basics of photography 1
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BASICS OF PHOTOGRAPHY
Focal Length
When parallel rays of light strike a lens focused at infinity, they converge to a point
called the focal point. The focal length of the lens is then defined as the distance
from the middle of the lens to its focal point.
The focal length of a lens is usually displayed on the lens barrel. Below is a picture
of a Canon lens with a focal length of 50mm. The maximum aperture is f/1.8.
Lenses are usually categorized as having a wide-angle, normal or telephoto focal
length. A normal SLR lens covers a 24x36mm film frame with a field of view that
corresponds approximately to our normal vision; a lens with a focal length of 50mm
(55mm is also popular) is considered as normal.
Any lens with a focal length less than 50mm (or 55mm) can be considered as wide-
angle; any lens with a focal length greater than 50mm (or 55mm) can be considered
a telephoto. A zoom lens offers a range of focal lengths. This table lists some of themore popular focal lengths:
Lens Popular Focal Lengt hs for 35m m c am er as
Wide-angle 18mm, 20mm, 28mm, 35mm
Normal 50mm, 55mm
Telephoto 90mm, 135mm, 200mm, 300mm
Take a look at the two Nikon lenses below; the lens on the left is an SLR camerazoom lens with a focal length of 28-105mm. This is a popular zoom lens because it
provides a good wide-angle (28mm) as well as enough telephoto reach for a good
portrait (with 105mm, you can fill the screen with a face without getting in your
subject's face, so to speak).
The lens on the right comes with the Nikon Coolpix 5400 digital camera and has
zoom focal lengths of 5.8-24mm. Believe it or not, this is the equivalent of 28-
116mm zoom lens on a 35mm SLR camera! (The Coolpix 5400 no longer seems to
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be available although accessories for it are, but you might track one down for a good
price on eBay.)
N i k on 28 - 105m mf / 3 .5 -4 .5D AF-Zoom N ikkor
Nikon Coo lp ix 5400: 5 .8 -24 mm( 28 - 116m m , 35m m equ i v al en t )
f / 2 . 8 - 4 .6 Z oom N i k k o r ED
Because the image sensor size used in digital cameras are of different sizes, the same
focal lengths may be expressed using different numeric values. Smaller image
sensors require smaller lenses; larger image sensors require larger lenses to ensure all
the surface of the image sensor is covered. Other factors, such as the amount of
optical zoom provided, may further affect the distance between lens and the image
sensor.
It's more convenient to use the SLR equivalent as a handy reference point. Most, if
not all, camera manufacturers will list the 35mm SLR equivalent in the
specifications of a digital camera. Interestingly, some digital cameras are now even
engraved with the 35mm equivalent on the lens barrel to express the focal length of
the lens. It makes more sense in a way, though it is important to bear in mind that
35mm equivalent does not mean 100% compatibility with the real SLR lens. This is
especially true in the area of depth of field.
If you use a digital SLR (dSLR) that uses lenses made for 35mm film cameras, you
need to be aware that the focal lengths expressed on the lenses must be multiplied by
a factor. That factor, the Focal Length Multiplier, depends on the image sensor size
used (that will be in the Specifications section of your camera manual).
Of course, if the image sensor is full-frame, i.e. it is the same size as 35mm film,
then the multiplier is 1, and the focal length of the lens is accurate.
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However, only a few dSLRs use a full-frame image sensor (such cameras are beyond
the budget of hobbyist photographers, being in the range of several thousands of
dollars), with most using a smaller image sensor, usually APS size (or roughly half-
frame). That's why you'll read that a focal length multiplier of, say, 1.6 needs to be
applied to the focal length of the lens to obtain the true focal length.
So, suppose your dSLR has a Focal Length Multiplier of 1.6 and you use a 50mm
lens with it, the actual focal length of the lens when used with your dSLR is 1.6 x
50mm = 80mm. This is both good and bad. The good news is that you can now get
super telephoto focal lengths on your dSLR without buying costly and unwieldly
dedicated lenses. For example, a 100-300mm zoom lens, with a focal length
multiplier of 1.6, becomes approx. 160-480mm. The bad news is, of course, that
super wide-angle lenses are equally affected and a 28mm lens becomes a 45mm lens.
