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BASIC PHOTOGRAPHY

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					                                            BASICS IN DENTAL PHOTOGRAPHY

DEFINITION:
          Photography is the process of making pictures by means of the action of light.
           Light reflected from an object forms a picture on a material sensitive to light. This picture is then chemically processed
into a photograph; which provides a representation of the object.
          The word photography comes from Greek word meaning “to write or draw with light”
          Photography has been in existence for over a century. It can best be described as an „Art‟ for various purposes. It can be
a hobby, a profession or a science as it has developed into in recent years. The use of photography are emence. It varies from a
family snap shots which is a reminder of our past days, arial photographs to learn about enemy loop movements and plan battle
strategy. Anthropologists and sociologists study photographs of various groups of people for clues to patterns of human
behaviour.
HISTORY :
          The ancient Greek Philosopher Aristotle observed that light passing through a small hole in the wall of a room framed on
dawn image of an object. However this character of light was not used until about AD 1500. In Italy the first crude camera,
called a „camera obscure‟ (Dark chamber) was made. It consisted of a huge base with a tiny opening in one side that admitted
light and on the opposite side, the light formed an inverted image of the scene outside. The hole was soon replaced with a lens
which made the image brighter and sharper, which artists used as sketching aid. But this could only project images onto a screen
as a piece of paper.
          In 1727, a German physicist named Johann H.Schulye discovered that silver salts turn dark when exposed to light.
About 50 years later Carl Scheeje, a Swedish chemist, showed that the changes caused in the salts by light could be made
permanent by chemical treatment.
          In 1826, a Frenchman, Joseph N.N. coated a metal plate with a light sensitive chemical and then exposed to plate in the
camera obscura for about 8 hours. The resulting picture, showing the view from Joseph‟s window was the world‟s first
photograph. In 1830‟s Louis Daguerre, a French man, exposed a sheet of silver coated copper, developed the image with mercury
vapour, and „fixed‟ it with table salt. His pictures called „Daguerreatyper‟ required a relatively short exposure time 15 to 30
seconds and produced sharp and detailed images.
          In 1839, a Britisher, W.H.Fox Talbot invented a light sensitive paper which produced a negative from which positive
prints could be made. His friend, an astronomer Sir John Herschel suggested the use of sodium thiosulphate (Hypo) as a fixing
agent, and called the invention „Photography‟. In 1840‟s Joseph M.Petyral, attungarian mathematician designed two types of
lenses, one for making portraits and other for landscape pictures.
          In 1851, a British Photographer, Fredrick S.Archer coated a glass plate with a mixture of silver salts and an emulsion
made of wet, sticky substance called “Colodion”. In 1871, Richard L.Maddox a British doctor, used an emulsion of gelatin to
coat photographic plates. IN 1888, George Eastman, an American dry plate manufacturer, introduced Kodak Box Camera which
was the best of that kind, designed specifically has mass production and amateur use. This camera has a roll of Gelatin coat ed
film that could record 100 “round photograph and developed in Eastmans processing plants. They made prints and returned the
camera loaded with a new roll of film. In 1924, Leic a Company introduced a 33 mm camera which was small enough to fit in a
pocket, but it produced clear, detailed photographs. The elective flash bulb introduced in 1929 and electronic flash bulb,
introduced in 1931, greatly expanded the range of photographic subjects. Color film was first commercially produced in 1935 and
was popular among amateur photographers since 1970‟s.
          Photography today is firmly established as both an art form and an essential tool in communication, research and a
greater variety of styles and themes than ever before.
Important Terms in Photography:
1) Angle of view: The particular portion of a scene that is covered by a camera lens. The area is determined by the focal length
     of the lens.
2) Aperture: Lens opening. The opening in a lens system through which light passes. The size of the aperture may be fixed or
     adjustable. Lens openings are usually calibrated in numbers.
3) Auto focus camera: Camera which adjusts the lens for correct focus on the subject automatically.
4) Back ground : The part of the scene that appears behind the main subject of the picture
5) Blow up : An enlargement; a print that is made bigger than the negative or slide.
6) Camera angles : Various positions of the camera (high, medium or straight) with respect to the subject, each giving a
     different view point as effect.
7) Candid pictures : Imposed pictures, often takes without the subjects knowledge.
8) Contrast : The density range of a negative, print or slide, the brightness range of a subject or the scene lighting.
9) Cropping : Using only part of the image that is in the negative or slide.
10) Density : The blackness of an area in a negative or print which determines the amount of light that will pass through it as
     reflected from it.
11) Double exposure : Two pictures taken on one frame of film or two images printed on one piece of photographic paper.
12) Emulsion : A thin coating of light sensitive material, usually silver halide in gelatin, in which the image is framed on film
     and photographic paper.
13) Exposure : The quantity of light allowed to act on a photographic material.
14) Film speed : The sensitivity of a given film to light. It is indicated by a number in ASA / ISO rating, the higher the number,
     the more sensitive or faster the film.
15) Over exposure : A condition in which too much light reaches the film, producing a dense negative as a washed out print.

