Apple Aperture Digital Photography Fundamentals User Manual
Aperture
Digital Photography
Fundamentals
K
Apple Computer, Inc.
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registered in the U.S. and other countries.
Aperture is a trademark of Apple Computer, Inc.
1
Contents
Preface 5 An Introduction to Digital Photography Fundamentals
Chapter 1 7 How Digital Cameras Capture Images
7
Types of Digital Cameras
8
Digital Single-Lens Reflex (DSLR)
9
Digital Rangefinder
11
Camera Components and Concepts
11
12
14
14
15
16
17
17
20
20
21
21
21
22
22
22
22
23
25
Lens
Understanding Lens Multiplication with DSLRs
Understanding Digital Zoom
Aperture
Understanding Lens Speed
Shutter
Using Reciprocity to Compose Your Image
Digital Image Sensor
Memory Card
External Flash
Understanding RAW, JPEG, and TIFF
RAW
Why Shoot RAW Files?
JPEG
TIFF
Shooting Tips
Reducing Camera Shake
Minimizing Red-Eye in Your Photos
Reducing Digital Noise
Chapter 2 27 How Digital Images Are Displayed
27
The Human Eye’s Subjective View of Color
29
Understanding How the Eye Sees Light and Color
30
Sources of Light
30
31
The Color Temperature of Light
How White Balance Establishes Color Temperature
3
31
32
33
33
34
34
35
35
36
36
Measuring the Intensity of Light
Bracketing the Exposure of an Image
Understanding How a Digital Image Is Displayed
Additive vs. Subtractive Color
Understanding Color Gamut
Displaying Images Onscreen
The Importance of Color Calibrating Your Display
Apple Cinema Displays Are Proof Perfect
Displaying Images in Print
Printer Types
Chapter 3 37 Understanding Resolution
37
Demystifying Resolution
37
38
40
41
41
42
42
42
43
43
44
45
Learning About Pixels
Learning About Bit Depth
How Resolution Measurement Changes from Device to Device
Mapping Resolution from Camera to Printer
Camera Resolution
Display Resolution
About the Differences Between CRT and Flat-Panel Display Resolutions
Printer Resolution
Calculating Color and Understanding Floating Point
Learning About Bit Depth and Quantization
Learning About the Relationship Between Floating Point and Bit Depth
Understanding How Aperture Uses Floating Point
Appendix 47 Credits
4
Contents
An Introduction to Digital Photography Fundamentals
This document explains digital terminology for the
professional photographer who is new to computers
and digital photography.
Aperture is a powerful digital photography application designed to help you produce the
best images possible. However, many factors outside of Aperture can affect the quality of
your images. Being mindful of all these factors can help prevent undesirable results.
The following chapters explain how your camera captures a digital image, how images
are displayed onscreen and in print, and how cameras, displays, and printers measure
image resolution.
Preface
5
1
How Digital Cameras Capture Images
1
If you’ve previously shot film and are new to digital media,
this chapter is for you. Here you’ll find basic information
about the types of digital cameras, camera components
and concepts, and shooting tips.
People take photographs for many different reasons. Some take pictures for scientific
purposes, some shoot to document the world for the media, some make their living
shooting products for advertisements, and others shoot for enjoyment or purely artistic
purposes. Whatever your reason for picking up a camera and framing an image, an
understanding of how cameras work can help you improve the quality of your images.
This chapter covers:
Â
Types of Digital Cameras (p. 7)
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Camera Components and Concepts (p. 11)
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Understanding RAW, JPEG, and TIFF (p. 21)
Â
Shooting Tips (p. 22)
Types of Digital Cameras
In its most basic form, a digital camera is a photographic device consisting of a
lightproof box with a lens at one end, and a digital image sensor at the other in place
of the traditional film plane. Advances in digital photography are fast providing a wide
spectrum of features and options that can be challenging for the new digital
photographer to master.
There are two basic types of digital cameras: digital single-lens reflex (DSLR) and
digital rangefinder.
7
Digital Single-Lens Reflex (DSLR)
This camera is named for the reflexing mirror that allows you to frame the image
through the lens prior to capturing the image. As light passes through the DSLR
camera’s lens, it falls onto a reflexing mirror and then passes through a prism to the
viewfinder. The viewfinder image corresponds to the actual image area. When the
picture is taken, the mirror reflexes, or moves up and out of the way, allowing the open
shutter to expose the digital image sensor, which captures the image. Most features on
a DSLR are adjustable, allowing for greater control over the captured image. Most DSLR
cameras also allow the use of interchangeable lenses, meaning you can swap lenses of
different focal lengths on the same camera body.
Viewfinder
(shows the actual
image frame)
Reflexing mirror
(swung open)
Prism
Digital image sensor
Mirror
Lens
Processor
8 Chapter 1
How Digital Cameras Capture Images
Digital Rangefinder
There are two classes of digital rangefinder cameras: coincident rangefinder and
point-and-shoot.