One solution is to buy a 16mm fisheye lens which, when factored up by 1.6,
becomes a 26mm lens.
To confuse matters even more, 'digital' lenses are appearing (or sold along with
digital camera bodies) which show the digital focal length range rather than the SLR
equivalent. Canon provide an 18-55mm lens with their EOS digital range of cameras.
While this is equivalent to a 35mm SLR range of 29mm-56mm, that equivalent
range isn't printed on the lens. A little experience will let you identify 35mm SLR
lenses from lenses specifically designed for use with dSLRs.
Lens Terminology
EF - The EF lens mount allows all the Canon EF lenses to be used on any of theCanon EOS. EF stands for Electro-Focus: automatic focusing on EF lenses ishandled by a dedicated electric motor built into the lens. All communication
between camera and lens takes place through electrical contacts; there are no
mechanical levers or plungers.
USM - Ultrasonic motor drive - EF lenses equipped with USM drives have fast,silent and precise auto focus operations, and consume less power compared to
other AF drive motors. There are two types of USMs, the ring-type USM and the
micromotor USM. Ring-type USM is always preferred because of its superiorperformance and efficiency, and it allows for full-time manual focus operations
without switching out of AF mode.
IS - Image stabilizer - the Image Stabilizer (IS) counters camera movements andshakes by optically correcting such shakes with accelerometers and lens groups
that move in relation to the shakes, thus minimizing or even eliminating minute
vibrations from the image. A general rule-of-thumb to overcome such vibrations
would be to set the shutter speed equal to or faster than the reciprocal of the lens
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focal length (e.g. 1/125s for a 100 mm lens). IS lenses can improve on this rule by
up to three stops. That is, the same 100 mm lens could be used at 1/30s.
L - series lenses - top of the line Canon EF lenses are designated as L-series. L-series lenses have superior optical performance and are typically built with a solid
construction to withstand constant use and harsh conditions. They can be
recognized by a red ring around the front part of the lens. Most recent L lenses
have sealing to help resist dust and water. L-series lenses are more frequently
used by professionals and serious amateurs due to their high price and large mass.
EF-S - The lens mount is a derivative of the EF lens mount created for a subsetof Canon digital single-lens reflex cameras with APS-C sized image sensors.
The three basic lens types, determined by the focal length (measured in millimeters)
of the lenses, are the following:
Normal - A normal lens shows mostaccurately what a normal human eye
will see. 50mm is a typical normal
focal length. The 50mm is the most
popular and versatile lens. The quality
is excellent while also being
inexpensive. It is smaller and lighter,
and the aperture allows photographs to
be taken in low-light situations.
Telephoto - A telephone lens brings the
background closer. Longer-than-normal
focal lengths such as 70mm and
300mm are typical for a telephoto lens.
Since a telephoto lens will bring the
subject up close, it is popular for sportsphotography.
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Lenses come in either prime or zoom. Prime lenses have a fixed focal length. In
order to fit more or less into the viewfinder, the photographer must physically move
forward or backward. Focal length in a zoom lens can be changed by turning the
zoom ring on the lens. A zoom will have a variable focal length such as 28mm-
105mm. While zoom lenses are more convenient for storage and versatility, prime
lenses often have a sharper lens and work better in low-light situations.
In addition to focal length, consider the lens speed and its focusing distance. The lens
speed is determined by the f-stop setting. A faster lens will be heavier and more
expensive. The focusing distance is the distance from the lens to the subject needed
to achieve a focused photograph.
Other special lenses to consider include the following:
Macro. A macro lens's focus is closer to the subject and is used for close-upphotography.
Fisheye. A fisheye lens uses an angle of view up to 180 degrees. The angledistorts the photograph so the four sides appear to be farther away.
Teleconverter. A teleconverter attaches between the camera and another lens.It increases the focal length of your lens. Although teleconverters will bring
the subject closer, they do not allow as much light through the lens. Thus, they
need slower shutter speeds and/or a fast ISO.
