Depth of field: Correct use of sharpness and blur

Have you ever looked at someone’s eyes when bright light suddenly hits them? The pupils quickly become much smaller, a reaction that’s keeps too much light from entering the eye. In our camera, it’s the diaphragm or aperture that closes down to limit the amount of light. Control of the aperture opening means more than just adjusting light amounts. It also has a close relationship with something called depth of field. This refers to the area in front and back of the subject that is in focus at the some time as your subject. Along with the kind of lens and positions o the subject, the aperture you select has a definite bearing on whether the depth of field is great (a lot of the picture in focus) or shallow ) only the subject and immediate area in focus).

When a lens focuses on a subject at a distance, all subjects at that distance are sharply focused. Subjects that are not at the same distance are out of focus and theoretically are not sharp. However, since human eyes cannot distinguish very small degree of unsharpness, some subjects that are in front of and behind the sharply focused subjects can still appear sharp. The zone of acceptable sharpness is referred to as the depth of field. To be technically correct, DOF is the zone of acceptable sharpness, the area in front of, and behind, a focused subject that appears in focus. Thus, increasing the depth of field increases the sharpness of an image. We can use smaller apertures for increasing the depth of field.

Depth of field is the range of distance within the subject that is acceptably sharp. The depth of field varies depending on camera type, aperture and focusing distance.

The depth of field does not abruptly change from sharp to unsharp, but instead occurs as a gradual transition. In fact, everything immediately in front of or in back of the focusing distance begins to lose sharpness-- even if this is not perceived by our eyes or by the resolution of the camera.

What we really want to know as photographers is what affects depth of field so we can control depth of field in our pictures. For a long time, photographers have gone with the following three criteria:

• lens aperture
• distance from subject
• focal length

Lens Aperture

The aperture is simply the size of the opening that allows light to go through the lens. It is expressed in f/stops (also referred to as f/value or aperture value), and a typical aperture range is f/2.8 - f/8, giving the range from maximum (large at f/2.8) to minimum (small at f/8) aperture. A small f/value (e.g. f/2.8) indicates a large aperture. For instances if we use an aperture of f/2, we may be surprised to find that although we have focused on the subject properly, not much else is very clear. That’s because large aperture sizes equal shallow depth of field. If possible, changing to a smaller aperture and corresponding slower shutter speed is advisable if we want some of the background in focus.

Distance from subject

When we focus on a subject close to the camera, the DOF is less than when you focus on the subject farther away from the camera. We can also control depth of field b y changing distance from the subject. Even with the same aperture and distance, the depth of field effect will be different. Step away from our subject to obtain greater depth of field, or move in closer to decrease depth of field.

Focal Length

A wide-angle lens has greater depth of field than a telephoto lens. Most consumer digital cameras have very short focal lengths and that is why it is so difficult to obtain shallow depth of filed , even with the aperture opened up wide. In another case even with the same aperture and distance the depth of field gets shallower the longer the focal length of the lens.

Digital Photography

From photojournalism to family photos, digital photography is still photography.
Digital photography has become very popular because the digital camera has made photography very easy, accurate and convenient. With the ease of picking up a digital camera and getting a useable photograph, it is still important to learn how to use a digital camera and how to change the settings on the camera to get the best digital photography results. Regardless of camera type, the photograph is ultimately the most important thing.
Good photography is always about recognizing and responding to the subject, not about the computer. That means shooting the right way from the start, no matter what camera you use. Many things about digital cameras are identical to film cameras, a few things are slightly tweaked from film expectations, and a number of features are unique to digital photography. Some of the big differences can actually help you take better pictures than you ever did with a film camera.
For quality results from any camera, the basics of photography still apply no matter how an image is captured. A tripod is always important if slow shutter speeds are needed and big telephoto lenses are used. Fast shutter speeds remain a key way to stop action, and f-stops continue to affect depth of field. The important parts of a scene still need to have the focus centered on them, and dramatic light always helps make for dramatic photos.
• Get close. Check out your lens. See what it can do by stepping in closer and placing something in the foreground. What happens to the background? Is it fuzzy or sharp?
• Shoot a lot of pictures. Remember, it's digital, so you can!
• Low light will increase digital grain. Use a flash or other added light if grain could be a problem and must be kept to a minimum.
• Being perfectly still is the first step to making better pictures.
• The most common mistake people make is camera shake. When you move the camera inadvertently at the time you press the shutter, you risk the chance of blurring your image or reducing the sharpness of the image.
• A different vantage point can be refreshing when photographing kids and animals.
• White balance is more than a colour correction tool. Use it creatively to get the colors you want in your scene.
• The sensor sensitivity (commonly referred to as ISO) is simply a measure of the sensor's sensitivity to light. If you are setting the ISO manually, here is a basic guide: 100 ISO in bright, bright sunlight; 400 ISO on a dull, dreary day; 800 or 1600 ISO for indoors under floodlights; generally speaking, the higher the ISO, the lower the picture quality.
• Black-and-white photography has many possibilities with digital cameras. A scene can be shot directly in black and white with the camera or it can be captured in colour and later changed in the digital darkroom.
• Adjust your resolution selector to the “High” position for best results.
• To get accurate and sharp results from digital photography, you should click the photograph from as close as possible. If this is not possible, you should use the zoom feature that brings the subject closer to the camera.
• The red-eye reduction feature should be used with your flash if individuals are to be photographed in order to avoid the individual’s eyes turning red in the photograph.
• Consider taking the photograph from a different angle than just straight ahead.
• Always keep spare batteries with you, especially when you are traveling.
• Try to have one or two extra memory cards with you if you are going for a long trip.
• Digital cameras have a review feature that can show you the result of the picture that you have just taken. If you find that it is not up to your expectations, all that you have to do is to erase the one that you do not want and click another one.