Coincident Rangefinder
Unlike DLSR cameras, the coincident rangefinder does not provide the photographer
with the ability to view the subject through the lens. Instead, the coincident
rangefinder employs a mirror or prism that uses triangulation to unite the images seen
through the viewfinder and a secondary window to bring the subject into focus. The
photographer sees two images overlaid on top of one another in the viewfinder, and
the image is not in focus until there is a single image. As with DSLRs, most features in a
coincident rangefinder are adjustable, allowing for maximum control over the captured
image. An advantage to using a coincident rangefinder over a DSLR is that the lack of a
reflexing mirror significantly reduces camera shake. Camera shake is due to hand
movement or the vibration of the reflexing mirror found in a DSLR, and can cause
blurring of the image.
Viewfinder
Semitransparent
mirror
Image sensor
Out of focus
(image overlays not aligned)
Beamsplitter
semitransparent mirror
Light-gathering window
Reflective
Rotating mirror/prism
Light source
light
In focus
(image overlays aligned)
Chapter 1
How Digital Cameras Capture Images
9
Digital Point-and-Shoot
This is a lightweight digital camera, aptly named after the two steps required of the
photographer to capture an image. Basically, point-and-shoot cameras require pointing
the camera and taking the picture without manually adjusting settings such as the
aperture, shutter speed, focus, and other settings that professional photographers
routinely set on more sophisticated cameras. Of course, some point-and-shoot digital
cameras do include adjustable aperture and shutter settings. Point-and-shoot digital
cameras are generally light and small, have built-in automatic flash, require no
adjusting of focus, and most often include an LCD display that allows you to view the
image through the lens in real time via the digital image sensor. Most manufacturers of
point-and-shoot cameras separate the viewfinder from the lens assembly to simplify
construction and achieve a compact size. The lens, aperture, and shutter are one
assembly, irremovable from the camera itself.
LCD display
Viewfinder
(shows an approximation
of the image frame)
Light source
Reflective
light
LensDigital image sensor
Because rangefinder cameras separate the optical path between the viewfinder and
the lens assembly, optical compression and frame indicators (guidelines) are used to
approximate the image’s frame. This approximation often causes subtle differences
between what the photographer sees in the viewfinder and what is captured in the
image. This is especially noticeable when the subject is close to the camera.
10 Chapter 1
How Digital Cameras Capture Images
Camera Components and Concepts
The basic components of a DSLR are described below. (Most of the components in a
rangefinder are also found in a DSLR.)
Â
Lens
Â
Aperture
Â
Shutter
Â
Digital image sensor
Â
Memory card
Â
External flash
Lens
A lens is a series of sophisticated elements, usually glass, constructed to refract and
focus the reflective light from a scene at a specific point—the digital image sensor.
LCD display
Viewfinder
Light source
LensDigital image sensor
Reflective
light
Beyond framing an image, the first interaction you have with the reflective light from
your subject is through your camera’s lens.
Chapter 1
How Digital Cameras Capture Images
11
Focal Length
An important attribute of a lens, besides its quality, is its focal length.
Focal length
is
technically defined as the distance from the part of the optical path where the light
rays converge to the point where the light rays passing through the lens are focused
onto the image plane—or the digital image sensor. This distance is usually measured in
millimeters. From a practical point of view, focal length can be thought of as the
amount of magnification of the lens. The longer the focal length, the more the lens
magnifies the scene. In addition to magnification, the focal length determines the
perspective and compression of the scene.
Digital image sensor
Focal length Light
Lens
Camera body
(side view)
Understanding Lens Multiplication with DSLRs
Most interchangeable lenses were originally created and rated for the 35 mm film
plane of traditional SLRs. If you compare the area of a 35 mm film plane with the area
of most digital image sensors’ image planes, you’ll see that the area of most digital
image sensors is a bit smaller. The focal length of a lens changes when it is put on a
DSLR with a digital image sensor smaller than 35 mm. This smaller image plane
effectively increases the focal length of the lens because more of the image circle
coming out of the lens is cropped. For example, if you put a 100 mm lens on a DSLR
that has a 24 mm digital image sensor, the focal length of the lens is multiplied by a
factor of approximately 1.3. A 100 mm lens with a 1.3x multiplication factor effectively
becomes a 130 mm lens (100 mm multiplied by 1.3).
Another reason to take lens multiplication into account is that shooting wide-angle
images becomes increasingly difficult when using cameras with smaller digital image
sensors. For example, if your digital image sensor is 24 mm, you require a lens with a
focal length less than 24 mm to achieve a wide-angle view. Check your camera
specifications for the size of your digital image sensor.
12 Chapter 1
How Digital Cameras Capture Images
Lens Types
Although there are many varieties of lenses, common lens types include telephoto, wideangle, zoom, and prime. All of these lenses perform the same basic function: they
capture the reflective light from the subject and focus it on the image sensor. However,
the way they transmit the light differs.