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16) Panorama : A broad view, usually scenic.
17) Range finder : A device included on a camera as an aid in focusing.
18) Parallax : At close subject distance, the difference between the field of view seen through the view finder and the lens.
    There is no parallax with single lens reflex lens.
19) Reflex Cameras : A camera in which the scene to be photographed is reflected by a mirror onto a glass where it can be
    focused and composed. In a reflex movie camera as a single lens reflex camera (SLR), the scene is viewed through the same
    lens that takes pictures thus avoiding parallex, with a twin lens reflex camera (TLR) the scene is viewed through the top lens
    and the picture is taken through the bottom lens.
20) Shutter : Some movable cover in a camera which controls the time during which light reaches the film.
21) Zoom lens : A lens in which the focal length can be adjusted over a wide range.

                                                              CAMERA :
          A camera is basically a base, with a small aperture (opening) where the lens is attached at one end and film at other. The
inside of the camera must be completely dark, so that rays of light reach the film only through the aperture when a device called
shutter opens.
Principle :
          The camera works in much the same way as the eye. The lens in the eye focus the image on to the nerve cells in the
retina and this image is sent to the brain by the optic nerve. If a pencil is held in front of the eyes about 2 feet far and if viewed at
it the objects farther away will appear out of focus. If looked beyond the pencil to the far end of the room, it immediately cames
into a focus and the pencil is blurred. It is because, the muscles of the eyes are acting on the lens adjusting it, so that the image,
which is looked at, is sharply focussed onto the back of the eyes.
          This is the same principle employed in the camera. The lens sharply focuses the image on the film. To keep the image
sharp even when the distance varies, the lens has to be moved either closer or farther away from the film, in the same way as the
iris of the human eye contracts to the bright sunlight but opens when the person is in a dark room.
          Light reflects from an object and enters the camera through the lens, which focuses the rays of light into an image on the
film. Light rays from the top of the subject form the lower part of the image and those from the bottom form the upper part. Thus
the image on the film is upside down.
Types of Camera :
          Nearly all cameras have the same basic design, which includes an aperture, a shutter, a view finder and a film advance.
But the cameras differ in features such as adjustability and type of film used. The simplest camera is called fixed focus cameras
and has a non-adjustable lens and majority of them uses 110 sized film. Professional cameras, including view cameras and studio
cameras, have many adjustable parts and uses large sheets of films.


1) Sheet Film Cameras :
         The sheet film camera is the most basic form of apparatus. It composed of flat panels; the front one supports the lens,
shutter and aperture, and the back one holds a ground glass screen for focussing.

         The image of a photographer standing behind a large camera with a black cloth covering his head, may today seem
archive and irrelevant, but is not so. These cameras are still in use and for color images used in poster advertising, sheet film
cameras are essential.

2) 35 mm Non Reflex Cameras :
They are mainly of two types ;
a) Snap shot cameras
b) Range finder cameras

a) Snap shot cameras : Majority are totally automatic, all functions of these cameras takes place with out photographers
   intervention – apart from pressing of shutter release.
b) Range finder cameras : Most camera functions are set manually though there may be automatic exposure system. However
   the most obvious difference is in the view finder which is mechanically coupled with the cameras focusing mechanism.

3) Cartridge and Disc Cameras :
        They are direct decedents of the worlds‟ first cameras.
a) Disc Cameras : They are usually used by beginners who do not wish to learn any more. They are extremely simple to load
    and operate and produce acceptable results. Each frame of film measures less than a square centimeter.
b) Cartridge load cameras : These have a fixed focus lens that forms sharp pictures of subjects two meter away or more. Usually
    they are available in 2 types : 110 and 126 sizes. These cameras accept cartridges of films of respective sizes.

