PHOTOGRAPHY
Duration of Examination: 3 hrs
Maximum Marks: 100
Credits: 4
Objective: To provide students with the knowledge of Photography and make best
use of it in Visual Communication
Unit 1:
History of Photography, Human Eye and Camera, Characteristics of
Light.
Unit 2:
Camera and Lens: Camera – Types of Camera, Structure and Features.
Lens – Types of lenses, Focal Length, Aperture and Angle of View.
Unit 3:
Chemistry of Photography: Light Sensitivity – Film and Paper,
Developer, Fixer and Other Chemicals, Basic Requirements of Photography,
Control Factors.
Unit 4:
Photographic Techniques: Exposure, Depth of Field, Action, etc,.
Aesthetics in Photography, Types of Photography: Photo Journalism, Event
Photography, etc,.
Unit 5:
Career in Photography: Newspaper, Advertisement Industry, Fashion
photography Tourism Photography, Science photography, Wild life photography etc.,
Reference:
q
John
Garrett, Guide to Photography, D.K. Publications (2004).
q
Micheal
Longford, Basic Photography course. Fireside Book New York (1979).
q
Steve
Luck, Foundation Course: Digital Photography, Octopus Publishing Group (2006).
http://vimeo.com/13927581
http://www.youtube.com/watch?v=hGu53xUzO0M
http://youtu.be/hGu53xUzO0M
PHOTOGRAPHY TERMS AND DEFINITIONS:
Aberration
An optical defect in a lens causing it to form an image that is not sharp or that is distorted. This can take the shape of edge distortion or a lack of sharpness.
Adobe RGB (1998)
The RGB working space created by Adobe Systems, incorporated that provides a fairly large gamut of colors and is well-suited for documents that will be converted to CMYK ... Generally speaking this is the setting recommended by most photographers.
AF (Autofocus) Lock
Used to prevent autofocus operation once the subject is in focus. This gives you more creative control by allowing you to focus, compose your image, and then capture the image.
Angle of View
The area of a scene that a lens can cover. The focal length of the lens determines the angle of view. A wide-angle (short-focal-length) lens includes more of a scene than a standard (normal-focal-length) lens or telephoto (long-focal-length) lens. Angle of view is basically the angle at which light rays can pass through the lens to produce an image on the film.
Aperture
The aperture is the opening formed by the blades of the iris or diaphragm in the lens, through which light passes to expose the film. Aperture size is usually given in f-numbers, the larger the number, the smaller the opening. Aperture size together with shutter speed determine the amount of light falling on the film (exposure). The aperture is sometimes called the “stop".
Aspherical lens
A lens with a curved, non-spherical surface. Used to reduce aberrations and achieve a more compact lens size. With a spherical lens, rays traveling from the lens periphery create the image before the ideal focal point and give a blurred image center. With an aspherical lens, even the rays traveling from the lens periphery converge at the ideal focal point, thus producing a sharp image.
Barrel Distortion
Image distortion produced when the position of the camera lens is at its widest angle. Lines you expect to appear perpendicular are not. It is most noticeable when you have a straight edge near the side of the frame, such as when taking a wide angle shot of a building. Barrel distortion causes the edges of an image to look curved or at a skewed angle. Most barrel distortion can be corrected using image editing software.
Bracketing
Best explained as the photographer taking numerous photos of the same thing using a variety of different camera settings. Bracketing is great when you are struggling to get a shot with exposure you like and that suits the image generally and helps ensure correct exposure of a photo when lighting in a scene is difficult.
Camera Shake
Caused by even a slight movement of the camera as it records an image. Camera shake is the main cause of blurred images.
CCD Charge-coupled device
An image sensor that reads the charges built up on the sensor's photosites a row at a time.
Chromatic aberration
The inability of a lens to bring all light wavelengths (particularly red & blue) into the same plane of focus, thus causing overall blur. Usually found in regular large-aperture telephoto and super-telephoto lenses. Not improved by reducing aperture size. Can be corrected with low dispersion (ED, LD SD) glass.