Note:
Although there are several subcategories and hybrids of these lens types, these
are the most basic.
Telephoto
A telephoto lens is a lens with a long focal length that magnifies the subject. Telephoto
lenses are typically used by sports and nature photographers who shoot their subjects
from great distances. Telephoto lenses are also used by photographers who want
greater control over limiting the depth of field (the area of an image in focus). The
larger aperture settings, combined with the long focal lengths of telephoto lenses, can
limit the depth of field to a small area (either the foreground, middle, or background of
the image). Small aperture settings, combined with long focal lengths, make objects in
the foreground and background seem closer together.
Wide-Angle
A wide-angle lens is a lens with a short focal length that takes in a wide view. Wideangle lenses are typically used when the subject is in the extreme foreground and the
photographer wants the background in focus as well. Traditionally, the focal length of a
wide-angle lens is smaller than the image plane. However, in the digital photography
age, the sizes of image sensors vary, and the lens multiplication factors of most DSLRs
increase the focal length. Check the specifications of your camera to ascertain the size
of your digital image sensor. If the size of your digital image sensor is 28 mm, you
require a lens with a focal length less than 28 mm to achieve a wide-angle view.
Chapter 1
How Digital Cameras Capture Images
13
Zoom
A zoom lens, also known as an
its focal length. A zoom lens can be extremely convenient, because many zoom lenses
can change their focal lengths from wide-angle to standard and from standard to
zoom. This eliminates the need to carry and change multiple lenses while shooting a
subject or project. However, because of the movement between focal lengths, the
f-stops aren’t always entirely accurate. To achieve a greater level of accuracy with
apertures, many manufacturers have multiple minimum aperture values as the lens
moves from a shorter focal length to a longer one. This makes the lens slower at longer
focal lengths. (See “Understanding Lens Speed” on page 15 for an explanation of lens
speed.) Plus, a zoom lens requires additional glass elements to correctly focus the light
at different focal lengths. It is desirable to have the light pass through the least amount
of glass in order to obtain the highest-quality image possible.
optical zoom lens,
has the mechanical capacity to change
Understanding Digital Zoom
The digital zoom feature offered by some camera models does not really zoom in
closer to the subject. Digital zoom crops into the center area of the captured frame,
effectively enlarging the pixels. This results in a picture with a lower overall image
quality. If you don’t have a telephoto or optical zoom lens and you want a close-up,
physically move closer to the subject, if you can.
Prime
A prime lens, also known as a
Prime lenses often have wider maximum apertures, making them faster. For more
information about lens speed, see “Understanding Lens Speed” on page 15. Wider
apertures allow for brighter images in low-light situations, as well as greater control
over depth of field. Prime lenses are primarily used by portrait photographers. For more
information on depth of field, see “Depth of Field” on page 15.
fixed lens,
has a fixed focal length that is not modifiable.
Aperture
The aperture is the opening in the lens (created by an adjustable iris or diaphragm) that
allows light to pass through. The exposure of the image is determined by the
combination of shutter speed and the opening of the aperture. The larger the aperture,
the more light is allowed to pass through the lens. The aperture is measured in f-stops,
and each stop represents a factor of two in the amount of light admitted. The aperture
setting (f-stop), combined with the focal length of the lens, determines the depth of field
of an image. For more information on depth of field, see “Depth of Field” on page 15.
14 Chapter 1
How Digital Cameras Capture Images
f-stop
The photographer adjusts the opening of the aperture by setting the f-stop. An f-stop
is a ratio of the focal length of the lens to the diameter of the opening of the aperture.
For example, a 50 mm lens with an aperture opened up to a diameter of 12.5 mm
results in an f-stop of f4 (50 ÷ 12.5 = 4). Therefore, the larger the numerical value of the
f-stop, the smaller the opening of the aperture. The speed of a lens is determined by its
largest f-stop value (smallest number). Thus, the larger the aperture, the faster the lens.
f2 f2.8 f4 f5.6
f8 f11 f16 f22
Understanding Lens Speed
A lens’s speed is determined by the maximum amount of light the lens is capable of
transmitting—the largest f-stop value. When a lens is capable of transmitting more light
than other lenses of the same focal length, that lens is referred to as
allow photographers to shoot at higher shutter speeds in low-light conditions. For
example, lenses with maximum f-stop values between 1.0 and 2.8 are considered fast.
Depth of Field
Depth of field is the area of the image that appears in focus from foreground to
background and is determined by a combination of the opening of the aperture and
the focal length of the lens. A small aperture setting results in greater depth of field.
Controlling depth of field is one of the easiest ways for a photographer to compose the
image. By limiting the depth of field of an image, the photographer can turn the
attention of the viewer on the subject in focus. Often, limiting the depth of field of an
image helps eliminate clutter in the background. On the other hand, when shooting a
landscape, you want the image to have great depth of field. Limiting the depth of field
to the foreground would not make sense.
fast
. Fast lenses
Chapter 1
How Digital Cameras Capture Images
15
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