4) Instant Picture Cameras :
          These are quite bulky because the film itself must be the same size as the final picture. The principle of operation is the
same. Film is loaded into the camera in a small light tight pack, containing ten sheets. It is pushed into the camera and when the
shutter release is pressed, a small motor ejects an opaque cover sheet. Now the camera is ready to take pictures and the motor
ejects pictures after exposure. The time taken will be only 10 seconds for black and white and 60 seconds for colour prints.


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5) Twin Lens Reflex Cameras (TLR) :
         These cameras have their viewing lens directly above the picture taking lens. The image in the viewing lens is reflected
onto a screen at the top of the camera. A person hold the camera at his waist or chest or above the head and looks at the viewing
screen. The viewing screen is much large and clearer. The negative format is 5.7 cm and this enables reasonable enlargement to
be made without undue worry about grain or loss of definition. However these cameras are subject to parallax error, and are
heavier, and most TLR cameras donot have interchangeable lenses.

6) Single Lens Reflex Cameras (SLR) :
         This camera enables a photographer to look at a subject directly through the lens. A mirror mechanism between the lens
and the film reflects the image onto a viewing screen. When the shutter releases, the mirror rises out of the way, so that the light
exposes the film. Thus the photographer sees the image almost exactly as it is recorded on the film and parallax error is avoided.
Most of these cameras uses 35 mm film and are heavier and more expensive. The standard lens can be replaced by lenses that can
change the size and depth relationship as objects in a scene.

Special Cameras :
         There are some times special photographic problems that cannot be solved using any general purpose camera. Coping
with these special problems there are certain highly specialized type of cameras.
a) Panoramic cameras : These cameras uses an ultrawide angle lens which will have a broader field view.
b) Under water cameras : These are also called amphibeam cameras which are specially made water proof.
c) Sterographic cameras : These cameras have twin optical system to make two pictures simultaneously. Here the printing is
    done on a special prismatic photographic paper, which makes a 3D effect for the viewer.
d) Aerial Cameras : These cameras are specially made for using from an aircraft where the focus is fixed on infinity.

ELECTRONIC CAMERAS :
          Just as video tapes store moving images, so magnetic tapers or discs can store still images – so called video floppies.
Lenses :
          The lens is the heart of the camera. It is the component that turns the three dimensional world outside the camera into
two dimensional image on the film. To some extent the quality of the lens determines the quality of the photograph. The lenses
used with most cameras today are very complex. The principle of all cameras is same as that of a magnifying lenses that gathers
light of the sun to burn a hole in a piece of paper.

         The bending of light on entering a different transparent medium is called refraction, the bending power of that medium is
called the refracture index.

           A lens is like a series of prisms, which are stacked up together. The prisms in the center o the lens have parallel sides and
closer to the edge of the lens the prisms have steeper and steeper angles. The light passing near the center of the lens is only bent a
little but the light passing away from the center of the light is bent more. So parallel light passing through the lens all converge on
the same point called the focus of the lens.

Covering Power of a Lens :
         All the lenses form circular images, with the sharpest part of the image in the middle and dimmer and more blurred
towards the edges. The point of which the image falls below an acceptable standard represents the covering power of the lens.

         In photography the film format must fit within this circle. On a camera the covering power is increased slightly by
stopping down the aperture i.e. smaller. IN 35 mm film one frame is 24 x 36 mm and the frame diagonal is 43 mm. So lenses for
35 mm cameras must form sharp images at least 43 mm in diameter.

Focal Length and Magnification :
          Focal length is the distance from the film to the lens to get a sharp image of an object. However for complex camera
lenses this definition is not of much practical use, because the lens barrel holds the glass elements in the right place in relation to
the film and it controls how much the image of the subject is magnified. Lenses with higher focal lengths will form magnified
images, but show a more restricted field of view where as lenses with lower focal length will give a broader field but smaller
images of the subjects. Shorter focal lenses are called wide angel lenses. Lenses with F.L. longer of standard lenses are usually
called as telephoto lenses.

Types of Lenses :

1) Standard Lenses :
          These are lenses that show the subject roughly as the human eye does. It is usually well corrected and gives sharp and
clear images and has got maximum aperture. For 35 mm cameras, 50 mm is the standard lenses and usually has aperture from F
1.4 to F 32.