CMYK
The four process colors used in printing: cyan, magenta, yellow, and black. CMYK image A four-channel image containing a cyan, magenta, yellow, and black channel. A CMYK image is generally used to print a color separation. When submitting photos to traditional printing presses you will often need to convert to CMYK. The conversion from RGB to CMYK will often cause dramatic changes in your digital image.
Color temperature - Color of Light
A method of expressing the color content and quality of light and measured in Kelvin (K). “Photographic daylight" has a color temperature of about 5500K. Photographic tungsten lights have color temperatures of 3200K to 3400K depending on their construction.
Depth of Field
Refers to how much of a photo is in focus when the camera is focused on the main subject. Depth-of-field is controlled by a camera's aperture, in conjunction with the focal length of the lens. Deep (more) depth-of-field means that all or most of the picture is in focus from front to back. Shallow (less) depth-of-field means that a subject is in focus but objects in front and behind it appear out of focus. Depth of Field
Digital Zoom
This is a common term for small video cameras and digital cameras. Digital zoom is electronic zoom where the camera interpolates the sensor readings to simulate a zoom.. Many people consider this to be a poorer quality image. Also see Optical Zoom
Electronic flash
Designed to provide light where the lighting on the scene is insufficient. Electronic flash requires high voltage, usually obtained through batteries and a voltage-multiplying circuit which discharge a brief, intensive burst. Generally considered to have the same photographic effect as daylight. Modern flash units have multiple TTL exposure control functions and auto focus control.
EXIF Data
Exchangeable Image File - Data that is stored in jpeg and TIFF image files, such as shutter speed, date and time, focal length, exposure compensation, metering pattern and if a flash was used a the time a photo was taken. EXIF data is very use when you are evaluating your photography.
Exposure Compensation
Increase or decrease the exposure an image from the exposure automatically selected by a camera metering system (see bracketing).
Exposure meter: Built-in digital camera meter that measures the amount of light when framing a photo and determines the best exposure. Matrix (Evaluative), Spot and Center-weighted are the main metering types; some digital cameras have all three.
F-numbers or F-stops
Numbers on the lens aperture ring and the camera's LCD (where applicable) that indicate the size of lens aperture. The lower the number the larger the aperture. As the scale rises, each number is multiplied by a factor of 1.4. Standard numbers are 1.0,1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc., each change resulting in a doubling or halving of the amount of light transmitted by the lens to the film. The actual value is represents a relationship between the focal length of the lens. f numbers are calculated by dividing the focal length of the lens by the effective diameter of the aperture.
Film Speed/ISO/ASA
ISO stands for International Standards Organization and numbers such as ISO 100 or ISO 400 etc. Film was always manufactured to be at a certain ASA. Digital cameras give you the ability adjust your sensitivyt to light or ISO. The higher the number, the more sensitive or faster the film. Basically, the slower the film (low ISO No.) the sharper and clearer the photograph. Grainy effects can be achieved with fast films (high ISO No.).
In a digital camera a higher ISO setting will mean the sensor is more sensitive to light and can allow faster shutter speeds. The negative side to this is that higher ISOs sometimes produce images that are noisy with digital grain.
Flash sync speed
Most modern cameras have two shutter panels, a top and a bottom one. When you press the shutter button, the top one starts to raise, and then the bottom one starts to follow, till the both meet and light is shut out. The speed you set your shutter will determine the time between when the top door starts moving and the bottom door follows (your camera make/model also can affect this).
Your max sync speed is essentially the setting at which the top door has reached the top of the sensor before the bottom door has started moving. It provides an entirely unobstructed view of the sensor for the flash to come in. A flash's duration is around 1/4000 or higher, so it will always be fast enough to hit the sensor for only a fraction of your shutter duration.
