What is Focus -- The standard definitions of focus are: 1) The position at which rays of light from
a lens converge to form a clear and sharply defined image on a focal plane. 2) The action of
adjusting the distance between the lens and subject to make light rays converge to form a clear and
sharply defined image of the subject.
What is a Camera Shutter and shutter speed ?
Before reading this article, I highly recommend reading about what a DSLR is and what it
consists of. Simply put, a camera shutter is a curtain in front of the camera sensor that stays
closed until the camera fires. When the camera fires, the shutter opens and fully exposes the
camera sensor to the light that passes through the lens aperture. After the sensor is done
collecting the light, the shutter closes immediately, stopping the light from hitting the
sensor. The button that fires the camera is also called “shutter” or “shutter button”,
because it triggers the shutter to open and close.
Shutter speed, also known as “exposure time”, stands for the length of time a camera
shutter is open to expose light into the camera sensor. If the shutter speed is fast, it can
help to freeze action completely, as seen in the above photo of the dolphin. If the shutter
speed is slow, it can create an effect called “motion blur”, where moving objects appear
blurred along the direction of the motion. This effect is used quite a bit in advertisements
of cars and motorbikes, where a sense of speed and motion is communicated to the viewer
by intentionally blurring the moving wheels.
The look of a photograph is affected by a variety of factors, including shutter speed, aperture, and ISO sensitivity.
This guide gives beginners a grasp of the basics with easy-to-understand explanations of the features and design
of digital single-lens reflex cameras
What is Exposure---In photography, exposure is the amount of light per unit area (the image
planeilluminance times the exposure time) reaching a photographic film, as determined by shutter
speed, lens aperture and scene luminance. In digital photography "film" is substituted with "sensor".
Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene
luminance in a specified region.
In photographic jargon, an exposure generally refers to a single shutter cycle. For example: a long
exposure refers to a single, protracted shutter cycle to capture enough low-intensity light, whereas
a multiple exposure involves a series of relatively brief shutter cycles; effectively layering a series of
photographs in one image. For the same film speed, the accumulated photometric exposure (Hv)
should be similar in both cases.
Control
Focus
Description
The position of a viewed object or the adjustment of an optical device necessary to
produce a clear image: in focus; out of focus.[28]
Adjustment of the lens opening, measured as f-number, which controls the amount
of light passing through the lens. Aperture also has an effect on depth of
Aperture
field and diffraction – the higher the f-number, the smaller the opening, the less light,
the greater the depth of field, and the more the diffraction blur. The focal length
divided by the f-number gives the effective aperture diameter.
Adjustment of the speed (often expressed either as fractions of seconds or as an
angle, with mechanical shutters) of the shutter to control the amount of time during
Shutter speed
which the imaging medium is exposed to light for each exposure. Shutter speed may
be used to control the amount of light striking the image plane; 'faster' shutter
speeds (that is, those of shorter duration) decrease both the amount of light and the
amount of image blurring from motion of the subject and/or camera.
Metering
Measurement of exposure so that highlights and shadows are exposed according to
the photographer's wishes. Many modern cameras meter and set exposure
automatically. Before automatic exposure, correct exposure was accomplished with
the use of a separate light metering device or by the photographer's knowledge and
experience of gauging correct settings. To translate the amount of light into a usable
aperture and shutter speed, the meter needs to adjust for the sensitivity of the film or
sensor to light. This is done by setting the "film speed" or ISO sensitivity into the
meter.
Traditionally used to "tell the camera" the film speed of the selected film on film
cameras, ISO speeds are employed on modern digital cameras as an indication of
the system's gain from light to numerical output and to control the automatic
ISO speed
exposure system. The higher the ISO number the greater the film sensitivity to light,
whereas with a lower ISO number, the film is less sensitive to light. A correct
combination of ISO speed, aperture, and shutter speed leads to an image that is
neither too dark nor too light, hence it is 'correctly exposed', indicated by a centered
meter.
On some cameras, the selection of a point in the imaging frame upon which the
Autofocuspoint auto-focus system will attempt to focus. Many Single-lens reflex cameras (SLR)
feature multiple auto-focus points in the viewfinder.