2) Wide Angle Lenses :
         These lenses have focal length less than the film diagonal. It gives a broad field of view. But background of the picture
appears farther away. This will have greater depth of field. For 35 mm camera, 35 mm lens is ideal for a crowd.

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3) Fish Eye Lenses :
         These are extreme wide angle lenses in which no attempt has been made to prevent straight lines from bowing. Eg. 8
mm lens.

4) Telephoto Lenses :
          These lenses form magnified images of the subject, or permit the photographer to fill the frame with the subject from a
distant view point. For 35 mm camera, telephoto lenses have focal length between 85 and 2000 mm. These are commonly used in
sports and wild life photography.

5) Zoom Lenses :
         These lenses have got variable focal lengths. Turning or sliding a ring on the lens barrel makes the subject larger or
smaller in the view finder. This allows the photographer to capture the picture very precisely and frame the subjects perf ectly.
For 35 mm cameras, the most successful lens are of focal length range from 50 mm upto about 210 mm. Typical lenses run from
80-200 mm or 75-150 mm.

Special Lenses :
1) Night lenses : They are ultrafast standard lenses having aperture of F 1.2 or exceptionally F1. These lenses make
    photography possible at very low light levels.
2) Shift lenses : (Perspective control lenses) : these are wide angle lenses which move up, down and sideways relative to the
    film. This enables, for instance, buildings to be photographed without converging vertical.
3) Macro Lenses : Specially made for photographing small subjects. Mechanically a macro lens has a specially long focussing
    range, so that the lens can focus continuously from infinity down to eight inches or so.
4) Medical lenses : They are similar to macro lens but have built in ring flash.



                                                              Shutter :
         The earliest cameras had no shutter. They did not need them because they were using very slow light sensitive materials
and the exposure lasted for several minutes, even in bright sunlight.

         Modern photographic films are more sensitive and faster and the speed of the shutters has kept in pace with the speed of
the films.

        The purpose of a shutter is to protect the film from light until the chosen moment and then to open has a precisely
measured time before closing once more. Shutter speed is the amount of time the shutter remains open during exposure. Shutters
have range of speed from ½ seconds to 1/8000 seconds or even more.

Shutters of two types ;
1) Leaf shutter : it is usually built into the lens with which it is to be used and consists of a number of thin metal plates.
2) Focal plane shutters : This type of shutters is housed in the camera just infront of the film. These type are very essential in
   SLR Cameras because the reflex viewing requires an open lens. It offers high speed upto 1/8000 of a second with faster
   shutter speed we can „freeze‟ the motion of speeding object and with slower shutter speed we can blur the image of the same.

                                                             Aperture :
         Aperture is a hole through which the light passes from the subject to the film. Together with the shutter the aperture
controls the light which reaches the film.
         Small aperture let through little light but render most of the subject sharply. Large apertures let through more light but
record only shallow plane clearly.
         The size of the aperture is controlled by device called diaphragm, which consists of a circle of overlapping metal leaves.
The diaphragm expands to make the aperture larger and contract to make it smaller.

        The various sizes of aperture are called „F‟ stops or „F‟ numbers. The „F‟ stopes can start from 14 and can go upto 32.
These numbers refers the measure of the size of the lens but not the diameter of the aperture.

        It is the number by which the focal length of the lens must be divided to yield the aperture diameter. For example, a 50
mm lens is set to F2 aperture, the diameter of the aperture is 50/2 i.e. 25 mm. Where F stands for focal length of the lens.

          Lower the number the larger the aperture size and higher the number smaller the aperture. Changes in the size of the
aperture affect the overall sharpness of the picture. As the aperture becomes smaller the area of sharpness infront of and behind
the subject becomes larger. The area of sharpens is called “Depth of the field”. It extends from the nearest part of the subject area
in focus to the farthest part in focus. So a small aperture such as F/11 or F/16, creates greatest depth of the field. If the aperture is
opened by F/4 or F/2 the subject will be in focus but objects in the „fore ground‟ and background may be blurred.

         The matching progression of shutter speed and aperture size makes settings of the two controls very easy and convenient.

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                                                               EXPOSURE :
         Is the total amount of light that reaches the film in a camera (i.e. intensity of the light X time). Exposure affects the
quality of photographs more than any other factors. If too much light enter the camera, the film will be over exposed and the
picture will be too bright and if there is insufficient light, the film will be under exposed, resulting in dark uninteresting picture.