Your camera has a maximum "sync speed" at which time the panels are separated. However, some flash units have special modes which allow you to go beyond the "sync speed"
Focal Length
The distance from the film to the optical center of the lens when the lens is focused on infinity. Focal length on most adjustable cameras is marked in millimeters on the lens mount. On 35mm-format cameras, lenses with a focal length of 50mm are called normal or standard lenses. Lenses of 35mm or less are called wide angle lenses and lenses of 85mm or more are called telephoto lenses. Lenses which allow varying focal lengths without changing focus are called zoom lenses.
Focal Plane Shutter
A focal plane shutter exposes the image by moving two light-blocking curtains across the front of the image sensor. The first curtain slides open to begin the exposure, then the second curtain slide closed to terminate the exposure. In order to expose the picture from a flash, both curtains must be open at the time the flash is fired.
High Contrast
A wide range of density in a print or negative.
Highlights
The brightest areas of a subject and the corresponding areas in a negative, a print, or a slide.
Hot Shoe
The fitting on a camera that holds a small portable flash. It has an electrical contact that aligns with the contact on the flash unit's "foot" and fires the flash when you press the shutter release. This direct flash-to-camera contact eliminates the need for a PC cord.
Hyperfocal Distance
Distance of the nearest object in a scene that is acceptably sharp when the lens is focused on infinity.
KELVIN
The visible light spectrum is scientifically described in terms of color temperature, and is measured in degrees Kelvin (K). The temperature (usually measured in kelvin (K)) at which the heated black-body radiator matches the color of the light source is that source's color temperature; for a black body source, it is directly related to Planck's law and Wien's displacement law.
Lens
One or more pieces of optical glass or similar material designed to collect and transfer rays of light to form a sharp image on film, paper or a projection screen. In practical photography, compound lenses made of a number of elements of different types of glass are used. This enables the manufacturer to correct most of the faults (aberrations) found in simple lenses and provide images that are sharp across the whole picture.
Lens Speed
The largest aperture(smallest F-stop) at which a lens can be set. Fast lenses transmit more light and have larger openings than slow lenses. Determined by the maximum aperture in relation to focal length. Lens speed is relative: a 400 mm lens with a maximum aperture of F/3.5 is considered extremely fast, while a 28mm F/3.5 lens is considered to be quite slow.
Optical Zoom
A true zoom. The focal length of the lens extends and retracts so an image is magnified by the lens itself. Whatever the focal length of the lens, image resolution stays the same. Optical zooms produce the best photo quality (see digital zoom).
Overexposure:
Improper exposure causing an image to look too light. There is a loss of detail in bright areas.
PictBridge:
Aa standardized technology that lets you print images from a memory card in a digital camera directly to a printer regardless of brand. No computer is necessary.
Panning
This refers to following a subject with your camera. If you are photographing a runner you would want to follow the runner with the camera. Done correctly, your subject will be in focus and the background will show motion. This adds motion to a photograph.
Perspective
Perspective is a two-dimensional representation of a three-dimensional scene. In photography this can be achieved by viewing 3-D objects from an angle rather than head-on. A photograph is also given perspective if there are objects in the foreground, middle distance and background, giving the whole scene “depth". For most photographers perspective refers to the relationship of the subject to the camera sensor or film plane.
Prime Lens
A lens that has one focal length. For example 135 mm lens is a prime lens.
RGB
An additive color model that starts with black, the absence of light. Computer monitors emit a combination of three colors: red, green, and blue to create a full color display.
Saturation:
The intensity, or vividness, of a color. Increasing saturation makes colors in photos look richer. The amount of saturation can be adjusted in some cameras. It can also be increased or decreased with image editing software.
Shutter Lag:
The delay that takes place between pressing the shutter-release button and the time a photo is actually taken. Shutter lag times vary from digital camera to digital camera. Often the less expensive the camera the longer the lag.
