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Canon Digital SLR
Controls on the top of the EOS 350D are all found on the right side within reach of your index
finger or thumb. At the back of this shot we can see the shutter release button (soft half-press,
click full-press), main dial, exposure mode dial, power switch and two 'under your thumb
buttons'; AE lock and AF point select. Note that the drive button has moved from the top to the
rear of the camera.
Basic zone exposure modes
Full Auto and the six scene exposure modes are collectively referred to as the 'Basic Zone'. In all
of these modes the following camera options are either disabled or limited to:
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Icon
Description
P
Program Auto Exposure (Flexible)
Very similar to AUTO exposure but you have access to all the normal manual
controls, can set the ISO, exposure compensation, use AE lock, bracketing
etc. The Program AE on the EOS 350D is flexible, that means that you can
select one of a variety of equal exposures by turning the main dial. Example:
• 1/30 F2.8 (metered)
• 1/20 F3.2 (turn left one click)
• 1/15 F4.0 (turn left two clicks) etc.
Tv
Shutter Priority Auto Exposure
In this mode you select the shutter speed and the camera will calculate the
correct aperture for the exposure (depending on metered value; metering
mode, ISO). Shutter speed is displayed on the viewfinder status bar and on
the LCD panel, turn the main dial to select different shutter speeds. A halfpress of the shutter release causes the cameras exposure system to calculate
the aperture, if it's outside of the cameras exposure range the aperture will
blink. Available shutter speeds below represent 1/3 stop increments, 1/2
stop increments can be selected via custom function 6.
1/4000, 1/3200, 1/2500, 1/2000, 1/1600, 1/1250, 1/1000, 1/800, 1/640,
1/500, 1/400, 1/320, 1/250, 1/200, 1/160, 1/125, 1/100, 1/80, 1/60, 1/50,
1/40, 1/30, 1/25, 1/20, 1/15, 1/13, 1/10, 1/8, 1/6, 1/5, 1/4, 0.3, 0.4, 0.5,
0.6, 0.8, 1, 1.3, 1.6, 2, 2.5, 3.2, 4, 5, 6, 8, 10, 13, 15, 20, 25, 30 sec
Av
Aperture Priority Auto Exposure
In this mode you select the aperture and the camera will calculate the correct
shutter speed for the exposure (depending on metered value; metering mode,
ISO). Aperture is displayed on the viewfinder status bar and on the LCD
panel, turn the main dial to select different apertures. A half-press of the
shutter release causes the cameras exposure system to calculate the shutter
speed, if it's outside of the cameras exposure range the shutter speed will
blink. Available apertures will differ depending on the lens used, the list
below represent 1/3 stop increments, 1/2 stop increments can be selected
via custom function 6.
F1.0, F1.1, F1.2, F1.4, F1.6, F1.8, F2.0, F2.2, F2.5, F2.8, F3.2, F3.5, F4.0, F4.5,
F5.0, F5.6, F6.3, F7.1, F8.0, F9.0, F10, F11, F13, F14, F16, F18, F20, F22, F25,
F29, F32, F36, F40, F45, F51, F57, F64, F72, F81, F91 (exact range depends on
lens used)
M
Full Manual Exposure
In this mode you select the aperture and the shutter speed from any
combination of the above (plus BULB for shutter speed, apertures limited by
the lens used). Turn the main dial to select shutter speed, hold the exposure
compensation button and turn the main dial to select aperture. If you change
the exposure the meter graphic on the viewfinder status bar and LCD panel
will reflect the exposure level compared to the calculated ideal exposure, if
it's outside of +/- 2EV the indicator bar will blink either + or -.
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Ok by this time you should have a reasonable understanding of the basic technical
aspects of photography.
To recap we have covered the fundamentals of what need to know to get the correct
exposure, namely:
The Amount of Light - measured in EV
Film or chip sensitivity- measured in ISO
Aperture - measured in f/stops
Shutter-speed - measured in seconds
Correct Exposure
The correct exposure for any scene is the exposure that gives the picture you want. For
some scenes there may be a range of possible exposures that will work. Other scenes
may have a greater range of light levels that the camera and film or sensor can cope
with, and you need to chose the best exposure possible. Sometimes photographers will
deliberately give a technically incorrect exposure to get the artistic effect they want.
Think of exposure like filling a cup of water, the tap is the aperture, and the time the
tap is on the shutter speed. To get the right exposure (fill the cup) the tap full on (wide
open) needs 5 seconds worth of time. If we have the tap half open we need to
compensate by increasing the time.