THEORIES OF VISUAL COMMUNICATION

• Sensual Theories
• Perceptual Theories
Sensual Theories
• Gestalt
• Constructivism
• Ecological
Gestalt
• Proposed by Max Wertheimer, a German psychologist.
• Gestalt means form or shape.
• The whole is different from the sum of its part.
• The eye merely takes in all the visual stimuli and that the brain arranges the sensation into coherent images.
• Visual perception was a result of organizing sensual elements or forms into various groups.
• Four laws of grouping
– Similarity
– Proximity
– Continuation
– Common fate

Muller-Lyer Illusion

• Criticized for describing perceptions rather than explaining how perceptions give meaning.

Constructivism
• Julian Hochberg, psychology prof. (Columbia Uni.), 1970, found that human eyes constantly in motion as they scan an image.
• The viewer constructs the scene with short-lived eyes fixation, the mind combines into a whole picture.
• Help to explain how mind perceive difficult image
• Important for explaining diffficult object
• A minor clarification of Gestalt theory

• Mario Garcia and Pegie Stark used Eye-Trac testing machine found that content, size and placement of photos are more important than whether the image is colour or black & white.
• Emphasizes the viewer’s movement in an active state of perception.

Ecological
• Founded by James J. Gibson, Prof. Of Psychology at Cornell Uni.
• The approach states that:
– The study of visual perceptions should involve subjects in the natural surrounding
– Isn’t simply a combination of images scanned by eyes fixation (constructivism), but is a product of the way light affects the appearance of the objects within a field of view.
• Ambient optical array (AOA)– visible surface structures
– Slight changes in AOA, need no conscious mental calculations – automatically process perceptions.
• Criticized for lack of explanation on the entire process of human perception.
• Human perception of visual images, is a cognitive process, involves many factors – previous experience, cultural factors, and linguistic abilities.

Perceptual Theories
• Semiotics
• Cognitive

Semiotics
• Study/science of signs
• Developed by two philosophers;
– Ferdinand de Saussure
– Charles Sanders Peirce
• Signs is simply anything that stands for something else.
• 3 types of signs – iconic, indexical, symbolic.
• Images are collections signs
• 3 types of signs – iconic, indexical, symbolic.
– Iconic – some form similarity between signs and object it represents.
– Indexical – complex meaning, smoke represent house on fire, physical causation.
– Symbolic – an arbitrary convention, culture, belief, etc.

• Roland Barthes, describe codes (chain of association), signs that make up picture narratives.
– Society develops complex system of codes.
• Metonymic code – a collection of signs that cause viewer to make assumptions/associations
• Analogic code – cause viewer to make mental comparison
• Displaced code – transfer meaning from one set of signs to another.
• Condensed code – several signs combined to form new, composite signs, particularly images used outside the culture.
– Semiotics emphasize the importance of symbolism in the visual perception and communication.
Cognitive
• Viewer does not simply witness a light-structured object, but actively arrives at a conclusion through mental operations.
• Visual perceptions are affected/determined by several mental activities (Carolyn Bloomer):
– Memory, projection, expectation, selectivity, habituation, salience, dissonance, culture and words.
• Human mind is an infinitely complex living organism that science may never fully understand.

Time line – history of photography.