Shutter Speed
The shutter speed is the length of time that the light capture medium is open to the light. 1/30 is 1/30 of a second. Try to keep your shutter speed 1/90 - 1/125 or faster to avoid camera blur. Anything less than 1/60 and you will need to either use a tripod or be very aware of your camera movement. It all depends upon you. For some, 1/60 may be too slow a shutter speed while others can work at 1/25th. Also note that the longer the focal length, telephoto vs wide angle lens, the more camera movement will affect image sharpness.
To obtain a blur effect on running water a slow shutter speed is needed. Depending on the amount of flow, 1/15 - 5 seconds is usually sufficient. To do this successfully it is necessary to use a tripod to eliminate camera shake.
If you wish to obtain a crisp image of a moving object then you will need a fast shutter speed of at least 1/250 or higher. (See Panning)
Single-Lens-Reflex (SLR) Camera
Light entering the camera through the lens is reflected up by a mirror behind the lens onto a ground glass screen above. This screen is viewed through the viewfinder and a glass pentaprism which turns the image the correct way up. Other camera functions such as light metering and flash control also operate through the camera lens.
Underexposure
A condition in which too little light reaches the film or camera sensor. In general digital handles underexposure better than negative film. Underexposed film will producing a thin negative, a dark slide, or a muddy-looking print.
Unipod or Monopod
A one-legged support used to hold the camera steady.
Vignetting
A fall-off in brightness at the edges of an image, slide, or print. This can be caused by poor lens design, using a incorrect lens hood, or attaching too many filters to the front of the lens.
Wide-Angle Lens
A lens that has a shorter focal length and a wider field of view (includes more subject area) than a normal lens.
Zoom Lens
A lens which can be adjusted to a wide range of focal lengths. This allows a photographer to carry fewer lens. Zoom lens are difficult to design and manufacture.
BASIC PHOTOGRAPHIC TECHNIQUES
Today, photography is
characterized by a rapid growth in the development of technology and ideas.
Each year, millions of pictures are taken and an astonishing array of new
films, cameras and imaging systems enter the market. One of the great
attractions of the photography field is the ease with which basic skills can be
learned.
Unlike some of the older
arts that take years of training to produce an acceptable product, anyone can
quickly learn how to take a picture; however, photographic techniques must be
mastered before you can become an accomplished photographer; therefore, mastery
of the basic fundamentals is the foundation upon which you will build your
photographic and professional skills as a Navy Photographer’s Mate. The
photographic techniques presented in this chapter are essential in producing
quality photographs, and you can apply each of these fundamentals, to some
extent, each time you take a picture.
All the following links would take you to http://photoinf.com for further information on photography.
Thanks to http://photoinf.com
Lesson
1: Photographic Composition, Center of
interest, Subject placement, Simplicity, Viewpoint and camera angle, Balance.
Lesson 2: Shapes and lines.
Lesson 3: Pattern, Volume, Lighting, Texture, Tone.
Lesson 4: Contrast, Framing, Foreground, Background.
Lesson 5: Perspective.
Lesson 6: Basic lighting techniques: Outdoor and Existing light photography.
Lesson 7: Composition and Basic shots or sequences.
Appendix: Subject and Rule of Thirds.
Lesson 2: Shapes and lines.
Lesson 3: Pattern, Volume, Lighting, Texture, Tone.
Lesson 4: Contrast, Framing, Foreground, Background.
Lesson 5: Perspective.
Lesson 6: Basic lighting techniques: Outdoor and Existing light photography.
Lesson 7: Composition and Basic shots or sequences.
Appendix: Subject and Rule of Thirds.