       Proper exposure for a picture depends chiefly on ;
1) The lighting
2) The subject
3) The desired depth of the field

         Each of these factors may require an adjustment in the shutter speed or aperture size. The amount of light in a scene
affects both shutter speed and aperture size. On a cloudy day, the shutter speed should be reduced and increase F/stop. On a
sunny day the shutter speed should be increased and the aperture should be small.

         The type of subject to be photographed may require an adjustment in the shutter speed and the depth of field may
determine the aperture size. If the subject is moving the shutter speed should be increased to prevent blurring. If a large area of
the picture is to be brought in sharp focus a small aperture should be chosen to provide greater depth of field.

         A fast shutter speed stops the action, but it also reduces the amount of light reaching the film. To make up for this
reduction of light the aperture size should be increased. Similarly small aperture reduces the amount of light, hence a slower
shutter speed should be selected.

         Most modern cameras have built in exposure meters that measure the light reaching the film.

                                                          FILM :
       There are 3 main kinds of photographic films based on the type of pictures produced. They are ;
1) Black and white
2) Colour
3) Colour reversal film



Black and White Films :
         It is used to get black and white prints. It is composed of 6 layers. A scratch resistant coating protects the emulsion
layer, which contains silver halide crystals suspended in gelatin. These crystals react with light to form photographic image. An
adhesive substance binds the emulsion to a plastic film base. A second adhesive layer attaches the film base to an antihalation
coating which prevents internal reflection.

Colour Film :
          It is used to obtain colour prints. Colour film tripack takes its name from its three emulsion layers, which contains dyes
sensitive to blue, green and red light. A filter is included to protect the green and red dyes from interfering with yellow light. The
top of the pack is protected by scratch resistant gelatin coating, a second glelatin coating, containing an antihalation substance,
which protects the underside. This coating is bonded to plastic film base. When the film is developed the images retained by the
separate emulsion layers combine to produce a colour photograph.

Colour Reversal Film : (Colour Slides) :
          Closely resemble negative films in their composition. The only difference is that the couples in slide films are colourless,
while those in the negative films are coloured. The processing of transparency film is more complex than that of a negative film,
as extra stages are needed to turn the negative back to a positive.

Other Films : Instant Films
1) Black and white instant films – peel apart films which makes a black and white picture, and like all instant films it relies on
   the diffusion of the image from one part of the film to other. The negative sheet which is exposed to light carries fairly
   conventional light sensitive emulsion. The other sheet, which is not light sensitive, is a piece of specially coated paper. This
   receives the image after the 2 sheets are laminated together by putting through metal squeeze rollers. These rollers burst a
   pad of viscous chemicals, which develop the image on a similar image diffusion principle.
2) Instant colour : This also works on a similar image diffusion principle.
3) Single sheet films : Principles same as that of a peel apart colour films.
4) Instant transparencies : Here the image forming emulsion on the film is of same type and the development takes place in a
   special processor.

Special Films :
        Black & white and colour infrared films. It has got an infrared layer, which will give a false colour to an object.
        The most important characteristics of the film includes ;

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1)   Speed
2)   Graininess
3)   Colour sensitivity
4)   Colour balance

Speed :
          Speed is the amount of time required for the film to react to light. The speed of the film determines how much exposure
is needed to record an image of the subject. A fast film reacts quickly to light and needs little exposure. This type of film can be
used for scenes that have dim light or involve fast action. A medium speed film requires moderate exposure and is suitable for
average conditions of light and movement. A slow film needs much exposure and should be used for stationary subjects in a
brightly lighted scene.

          The principle systems of measuring films speed are the DIN system i.e. German Industrial System. ASA which is
American Standards Association and ISO stands for International Standards Organization. The higher the ISO/ASA numbers, the
faster the speed of the film. Films that have numbers 200 and higher are generally considered fast. Medium speed films have
numbers ranging from 80 to 125 and slow film are numbered lower than 80.

Graininess :
         It is the speckled appearance of some photographs. It is caused by clumps of silver grains on the film. The degree of
graininess depends upon the speed of the film. A fast film is more sensitive to light than other films because its emulsion contains
larger grains of silver salts and it produce little or no graininess in standard size prints, though some grains may appear in
enlargements in the case of medium films.