1
Depth of Field
Depth of Field (DOF) is the front-to-back zone of a photograph in which
the image is razor sharp. As soon as an object (person, thing) falls out of
this range, it begins to lose focus at an accelerating degree the farther out
of the zone it falls; e.g. closer to the lens or deeper into the background.
With any DOF zone, there is a Point of Optimum focus in which the object
is most sharp. There are two ways to describe the qualities of depth of
field - shallow DOF or deep DOF. Shallow is when the included focus
range is very narrow, a few inches to several feet. Deep is when the
included range is a couple of yards to infinity. In both cases DOF is
measured in front of the focus point and behind the focus point. DOF is
determined by three factors – aperture size, distance from the lens, and
the focal length of the lens. Let’s look at how each one works.
2
Aperture
The aperture is the opening at the rear of the lens that determines how
much light travels through the lens and falls on the image sensor. The
size of the aperture’s opening is measured in f-stops - one of two sets of
numbers on the lens barrel (the other being the focusing distance). The f stops work as inverse values, such that a small f/number (say f/2.8)
corresponds to a larger or wider aperture size, which results in a shallow
depth of field; conversely a large f/number (say f/16) results in a smaller
or narrower aperture size and therefore a deeper depth of field.
3
Small vs Large Aperture
Manipulating the aperture is the easiest and most often utilized means to
adjust Depth of Field. To achieve a deep, rich and expansive DOF, you’ll
want to set the f-stop to around f/11 or higher. You may have seen this
principle demonstrated when you look at photos taken outside during the
brightest time of the day. In such a case, the camera is typically set at f/16
or higher (that Sunny 16 Rule) and the Depth of Field is quite deep perhaps several yards in front of and nearly to infinity beyond the exact
focus point. Let’s take a look at these two photos as examples. The photo
on the left has an expansive DOF, most likely shot around noon (notice
the short, but strong shadows), with an f/22 aperture. The photo on t he
right has an extremely shallow DOF; probably an f/2.8 aperture setting.
4
Aperture Range
The aperture range identifies the widest to smallest range of lens
openings, i.e. f/1.4 (on a super-fast lens) to f/32, with incremental “stops”
in between (f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, and f/22). Each f-number is
represents one “stop” of light, a stop is a mathematical equation (which is
the focal length of the lens divided by the diameter of the aperture
opening) that determines how much light that enters the lens regardless of
the length of the lens. Such that an f/4 on a 50mm has smaller opening
than an f/4 on a 200mm, but an equivalent amount of light travels through
both lenses to reach the image sensor thus providing the same exposure.
Each movement up the range (say f/2 to f.2.8) reduces the amount of light
by one-half and each movement down the range (say f/11 to f/8) doubles
the amount of light passing through the lens. It’s important to understand
this concept and how it affects exposure because it works in tandem with
the shutter speed (we’ll discuss this in another section) to establish a
given exposure value. Basically, when you change the aperture size one
stop, you have to shift the shutter speed one stop in the opposite direction
to maintain a consistent exposure… and this change in aperture alters the
depth of field (DOF) accordingly.
5
Distance from the Lens
The last element affecting depth of field is the distance of the subject from
the lens - you can adjust the DOF by changing that distance. For
example, the closer an object is to the lens (and the focus is set on that
object) the shallower the DOF. Conversely, the reverse is true - the farther
away an object is and focused on, the deeper the DOF. Changing the
distance to subject is the least practical way to manipulate the depth of
field, and by changing the distance from a subject to the lens, you
immediately change your image’s composition. To maintain the
compositional integrity of the shot, but still have the change in DOF from a
distance, you can change the focal length (either by changing lenses or
zooming in). Why does changing the focal length negate the effects on
DOF? This is because the visual properties of a given lens either provide
either greater DOF (shorter lenses) or shallower DOF (longer lenses). The
physical properties of a lens at a given focal length also affect the depth
of field. A shorter focal length lens (say 27mm) focused at 5 meters, set at
f/4 has a deeper DOF (perhaps from 3 meters in front and 20 meters
behind) than a longer focal length (say 300mm), also set at f/4 focused at
5 meters. The 300mm lens has a remarkably shallow depth of field.