PHOTOGRAPHIC COMPOSITION
Photographic composition
is the pleasing arrangement of subject matter elements within
thepicture area. Creative photography depends foremost on the
photographer's ability to see as the camera sees because a photograph does not
reproduce a scene quite the way we see it. The camera sees and records only a
small isolated part of the larger scene, reduces it to only two dimensions,
frames it, and freezes it. It does not discriminate as we do. When we look at a
scene we selectively see only the important elements and more
or less ignore the rest. A camera, on the other hand, sees all the details
within the field of view. This is the reason some of our pictures are often
disappointing. Backgrounds may be cluttered with objects we do not remember,
our subjects are smaller in the frame or less striking than we recall, or the
entire scene may lack significance and life.
Good pictures are seldom
created by chance. To make the most of any subject, you must understand the basic
principles of composition. The way you arrange the elements of a scene within a
picture, catch the viewer’s attention, please the eye, or make a clear
statement are all qualities of good composition. By developing photographic
composition skills, you can produce photographs that suggest movement, life,
depth, shape, and form, recreating the impact of the original scene.
How are photographic
composition skills developed? You look, you study, you practice. Every time you
take a picture, look all around within the viewfinder. Consider the way each
element will be recorded and how it relates to the overall composition. You
must become thoroughly familiar with the camera and learn how the operation of
each control alters the image. Experiment with the camera and look at the
results carefully to see if they meet your expectations. With experience and
knowledge of your equipment, you begin to "think through your camera"
so you are free to concentrate on composition. Devote serious study to the principles
of good composition. Study books and magazine articles on composition. You
should analyze various media: motion pictures, TV, magazines, books and
newspapers, and evaluate what you see. What is good about this picture or that
TV image? What is bad about it? What principles of good composition could you
apply in a different way to make the picture better.
Good or correct
composition is impossible to define precisely. There are no hard-and-fast rules
to follow that ensure good composition in every photograph. There are only the
principles and elements that provide a means of achieving pleasing composition
when applied properly. Some of these principles and elements are as follows:
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As
you study these principles of composition, you should soon come to a
realization that some are very similar and overlap one another a great deal.
Because all or most of
these principles must be considered and applied each time you take a picture,
it may all seem quite confusing at first. With experience you can develop a
sense of composition, and your consideration and application of the principles will
become almost second nature. This is not to suggest that you can allow yourself
to become complacent or careless in the application of the principles of
composition. Doing so will be immediately obvious because the results you
produce will be snapshots, not professional photographs.
The
principles of composition that follow apply equally to both still and motion
media photography.
CENTER OF INTEREST
Each picture should have
only one principal idea, topic, or center of interest to which
the viewer's eyes are attracted. Subordinate elements within the picture must
support and focus attention on the principal feature so it alone is emphasized.
A picture without a
dominant center of interest or one with more than one dominant center of
interest is puzzling to a viewer. Subsequently, the viewer becomes confused and
wonders what the picture is all about. When the picture has one, and only one,
dominant "point of interest," the viewer quickly understands the
picture.
NOTE:
"Point of
interest," as used here, has the same meaning as center of interest;
however, using the term point of interest prevents giving the
impression that the center of interest should be located in the center of the
picture.
The specific topic,
idea, or object to be portrayed must be set in your mind as you prepare to take
a picture. When there is nothing in the picture to attract attention to a
particular area or object, the eyes wander throughout the scene. The center of
interest may be a single object or numerous ones arranged so attention is
directed to one definite area
When the center of
interest is a single object that fills most of the picture area or one that
stands out boldly, such as a white sail against a background of dark water,
attention is attracted immediately to it. As may be expected, not all subjects
are as simple to arrange or as bold and impressive.
A photographer usually
has at his or her disposal many factors or elements that can be used and
arranged within the picture area to draw or direct attention to the primary idea
of the picture. Some of these elements are lines, shapes, human figures, tone,
and texture.
