positioning the camera further away from the
  subject

18
Zooming in is great for portraits

• Zooming in allows filling the frame from a
  distance (use optical zoom not digital)
• Keeping at a distance allows candid shots and
  avoids an exaggerated perspective that can result
  from working close to the subject with a shorter
  focal length lens
• Short depth-of-field nicely blurs background

19
The problem with digital zoom
Optical zoom provides good results in this 5Mp
image
1.6x digital zoom applied to 5Mp image results in
cropped, low quality 2Mp upsampled image
20
Choosing lens focal length wide angle

• Wide angle lens is called a short lens
  typically 18mm to 35mm (35mm film camera
  equivalent)
• Shorter lens gives wider view very wide angle
  lens introduces distortion fish-eye lens
  (16mm or less) is the extreme
• Short lenses allow getting more in the picture
  while standing close to the subject  
• Useful for capturing surroundings, such as street
  scenes and landscapes, and indoors in confined
  spaces to include entire scene

21
Wide angle lens captures great scenics
22
Wide angle lens may introduce perspective
distortion
23
Wide-angle close-ups distort facial features,
giving a "fish bowl" effect

24
Perspective is provided at the expense of
distortion
25
Perspective is provided at the expense of
distortion
26
Effects of zooming

• Susceptibility to camera shake. Zooming in
  (telephoto) produces binocular effect,
  increasing sensitivity to camera movement.
• Lens speed. Zooming in slightly decreases largest
  lens aperture on most lens designs, effectively
  lowering lens speed (smaller maximum aperture,
  higher f/stop e.g., f/4.5 ? f/5.6 from wide
  angle to telephoto zoom)
• Depth of field. Zooming out (wide angle) provides
  greatest depth of field at a given subject
  distance. Zooming in, like moving closer,
  decreases depth of field.

27
Wide angle lens makes foreground objects appear
larger telephoto lens makes far away objects
appear closer
28
Changing focal length and camera-to-subject
distance alters perspective
Wide angle(taken at near distance)

• If camera is moved further away from the
  foreground subject and then zoomed in (right), it
  causes the background to appear much closer
  relative to the foreground

Telephoto(taken at far distance)
29
Telephoto shots can compress space
Wide-angle photo, taken with subjects at close
distance, shows expansive background
Telephoto shot of distant subjects shows only
portion of background, which appears closer
30
Telephoto shots can compress space
Wide-angle photo, taken with subjects at close
distance, shows expansive background
Telephoto shot of distant subjects shows only
portion of background, which appears closer
31
Landscape mode for distant shots

• Use for shots where background is important part
  of scene
• May require getting out of Automatic mode
• May disable flash, autofocus
• Typically forces higher aperture for large focus
  depth field, and autofocus bias toward distant
  focus point (or infinity)

32
Focus and depth-of-field sharpness

• Focus determines the plane of critical focus
  the distance at which objects in photo will be
  sharpest
• Depth of field (DOF) is the range of distance in
  the photo, between near and far, that appears to
  be in focus the range of perceived sharpness in
  front and behind the focused subject.
• DOF extends from about 1/3rd in front of the
  point of focus to 2/3rds behind it there is
  twice as much DOF behind the point of focus as in
  front of it
• DSLR cameras offer DOF preview button

33
Aperture and depth of field
Older lenses providedDOF scale
34
Subject distance, zoom and DOF
35
Good news / bad news compact cameras provide
large depth-of-field

• Nature of physically small image sensor size and
  short focal length lens found in compact cameras
  makes it difficult to attain shallow
  depth-of-field
• N x f-stop rule of thumb Digital camera DOF is
  same as 35mm (or full-frame digital) camera with
  f-stop setting of N x F
• N digital camera focal length multiplier
  ratio (function of image sensor size relative to
  35mm)
• F digital camera aperture f-stop setting

36
Sensor size, FLMR
37
Subject size, zoom and DOF
Telephoto, far distance
Wide angle, near distance
28mm, f/4
100mm, f/4
28mm, f/22
100mm, f/22
For constant subject size and given aperture, all
lenses give same depth of field
38
Maximum depth-of-field

• Important for photographs of landscapes and
  scenes where a distant horizon is a part of the
  picture

Near and far DOF limits can be calculated for
lens focal length, aperture and focus distance
39
Hyperfocal distance is nearest focus point for
DOF that extends to infinity

• For lens focused at hyperfocal distance
• Far limit of acceptable sharpness is at infinity
• Near limit is about half the hyperfocal distance
• Hyperfocal distance be calculated for given lens
  focal length and aperture
• Shorter for small apertures (high f-numbers) and
  for lenses with shorter focal lengths

40
Focusing tips

• The auto focus system adjusts the focus to make
  the subject in the center of the viewfinder
  appear critically sharp. (Some cameras use
  multi-point focusing.)
• Auto focus may have trouble focusing in certain
  situations
• Low contrast, such as when the subject is poorly
  illuminated
• When both near and distant objects fall within
  the focus point
• When the subject is moving
• If camera cant focus, may beep or blink a lamp
  may prevent taking picture
• Use focus lock technique to prefocus on
  high-contrast object at the same distance as
  subject
• Some cameras provide for adjustable manual focus

41
Next time Elements of composition style

• Composition rules of thumb
• Seeing creatively
• Experimenting trying new techniques
• Finding your distinctive, personal style
• Special purpose photos panorama, macro
• Assignment
• Experiment with different zoom settings
• Photo assignment

42
Photo assignment Images with color accent
43
Perspective correction using Photoshop
Before
After
44
Perspective correction technique

• Select area to transform
• CtrlA select all
• Image gt Transform
• Perspective apply one-point perspective
• Skew slant vertically horizontally
• Distort stretch in all directions
• Free Transform distort plus rotation

45
Perspective correction example