• ancient times: camera obscuras used to form images on walls in darkened rooms; image formation via a pinhole
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• Leonardo da Vinci, using his house as a so called camera obsura and improving the image with a lens, invited some friends to have a look.
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• 16th century: brightness and clarity of camera obscuras improved by enlarging the hole inserting a telescope lens
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• 1727: Professor J. Schulze mixes chalk, nitric acid, and silver in a flask; notices darkening on side of flask exposed to sunlight. Accidental creation of the first photosensitive compound.
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• 1800: Thomas Wedgwood makes "sun pictures" by placing opaque objects on leather treated with silver nitrate; resulting images deteriorated rapidly, however, if displayed under light stronger than from candles.
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• 1816: Nicéphore Niépce combines the camera obscura with photosensitive paper
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• 1826: Niépce creates a permanent image
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• 1834: Henry Fox Talbot creates permanent (negative) images using paper soaked in silver chloride and fixed with a salt solution. Talbot created positive images by contact printing onto another sheet of paper.
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• 1837: Louis Daguerre creates images on silver-plated copper, coated with silver iodide and "developed" with warmed mercury; Daguerre is awarded a state pension by the French government in exchange for publication of methods and the rights by other French citizens to use the Daguerreotype process.
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• The invention of the daguerreotype process was announced by the Frenchman Louis Daguerre in 1839 and was widely acclaimed. The image produced had a startling clarity and made the daguerreotype hugely popular as a medium for portraiture until the middle of the 1850’s. To create a daguerreotype, a silver plated sheet was given a light sensitive surface coating of iodine vapour. After a long exposure in the camera, the image was developed over heated mercury and fixed in a solution of common salt. As the image lies on the surface of a highly polished plate, it is best seen from an angle to minimise reflections.
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• 1841: Talbot patents his process under the name "calotype".
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• William Henry Fox Talbot patented the Calotype process in 1841. It is the direct ancestor of modern photography because it used a negative permitting multiple positive prints to be made from the negative and development of the latent image. The negative was a sheet of high quality writing paper which had been made light-sensitive with chemicals. Because the image was contained in the fabric of the paper rather than on a surface coating, the paper fibres tended to show through in the prints making them mottled and relatively ‘sketchy’.

• The collotype process was used between about 1870 and 1920. A glass plate was coated with sensitised gelatin and exposed under a negative. Light passed through the negative would harden the gelatin on the glass plate. The unexposed gelatin would absorb the water when washed and the exposed would repel it. The washed glass plate would be coated with ink, adhering to the exposed gelatin and printed onto fine paper.
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• 1871: Richard Leach Maddox, an English doctor, proposes the use of an emulsion of gelatin and silver bromide on a glass plate, the "dry plate" process. Gelatin silver prints are the most usual means of making black and white prints from negatives. They are papers coated with a layer of gelatin which contains light sensitive silver salts. They were developed in the 1870's and by 1895 had generally replaced albumen prints because they were more stable, did not turn yellow and were simpler to produce. Gelatin silver prints remain the standard black and white print type.
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• The albumen print was invented in 1850 and was the most common type of print for the next 40 years. It produced a clearer image than its predecessor, the salted paper print. An albumen print was made by coating paper with a layer of egg white and salt to create a smooth surface. The paper was then coated with a layer of silver nitrate. The salt and silver nitrate combined to form light sensitive silver salts. This double coated paper could then be placed in contact with a negative and exposed to the sun to produce a print
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• 1878: Dry plates being manufactured commercially.
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• 1880: George Eastman, age 24, sets up Eastman Dry Plate Company in Rochester, New York. First half-tone photograph appears in a daily newspaper, the New York Graphic.
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• 1888: first Kodak camera, containing a 20-foot roll of paper, enough for 100 2.5-inch diameter circular pictures.
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• 1889: Improved Kodak camera with roll of film instead of paper
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• 1900: Kodak Brownie box roll-film camera introduced.
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• 1906: Availability of panchromatic black and white film and therefore high quality colour separation color photography.
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• 1907: first commercial color film, the Autochrome plates, manufactured by Lumiere brothers in France
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• 1914: Oscar Barnack, employed by German microscope manufacturer Leitz, develops camera using the modern 24x36mm frame and sprocket 35mm movie film.
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• 1917: Nippon Kogaku K.K., which will eventually become Nikon, established in Tokyo.
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• 1924: Leitz markets a derivative of Barnack's camera commercially as the "Leica", the first high quality 35mm camera.
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• 1931: development of strobe photography by Harold ("Doc") Edgerton at MIT
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• 1932: On March 14, George Eastman, aged 77, writes suicide note--"My work is done. Why wait?"--and shoots himself.
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• 1934: Fuji Photo Film founded. By 1938, Fuji is making cameras and lenses in addition to film.
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• 1936: development of Kodachrome, the first color multi-layered color film; development of Exakta, pioneering 35mm single-lens reflex (SLR) camera
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• World War II:
o development of multi-layer color negative films
o Margaret Bourke-White, Robert Capa, Carl Mydans, and W. Eugene Smith cover the war for LIFE magazine
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• 1947: Henri Cartier-Bresson, Robert Capa, and David Seymour start the photographer-owned Magnum picture agency
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• 1963: first color instant film developed by Polaroid; Instamatic released by Kodak; first purpose-built underwater introduced, the Nikonos
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• 1980: Elsa Dorfman begins making portraits with the 20x24" Polaroid. An instant film, giving an almost immediate positive print.
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• 1982: Sony demonstrates Mavica "still video" camera
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• 1983: Kodak introduces disk camera, using an 8x11mm frame (the same as in the Minox spy camera)
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• 1985: Minolta markets the world's first autofocus SLR system (called "Maxxum" in the US)
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• 1992: Kodak introduces PhotoCD