Human figures attract
attention more strongly than almost any other subject matter and unless they
are the main object of the photograph should probably be kept out of the
picture; for instance, a photograph showing a person standing at some distance
in front of a building may leave the observer wondering whether the person or
the building is the primary subject. When people are included in a scene for
comparative size of objects or just for atmosphere, keep them from looking
directly at the camera. When people look at the camera and therefore at the
viewer of the picture, the viewer tends to return their gaze by looking
directly back into their eyes. When they are not the intended point of
interest, we miss the statement and purpose of the picture. When people are
subordinate elements within the picture and they are looking in a direction
other than at the camera, the viewer’s attention is directed from the people to
what they are looking at, which should be the
center of interest; for example, when people are grouped around a piece of
machinery that is the center of interest of the picture, have them look at the
machine, rather than the camera.
SUBJECT PLACEMENT
Sometimes good composition is
obtained by placing the center of interest in the geometrical center of the
picture; it is generally not a good idea to place it there. Too frequently it
divides the picture into equal halves and makes the picture uninteresting and
difficult to balance. By dividing the picture area into thirds, both
vertically and horizontally, and locating the center of interest at one of
the intersections of the imaginary lines, you can usually create a feeling of
balance to the composition (fig. 5-5).
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In photographic composition there are two
general guides for determining the best location for the center of interest. The first
is the principle of thirds. The other is dynamic
symmetry. In the principle of thirds, the intersection of lines that
divide the picture area into thirds are marked by O’s. These intersections
are good locations for the center of interest in most photographs. Notice we
said THE center of interest. Remember, have only one center of interest to a
picture-keep it simple. The principle of dynamic symmetry is a similar idea.
A good location for the center of interest is found by drawing or imagining a
diagonal line from one corner to an opposite corner. Then, draw a second line
perpendicular to the first from a third corner (fig. 5-6). The intersections
of the lines are the location for the center of interest.
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SIMPLICITY
Simplicity is the key to
most good pictures. The simpler and more direct a picture is, the clearer and
stronger is the resulting statement. There are several things to be considered
when we discuss simplicity. First, select a subject that lends itself to a
simple arrangement; for example, instead of photographing an entire area that
would confuse the viewer, frame in on some important element within the area.
Second, select different viewpoints or camera angles. Move around the scene or
object being photographed. View the scene through the camera viewfinder. Look
at the foreground and background. Try high and low angles as well as normal
eye-level viewpoints. Evaluate each view and angle. Only after considering all
possibilities should you take the picture. See beyond and in front of your
subject. Be sure there is nothing in the background to distract the viewer's
attention from the main point of the picture. Likewise, check to see there is
nothing objectional in the foreground to block the entrance of the human eye
into the picture.
A last point of
simplicity-tell only one story. Ensure there is only enough
material in the picture to convey one single idea. Although each picture is
composed of numerous small parts and contributing elements, none should attract
more of the viewer's attention than the primary object of the picture. The
primary object is the reason the picture is being made in the first place;
therefore, all other elements should merely support and emphasize the main
object. Do not allow the scene to be cluttered with confusing elements and
lines that detract from the primary point of the picture. Select a viewpoint
that eliminates distractions so the principal subject is readily recognized.
When numerous lines or shapes are competing for interest with the subject, it
is difficult to recognize the primary object or determine why the picture was
made.
VIEWPOINT AND CAMERA ANGLE
The proper viewpoint or
camera angle is an important factor in good composition. Repositioning your
subject within the viewfinder frame and changing the camera viewpoint or camera
angle are two simple ways of controlling composition.
Photographing from a
different viewpoint or camera angle can often add drama and excitement or even
bring out an unusual aspect of a subject. Most of the subjects you photograph
are three-dimensional and should be photographed from an angle (to the right or
left of and/or from higher or lower than the subject) that allows the viewer to
see more than one side of the subject. The photographer should study the
subject from different sides and angles. Walk around the subject and look at it
from all viewpoints. See it from elevated and low positions as well as from eye
level to find the best composition. This greatly assists in composing the
subject for the best balance and helps to select a background that compliments,
not distracts from the subject.