Digital camera SLR users need to be aware of the focal length differences in lenses
that are interchangeable for film and digital cameras. All focal lengths listed on
interchangeable lenses are for film cameras. To get the true focal length of a digital
camera the number needs to be multiplied by 1.6. Remember that the lens won't be
as wide on a digital camera as you would get on a film camera using the same lens.
Wide - A wide lens captures a wider
expanse of the background than what
the human eye will see. Shorter-than-
normal focal lengths such as 24mm
and 35 mm are typical for a wide lens.
Wide lenses are popular for landscape
photography and large group shots.
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For example, the standard 50mm lens on a film camera is actually 80mm on a digital
camera.
When purchasing a new lens, first consider your needs. What will you be
photographing? The subjects of your photographs should dictate whether you need a
normal, telephoto or wide lens. Then, consider the trade-off between the optics
quality, the camera's weight, the convenience of a prime vs. a zoom lens, lens speed,
focal distance and price. Often it will be a balance of these considerations that leads
you to a good camera.
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Understanding ISO, Aperture and Shutter Speed
Each of the three aspects of the triangle relate to light and how it enters and interacts
with the camera.
The three elements are:
ISO the measure of a digital camera sensors sensitivity to light
Aperture the size of the opening in the lens when a picture is taken
Shutter Speed the amount of time that the shutter is open
It is at the intersection of these three elements that an images exposure is worked
out.
Most importantly a change in one of the elements will impact the others. This means
that you can never really isolate just one of the elements alone but always need tohave the others in the back of your mind.
The Window
Imagine your camera is like a window with shutters that open and close.
Aperture is the size of the window. If its bigger more light gets through and the
room is brighter.
Shutter Speed is the amount of time that the shutters of the window are open. The
longer you leave them open the more that comes in.
Now imagine that youre inside the room and are wearing sunglasses (hopefully this
isnt too much of a stretch). Your eyes become desensitized to the light that comes in
(its like a low ISO).
There are a number of ways of increasing the amount of light in the room (or at least
how much it seems that there is. You could increase the time that the shutters are
open (decrease shutter speed), you could increase the size of the window (increase
aperture) or you could take off your sunglasses (make the ISO larger).
Ok its not the perfect illustration but you get the idea.
BringingItAllTogetherMastering the art of exposure is something that takes a lot of practice. In many ways
its a juggling act and even the most experienced photographers experiment and
tweak their settings as they go. Keep in mind that changing each element not only
impacts the exposure of the image but each one also has an impact upon other
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aspects of it (i.e. changing aperture changes depth of field, changing ISO changes the
graininess of a shot and changing shutter speed impacts how motion is captured).
The great thing about digital cameras is that they are the ideal testing bed for
learning about exposure. You can take as many shots as you like at no cost and they
not only allow you to shoot in Auto mode and Manual mode but also generally
have semi-automatic modes like aperture priority and shutter priority modes which
allow you to make decisions about one or two elements of the triangle and let the
camera handle the other elements.
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What is ISO?
In traditional (film) photography ISO (or ASA) was the indication of how sensitive a
film was to light. It was measured in numbers (youve probably seen them on films
100, 200, 400, 800 etc). The lower the number the lower the sensitivity of the film
and the finer the grain in the shots youre taking.
In Digital Photography ISO measures the sensitivity of the image sensor. The same
principles apply as in film photography the lower the number the less sensitive
your camera is to light and the finer the grain. Higher ISO settings are generally used
in darker situations to get faster shutter speeds (for example an indoor sports event
when you want to freeze the action in lower light) however the cost is noisier shots.
Ill illustrate this below with two elargements of shots that I just took the one on
the left is taken at 100 ISO and the one of the right at 3200 ISO (click to enlarge to
see the full effect).
100 ISO is generally accepted as normal and will give you lovely crisp shots (littlenoise/grain).
Most people tend to keep their digital cameras in Auto Mode where the camera
selects the appropriate ISO setting depending upon the conditions youre shooting in
(it will try to keep it as low as possible) but most cameras also give you the
opportunity to select your own ISO also.
When you do override your camera and choose a specific ISO youll notice that it
impacts the aperture and shutter speed needed for a well exposed shot. For example
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if you bumped your ISO up from 100 to 400 youll notice that you can shoot at
higher shutter speeds and/or smaller apertures.