Incidentally, to help you with this, every lens has a manual with a DOF
chart for each f/stop and the major focusing distances. DOF is just a
matter of physics, and it’s important to grasp this concept.
What is ISO---Photography is built on the three pillars of exposure: shutter speed,
aperture and sensitivity. Shutter and aperture are controls for adjusting how much light
comes into the camera. How much light is needed is determined by the sensitivity of the
medium used. That was as true for glass plates as it is for film and now digital sensors.
Over the years that sensitivity has been expressed in various ways, most recently as
ASA and now ISO.
The "normal" range of ISO is about 100 to 1600. With today's digital cameras you can
sometimes go as low as 50 or as high as 204,800. The number chosen has two
important qualities associated with it. First, it sets the amount of light needed for a good
exposure. The lower the number, the more light required. The more light that's required,
the more likely a slow shutter speed will have to be used. That means low ISOs, like
100 or 200, are most often used in bright situations (like sunlight) or when the camera is
mounted on a tripod. If you don't have a lot of light, or need a fast shutter speed, you
would probably raise the ISO.
Each time you double the ISO (for example, from 200 to 400), the camera needs only
half as much light for the same exposure. So if you had a shutter speed of 1/250 at 200
ISO, going to 400 ISO would let you get the same exposure at 1/500 second (providing
the aperture remains unchanged). This is why high ISOs are so often used indoors,
especially at sporting events. Needing a fast shutter speed to stop action,
photographers regularly choose ISO 1600 or above.
Types of Camera Lens
There are dozens of different types of lens available, designed for use in a wide range of
circumstances. However, they can largely be grouped in three major types depending on the
focal length they contain, those are as follows :
1) Normal Lens or Standard Lenses :-
A standard lens is one with a mid-range focal length, typically around 50mm(specified for 35mm
sensor). They have an angle of view which is roughly the same as the angle that the human eye
can comfortably view, meaning that they produce images which appear "natural" to the viewer.
Standard camera lenses usually have a fixed focal length and wide aperture, giving them
excellent performance in low light. They are popular for a wide range of photography subjects,
including landscapes, portraits, and candid shots.
2) Telephoto Lenses:-
A telephoto lens has a long focal length and provides a high level of magnification, allowing you
to photograph subjects at a moderate to far distance. They tend to be bigger and heavier than
other types of lens, although modern technological advances have made them more compact and
easier to handle.
Telephoto lenses are popular for any type of photography where you can't get near to the subject,
including wildlife and sports events. They are also commonly used in portrait photography,
where a moderate telephoto lens will provide a natural, undistorted perspective.
3) Wide Angle Lenses :-
A wide angle lens is one with a short focal length. They provide an angle of view beyond that of
a standard lens, allowing them to capture more of the scene in a single shot. Extreme wide angle
lenses are known asfisheye lens; these can capture around 180 degrees, making for some
intriguing, almost abstract photos.
Wide angle lenses are useful for photographing landscapes, cramped interiors, and other subjects
which won't fit into a normal lens's field of view. Fisheye lenses take this even further, and are
popular for photographing action sports like skateboarding and surfing, where their inherent
distortion gives photos a dynamic feel.
Zoom Lens and Prime Lens
Zoom Lenses: The lens which contain varriable focal length (thus varriable angle of views) such types
of lenses are known as zoom lens . It may contain above mentioned all three
characteristics of lens ( i.e Wide lens , telephoto lens, and normal lens) Now a days
zoom lenses are widely used for the photography or photojournalism purpose .
Prime Lens or Block Lens:The type of lenses in which the focal length doesnot varry or in the other words we can
say that the angle of view remains constant , those type of lenses are known as prime
or block lens.
ColourIn photography we majorly deal with primary colour , since our eye vision is trichromatic
The primary colours are of three types , those are as follows—
1) Red
2) Green
3) Blue
Apart from the primary colours there are secondary colours & those are essential in photography
. Secondary colours are also three types , By combining any two of the primary colours we can
get one secondary colour ,
1) Yellow= Red+Green
2) Megenta= Red+Blue
3) Cyan= Blue+Green