The terms viewpoint and camera
angle are often used in conjunction with one another and sometimes
used interchangeably. They can also have different meanings depending on how
they are applied. Viewpoint" is the camera position in relationship to the
subject. "Camera angle" is the angle in which the camera lens is
tilted; for example, a picture of sailors marching, made from ground level with
the camera held horizontal with reference to the ground, may be referred to as
a "low viewpoint" (or camera position); however, when this picture is
made, again from ground level, but with the camera pointed up, it may be
referred to as a "low camera angle." Likewise, a picture made from an
elevated or high position, with the camera again held horizontal with reference
to the ground, or even pointed straight down, can be referred to as a
"high viewpoint"; however, if the camera is not held horizontal to
the ground or pointed straight down, but pointed at some angle between horizontal
and vertical, the camera position could be referred to as a "high camera
angle."
Eye-Level Shots
With the camera held
horizontal, eye-level shots are usualIy made at a height of about 5 1/2 feet,
the height from which the average adult sees, and with the camera horizontal.
With the camera held at eye level but pointed up or down, the camera position
changes and you have either a low or high camera angle, respectively.
Low Viewpoint and Low Camera Angle
Low viewpoints and low camera angles
can add emphasis and interest to many ordinary photographs. A low viewpoint
can be used to distort scale or add strength to a picture or to emphasize
certain elements within the picture. A low camera angle is achieved when the
camera angle is located below the point of primary interest and pointed
upward. Low angles tend to lend strength and dominance to a subject and
dramatize the subject. Low angle shots are used when dramatic impact is
desired. This type of shot is very useful for separating the subject from the
background, for eliminating unwanted foreground and background, and for
creating the illusion of greater size and speed (fig. 5-7).
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High Viewpoint and High Camera Angle
High viewpoints
and high camera angles help orient the viewer, because they show
relationships among all elements within the picture area and produce a
psychological effect by minimizing the apparent strength or size of the
subject (fig. 5-8).
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Courtesy: http://photoinf.com
http://vimeo.com/41174743What is Focal Length, anyway?
What is F-Stop, anyway?
F-stop is the focal length divided by the diameter of the lens. For example, a 200mm f/4 lens will be 50mm wide. Get out your ruler and measure it. 200mm/50mm = f/4. That is why f-stop is typically written as F/4, meaning "focal-length over 4" or "focal-length divided by four".
Where do those numbers come from?
Lenses are marked with a series of f-stops, each one lets in half as much light as the previous one. The light-gathering ability of a lens is determined by its area, and f-stops are determined by diameter. Area is related to diameter squared. The progression of f-stops, 1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32, are powers of the square root of 2.
For a further explanation of f-stops, try this.
Taking the nature photographs like those in my books about Rocky Mountain National Park, Wildflowers and Wildlife require an assortment of lenses depending on the subject. Typically normal to wide angle lenses are used for landscape photos and very long telephotos are used for wildlife. The photographs below show the views of a single scene taken using these lenses.These eight photos were taken from the same place with different lenses. The subject is Longs Peak from Upper Beaver Meadows in Rocky Mountain National Park.
 | 24mm |  | 35mm |
 | 50mm |  | 100mm |
 | 200mm |  | 400mm |
 | 800mm |  | 1200mm |
"I want to take a bluebird picture. What lens should I use?" It is a symptom of bird photography that your lenses never seem to be long enough. This is because birds are so small. When photographing large animals, a 400mm gives you decent image size from a reasonable distance. But remember, an elk is six or seven feet tall. A bird is barely six inches long, so when your subject is twelve times smaller, you have to be twelve times closer. 
As you can see, even a relatively huge 600mm lens at the relatively close distance of 20 feet doesn't give the huge magnification you might expect. The field of view is about twelve inches. It takes a big lens to photograph a small bird.Courtesy:
http://www.paragon-press.com/lens/lenchart.htm
Refer the following link also
http://electronics.howstuffworks.com/cameras-photography/tips/10-important-photography-terms.htm#page=11
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