Colour Balance :
         It applies only to colour films. Such film is sensitive to all colours, including those of different kind of light. The human
eye sees light from nearly all sources as white. However colour film records lights from ordinary light bulbs as reddish, light from
fluorescent bulb as blue green and day light as slightly blue. Variations in emulsions of different types of colour film mak es the
film less sensitive to certain colours. These variations balance the colour of light recorded on the film so that colours in the
photograph appear natural. Most colour film is balanced either for day light or for specific types of artificial light.

FOCUSING :
       Focusing controls the sharpness of the image in a photograph. The degree of sharpness is determined by ;
1) The distance between the camera lens and the subject.
2) The distance between the lens and the film inside the camera.

         To form a sharp image of a subject which is close to the camera, the lens must be relatively far from the film. For
subjects far from the camera, the lens must be close to the film.

         Since the film is a flat plane behind the lens, the parts of the subject that are in focus form a flat plane infront of the lens.
This plane is called the plane of sharp focus and it is usually at right angles to the axis of the lens.

         On cameras which have adjustable lenses, the lens moves in and out in a threaded barrel and allows precise setting of the
lens film separation. The barrel can be marked with widely spaced indexes to indicate the correct position of the lens for different
subject distances. This focussing scale runs from infinite distance through to a distance of a meter as 2 from the camera.

         In the case of sheet film cameras, the rear of the camera is a sheet of malt glass, on which the lens throws an image of the
object. The photographs can then move the lens in and out watching the change in the sharpness of the image on the screen.

         In case of twin lens reflex cameras (in TLR‟s) there are 2 identical lenses, one above the other. The lower one forms
image on the film where as the upper one forms image on the viewing glass. The lenses are linked rigidly together, and more in
and out on the same panel for focusing. This ensures that the image on the film and focusing screen are focused on the same part.
But, since both lenses are separated by several centimeters, the viewing lens doesnot see, precisely that will appear on the film.

DENTAL PHOTOGRAPHY :
          As dentists we live in a time when complete and comprehensive documentation of our therapy is essential. The aim of
dental photography is to record a maximum of information under conditions, which should be as reproducible as possible.
Photographs for comparison over time can be obtained only if the conditions under which they are taken are reproducible. The
photographic equipment used, the framing of the picture, the scale of reproduction and lighting are constant. If all these
conditions are standardized it is possible to take intra oral and extra oral photographs, which allows direct comparisons, even if
their tacking is separated by long periods of time and different photographs have been responsible.

TOOLS :
Camera :



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         The types of cameras that can be used for clinical photography include, orthoscan camera, Polaroid cameras, 35 mm,
single lens reflex with 100 mm macro or 100-150 mm, short manual lenses on automatic bulbs and single or twin lens reflex
cameras, which uses 120 film and 150 to 180 mm lenses.

           The earliest intraoral camera to use is the orthoscan camera. It produces a 1:1 ratio in a properly oriented perspective
(right is right, left is left) of full upper or full lower arches on Polaroid film only. Polaroid type 107 film yields a 15 second black
and white print. Polaroid 105 film prints a black and white print in 60 seconds, plus a black and white negative which has to be
cleared in sodium sulfite solution, washed and dried. Polaroid 108 film produces a colour print in 60 seconds.

         The main advantages of this type of camera are the convenience of seeing the result within a few seconds, ease of
operation and compact design.

        But the lenses of these cameras are not of highest quality with an exception of Polaroid 195 series to a certain extent.
Photographs from these cameras usually give distorted images thus limiting their practical use for dental documentation.

          The twin lens reflex cameras can cause parallax error in close working conditions as focusing and viewing are done using
different lenses, which are at different heights.

         The most suitable and frequently used clinical camera for dental photographs is the 35 mm single lens reflex camera. It
has advantages over view finder cameras for there is a problem of parallax in close working conditions and both the focus and
depth of field can be observed visually on the viewing screen. Cameras, which use larger films are more complicated, are more
expensive and are of no special advantage in dental photography.

         The most critical item of equipment is the lens. The characteristics of the lens determines whether a camera can be used
for dental photography.
         Two parameters of particular importance are determined by the types of lens employed.
         They are ;
1) The scale of reproduction
2) The clear working distance

         The scale of reproduction is the ratio of image size to subject size. The clear working distance is the distance from the
subject to the front surface of the lens.

         For dental photographic purposes maximum scales of reproduction of 1:1 or 2:1 are required. The scale of reproduction
together with the focal length of the lens determine the clear working distance.