When choosing the ISO setting I generally ask myself the following four questions:
1. Light Is the subject well lit?2. Grain Do I want a grainy shot or one without noise?3. Tripod Am I using a tripod?4. Moving Subject Is my subject moving or stationary?
If there is plenty of light, I want little grain, Im using a tripod and my subject is
stationary I will generally use a pretty low ISO rating.
However if its dark, I purposely want grain, I dont have a tripod and/or my subject
is moving I might consider increasing the ISO as it will enable me to shoot with a
faster shutter speed and still expose the shot well.
Of course the trade off of this increase in ISO will be noisier shots.
Situations where you might need to push ISO to higher settings include:
Indoor Sports Events where your subject is moving fast yet you may have limited
light available.
Concerts also low in light and often no-flash zones
Art Galleries, Churches etc- many galleries have rules against using a flash and of
course being indoors are not well lit.
Birthday Parties blowing out the candles in a dark room can give you a nice
moody shot which would be ruined by a bright flash. Increasing the ISO can help
capture the scene.
ISO is an important aspect of digital photography to have an understanding of if you
want to gain more control of your digital camera. Experiment with different settings
and how they impact your images today.
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What is Aperture?
Put most simply Aperture is the size of the opening in the lens when a picture is
taken.
When you hit the shutter release button of your camera a hole opens up that allows
your cameras image sensor to catch a glimpse of the scene you want to capture. The
aperture that you set impacts the size of that hole. The larger the hole the more light
that gets in the smaller the hole the less light.
Aperture is measured in f-stops. Youll often see them referred to here at Digital
Photography School as f/number for example f/2.8, f/4, f/5.6,f/8,f/22 etc. Moving
from one f-stop to the next doubles or halves the size of the amount of opening in
your lens (and the amount of light getting through). Keep in mind that a change in
shutter speed from one stop to the next doubles or halves the amount of light that
gets in also this means if you increase one and decrease the other you let the same
amount of light in very handy to keep in mind).
One thing that causes a lot of new photographers confusion is that large apertures
(where lots of light gets through) are given f/stop smaller numbers and smaller
apertures (where less light gets through) have larger f-stop numbers. So f/2.8 is in
fact a much larger aperture than f/22. It seems the wrong way around when you first
hear it but youll get the hang of it.
Depth of Field and Aperture
There are a number of results of changing the aperture of your shots that youll wantto keep in mind as you consider your setting but the most noticeable one will be the
depth of field that your shot will have.
Depth of Field (DOF) is that amount of your shot that will be in focus . Large depth
of field means that most of your image will be in focus whether its close to your
camera or far away (like the picture below where both the foreground and
background are largely in focus taken with an aperture of f/22).
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Small (or shallow) depth of field means that only part of the image will be in focus
and the rest will be fuzzy (like in the flower on top of). Youll see in it that the tip of
the yellow stems are in focus but even though they are only 1cm or so behind them
that the petals are out of focus. This is a very shallow depth of field and was taken
with an aperture of f/4.5).
Aperture has a big impact upon depth of field. Large aperture (remember its a
smaller number) will decrease depth of field while small aperture (larger numbers)
will give you larger depth of field.
It can be a little confusing at first but the way I remember it is that small numbers
mean small DOF and large numbers mean large DOF.
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Let me illustrate this with two pictures I took earlier this week in my garden of two
flowers.
The first picture below (click them to
enlarge) on the left was taken with an
aperture of f/22 and the second one wastaken with an aperture of f/2.8. The
difference is quite obvious. The f/22
picture has both the flower and the bud
in focus and youre able to make out the
shape of the fence and leaves in the
background.
The f/2.8 shot (2nd one) has the left
flower in focus (or parts of it) but the
depth of field is very shallow and the
background is thrown out of focus and
the bud to the right of the flower is also
less in focus due to it being slightly
further away from the camera when the
shot was taken.
The best way to get your head around aperture is to get your camera out and do some
experimenting. Go outside and find a spot where youve got items close to you as
well as far away and take a series of shots with different aperture settings from the
smallest setting to the largest. Youll quickly see the impact that it can have and the
usefulness of being able to control aperture.