LIght
The amount of light (brightness) determines what combinations of apertures and shutter
speeds we can use. Light is given a value determined by the brightness of the scene this
is known as the exposure value EV
Film or chip sensitivity
We have learned that film is produced in different sensitivities (how much light they
need) and is given an ISO value according to how sensitive it is - with 50 being the least
sensitive and 1600 being the most sensitive.
We have discovered sensitivity comes with a price however - the more sensitive the film
is the larger the crystals in the film have to be resulting in less detailed (grainy)lower
quality images. With digital the same rules apply however instead of grain we
experience higher noise.
ISO values
50
100
200
400
800
1600
-
Very fine grain - high quality
fine grain - good quality
good compromise grain - good quality
medium grain reasonable quality
coarse grain useable quality
Very coarse grain useable quality
The relationship between ISO speeds also double or half the sensitivity of the chip or
film with ISO 200 being twice as sensitive as ISO 100 or 1 stop faster or +1EV more
sensitive.
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Apertures
We have learned that the aperture is a variable hole in the lens much like the iris in
your eye and controls the amount of light traveling through the lens. In most lenses the
aperture is varied in size by a controllable iris, although some simple cameras use a
fixed aperture. The variable aperture allows the camera to work under different lighting
conditions.
Apertures are also given values namely f/stops the smaller the number the larger the
opening.
f/2 being the widest with f/22 being the smallest. Each half's or doubles the amount of
light reaching the film. Aperture Values are usually:
f/2.0, f/2.8, f/ 4, f/ 5.6, f/ 8, f/ 11, f/ 16, f/ 22
Each stop half's or doubles the amount of light reaching the film. 1 stop =1 EV
Confusingly for beginners, the smallest number in the series lets through the most light,
with each value to the right resulting in a halving of light. Photographers call each step
in this series a one stop difference or one EV.
F/2.8
F/22
So a smaller aperture is represented by a larger f number.
Stopping down a lens from full aperture cuts down the amount of light it passes, but
also has other effects. All lenses have inherent defects or aberrations and most (but not
all) of these are reduced by stopping down.
Shutter speed
The camera shutter also controls the amount of light reaching the film.
shutter speeds are given values between whole numbers and fractions. ie 2 seconds lets
twice as much light through than 1 second and 1/2 second lets half as much light .
shutter speed values are usually:
1 sec 1/2 sec 1/4 1/8 1/15 1/30 1/60 1/125/ 1/250 1/500/ 1/1000
Each speed in this series is (roughly or exactly) half that to the left, giving a halving in
the amount of light reaching the film. Each half's or doubles the amount of light
reaching the film.
We have also covered the relationship between aperture and shutters peed to control
depth of field and motion in the subject. Rember the two main things you need to
control in the subject are:
Movement- governed by the shutter speed
Depth of field (ie how much is sharp) governed by the aperture.
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Equivalent Exposures
When making settings using the P or Auto Modes, there are almost always a number of
equivalent exposures that can be used, with different combinations of aperture and
shutter speed admitting the same amount of light to the film (or sensor.)
For example, if the meter reading shows 1/125 f8, then the following settings would
give the same exposure:
1/15 f22 1/30 f16 1/60 f11 (1/125 f8;) 1/250 f5.6 1/500 f4 1/1000 f2.8
If you were using a telephoto lens, then you would want to avoid 1/30 f16 if the camera
was hand held or the subject moving at all. However it would be a good setting to pick
if you were using a standard lens and needed maximum depth of field.
However if you were photographing motorcycle stunt riders with rapid movement you
might want a faster shutter speed, perhaps 1/500 f4.
With automatic exposure cameras, the choice of equivalent exposures is often handled
by using either a shutter priority or an aperture priority auto exposure mode. These
allow you to choose either the shutter speed or aperture setting. Normally in
programmed mode the camera makes both choices
Choice of Shutter Speeds
Choosing correct shutter speed is important in making sure you avoid camera shake or
blurring of moving objects. You can usually avoid shake by using a shutter speed faster
than that based on putting the '35mm equivalent focal length' of the lens you are using
into the formula: 1/focal length.
Auto or Manual Control
Most modern cameras have auto exposure and automatically control the lens aperture
when in program mode. Some will have aperture, shutter priority(TV) or manual modes
that leave control of aperture - sometimes by a ring around the lens, but usually by a
button on the camera - to the photographer.
Using f stops
Depth of Field
Stopping down also increases the zone of sharpness in front and behind the actual
distance the lens is focussed on, which is usually useful. This zone is called the depth of
field. Occasionally we want to make use of limited depth of field for emphasis.
However, stopping down reduces the amount of light, and we have to increase the
exposure time to compensate. Too long an exposure can give camera shake or allow
moving objects to record as a blur.
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