         Focal length in the range of 100-135 mm have proved most suitable. Ideally 100 mm or 105 mm for 35 mm cameras
provides, the least perspective. Shorter focal lengths do not allow a sufficient clear working distance. If this is too short there may
be hygiene problems. More over the subject may also be incorrectly illuminated and be reproduced with a perspective not
corresponding to normal perception. Too short focal lengths will make subjects close to the lens over-emphasized. For example,
if a model of jaw or a natural row of teeth is photographed with a standard lens of insufficient focal length, the anterior teeth will
be rendered disproportionately large.

Lighting :
         Standard conditions should also be aimed at the choice of the light source and the direction of the lighting. The best light
has dental photography is provided by an electronic flash. Constant lighting in the form of photofloods should be used for portrait
photography only.

Lateral Flash :
        The simplest and most common arrangement is lateral mounting of the flash unit. This results in high contrast pictures
obtained with a minimum of technical complexity. But for taking intra-oral photographs a lateral flash source can create
problems. If the working distance is too short, the illumination will be uneven. For this reason, when lateral flash is used the clear
working distance should be long enough and the flash unit should be rotatable to a position directly beside the lens.

Ring Flash :
        Ring flash is extremely popular especially in intra-oral photography. The flash reflection takes the form of a ring
surrounding the lens. Hence the light axis and the optical axis of the camera coincides, giving a shadowless illumination.

          The advantages of ring flash lighting are that even highly inaccessible areas are well and uniformly illuminated. Ring
flash permits uniform illumination even at large scales of magnification and with short object distances. The disadvantages of
ring flash illumination is that the photographs lacks modeling, i.e. they do not clearly show surface texture.

Double Lateral Flash :
        A combination of two laterally positioned flash sources gives evenly illuminated pictures, which also show some degree
of modeling. The colour structure of teeth is reproduced better with lateral illumination than with axial lighting from a ring flash.

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Another advantage of the double lateral flash configuration is that by varying the direction of the axis of the individual flash units,
it is easier to adapt to the surface of the particular subject and to illustrate the particular point the picture is to convey.

          To sum up, it can be said that in dental photography lateral flash, preferably double gives better illumination than in ring
flash but the ring flash finds its justification in intra oral photography where in-accessible areas have to be illuminated. Ring flash
again has an upper hand when persons with little experience of photography have to take the pictures as is often the case in routine
clinical practice.

       To conclude the recommended principal standard components of an outfit suitable for all aspects of dental photography
are ;
1) 35 mm single lens reflex camera.
2) Macrolens of 100 – 135 mm focal length, allowing reproduction on a scale of 1:1 or preferably 2:1.
3) Lateral flash : Single or preferably double, ring flash can also be used for intra oral photography.

Necessary Tools :
         In addition to photographic equipment, suitable photographic mirrors as well as lip retractors are essential for production
of high quality intraoral photographs.

Intraoral Mirrors :
         For good photographs with out double images, surface coated glass mirrors are required. The rhodium – coated
photographic mirrors are suitable for intra oral photography. Intra oral mirrors with long handles are preferable as they will be
easy to handle.

         Fogging of intra oral mirror due to patients‟ breath is a problem faced during intra oral photography. It can be solved by
any of the following methods.
1) The patient can be asked to breath through the nose.
2) Blow air on the mirror using an air way syringe.
3) Application of anti-efflorescence.
4) Immersion of the mirror in warm water for few minutes prior to insertion.

A variety of lip and cheek retractors are needed to project the best possible light on teeth and to isolate relevant objects.
Retractors made of clear plastic are most suitable as they can be easily modified and are most comfortable for the patient.

PHOTOGRAPHIC METHODS :
Extra Oral Photography (Portraits and Profile Photographs) :
       Generally 6 views are included in E.O. photography. They are ;
       Left and right lateral views, the frontal view, the frontal view with head inclined back wards and two fronto-lateral views.


          All pictures are taken with the camera in the vertical position and at the patients‟ eye level. Particular importance
attaches to the choice and positioning of the background and of the lighting.

Background :
         The background should be such that it does not interfere with assessment of the profile. It should be unstructured and
non-reflective. Felt or cardboard are very suitable materials. Dental instruments or other materials should not be included in the
picture. A grey background is best for general purposes. It does not cause exposure problems or influence the colour rendering.
Coloured backgrounds may also be suitable.