Some styles of photography require large depths of field (and small Apertures)
For example in most landscape photography youll see small aperture settings (large
numbers) selected by photographers. This ensures that from the foreground to the
horizon is relatively in focus.
On the other hand in portrait photography it can be very handy to have your subject
perfectly in focus but to have a nice blurry background in order to ensure that your
subject is the main focal point and that other elements in the shot are not distracting.
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In this case youd choose a large aperture (small number) to ensure a shallow depth
of field.
Macro photographers tend to be big users of large apertures to ensure that the
element of their subject that they are focusing in on totally captures the attention of
the viewer of their images while the rest of the image is completely thrown out of
focus.
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Shutter Speed
Shutter speed is measured in seconds or in most cases fractions of seconds. The
bigger the denominator the faster the speed (i.e. 1/1000 is much faster than 1/30).
In most cases youll probably be using shutter speeds of 1/60th of a second or
faster. This is because anything slower than this is very difficult to use without
getting camera shake. Camera shake is when your camera is moving while the
shutter is open and results in blur in your photos.
If youre using a slow shutter speed (anything slower than 1/60) you will need to
either use a tripod or some type of image stabilization (more and more cameras are
coming with this built in).
Shutter speeds available to you on your camera will usually double
(approximately) with each setting. As a result youll usually have the options for
the following shutter speeds 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8 etc. This
doubling is handy to keep in mind as aperture settings also double the amount of
light that is let in as a result increasing shutter speed by one stop and decreasing
aperture by one stop should give you similar exposure levels (but well talk more
about this in a future post).
Some cameras also give you the option for very slow shutter speeds that are not
fractions of seconds but are measured in seconds (for example 1 second, 10 seconds,
30 seconds etc). These are used in very low light situations, when youre going after
special effects and/or when youre trying to capture a lot of movement in a shot).
Some cameras also give you the option to shoot in B (or Bulb) mode. Bulb mode
lets you keep the shutter open for as long as you hold it down.
When considering what shutter speed to use in an image you should always ask
yourself whether anything in your scene is moving and how youd like to capture
that movement. If there is movement in your scene you have the choice of either
freezing the movement (so it looks still) or letting the moving object intentionally
blur (giving it a sense of movement).
To freeze movement in an image (like in the surfing shot above) youll want tochoose a faster shutter speed and to let the movement blur youll want to choose a
slower shutter speed. The actual speeds you should choose will vary depending upon
the speed of the subject in your shot and how much you want it to be blurred.
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Motion is not always bad I spoke to one digital camera owner last week who told
me that he always used fast shutter speeds and couldnt understand why anyone
would want motion in their images. There are times when motion is good. For
example when youre taking a photo of a waterfall and want to show how fast the
water is flowing, or when youre taking a shot of a racing car and want to give it afeeling of speed, or when youre taking a shot of a star scape and want to show how
the stars move over a longer period of time etc. In all of these instances choosing a
longer shutter speed will be the way to go. However in all of these cases you need to
use a tripod or youll run the risk of ruining the shots by adding camera movement (a
different type of blur than motion blur).
Focal Length and Shutter Speed - another thing to consider when choosing shutter
speed is the focal length of the lens youre using. Longer focal lengths will
accentuate the amount of camera shake you have and so youll need to choose afaster shutter speed (unless you have image stabilization in your lens or camera). The
rule of thumb to use with focal length in non image stabilized situations) is to
choose a shutter speed with a denominator that is larger than the focal length of the
lens. For example if you have a lens that is 50mm 1/60th is probably ok but if you
have a 200mm lens youll probably want to shoot at around 1/250.
Shutter Speed Bringing it together
Remember that thinking about Shutter Speed in isolation from the other two
elements of the Exposure Triangle (aperture and ISO) is not really a good idea. As
you change shutter speed youll need to change one or both of the other elements to
compensate for it.
For example if you speed up your shutter speed one stop (for example from 1/125th
to 1/250th) youre effectively letting half as much light into your camera. To
compensate for this youll probably need to increase your aperture one stop (for
example from f16 to f11). The other alternative would be to choose a faster ISO
rating (you might want to move from ISO 100 to ISO 400 for example).