Illumination :
         Photofloods or electronic flash illumination may be used. The arrangement of the lighting should be as simple as
possible. A single light source is sufficient for all portraits and profile views. The lighting direction and the distance of its source
from the background must be chosen so that the shadow of the head falls outside the field of view of the camera. The light should
always come from the profile side. This gives good modeling of the angle of the mandible and the ramus.

Position of the Mandible :
         The six standard views are all taken with the mandible in the rest position i.e. the patient is relaxed with the lips resting
and in normal relation.
         In certain clinical situations photograph may have to be taken with teeth closed or in lateral excursion to the left or right.
Thus for each of the six standard views, there are four variations in the position of the mandible.
1) In the rest position
2) In occlusion
3) In lateral excursion to the left
4) In lateral excursion to the right

Lateral Views :

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         Lateral views are necessary to assess the profile. The following arrangements should be observed for lateral views:
         1) The top edge of the frame should be just above the crown of the head and the bottom edge in the region of the larynx.
The empty area of the frame should be positioned in the front of the profile. The camera should be focused on the patients‟ eye.
The head should be aligned so that the Frankfort plane is parallel to the top / bottom edge of the picture. The ear should not be
covered by hair. For correct reproduction of the profile, the force should be turned 3-5o towards the camera. This position
compensates for the illusion in a straight profile that the head is turned away from the lens. As a rule of thumb the mesial outline
of the eyebrow turned towards the camera should be visible.

          When consistent head position is not reproduced, distortion of appearance is likely. A backward head tilt will give a
prognathic appearance, particularly in the profile view. A forward head tilt will give a retrognathic appearance. Head rotation
alters the appearance of symmetry in frontal view.

FRONTAL VIEW :
         This view of the face can reveal and record asymmetries. Frontal light should be avoided as this gives flat illumination
and may result in ugly „red eye‟. Lateral light from one side casts a shadow on the side away from the light, which hampers
assessment of symmetry. IT is therefore necessary to brighten the side of the face away from the light with a reflector. This will
give an even illumination with good modeling. This can be done using two lateral light sources.

         The top edge of the frame should be just above the crown of the head and the bottom edge in the region of the larynx.
The camera is again focused on the patients eye. The head should be aligned so that the bipupillary line is parallel to the upper /
lower edge of the frame. The distance from the outer canthus of the eye to the hairline should be equal on each sides. The line
from the outer canthus of the eye to the superior attachment of the ear should also be parallel. This line parallels the F.H. is a
consistent, practical and clinical anatomic reference.

Inclined Frontal View :
         A frontal view with the head inclined backwards by 45 o is commonly used in orthognathic cases and in plastic surgery,
particularly in patients with clefts of lips or palate or deformities of nasal septum.

          A lateral light source with reflector or two light sources to the left and right of the patient should be used. The top edge
of the frame is above the forehead and the bottom edge below the larynx. The camera should be focused on the nasal entrance of
the patient. The head should be aligned so that the bipupillary line is parallel to the top or bottom edge of the frame.

Fronto Lateral Views :
         In these views the sagittal plane is oriented about 45 o to the optical axis. This type of photograph is necessary in cases
before and after surgery.

          Illumination is by a lateral light source, which must always come from the side of the face to which the tip of the nose
points. This ensures that the patients shadow falls outside the field of view of the camera. The edges of the frame should be just
above the crown of the head and in the region of the larynx. The camera should be focused on the mesial contour of the eye
turned towards the camera. The F.H. plane should be parallel to the upper and lower edges of the frame. The head should be
turned away from the camera just sufficiently for the lateral contour of the orbit on the non camera side to be still completely
visible i.e. not masked by the eye ball.

Intra Oral Photography :
          Five standard intra-oral views together provide the complete oral photographic record.
They are ; Frontal views, the left and right lateral views of the teeth and the two occlusal views. Some of these views are taken
directly and some through photographic mirrors.

The Frontal View :
       For frontal view the following arrangements are appropriate.
1) The center of frame should be at the point of contact between the upper central incisors.
2) Centre of focus should be between canine and first premolar.
3) Edge of frame should be at the lateral edges beside the last molars.
4) The occlusal plane should be parallel to the upper or lower edge of the frame.

          The illumination used is provided by a lateral flash unit in the 12 O‟clock position, a double lateral flash combination or
a ring flash.

The Lateral Views :
       The lateral view is ideally taken as follows ;
1) The centre of frame should be at the tip of the second premolar.
2) Centre of focus should be also at the tip of the second premolar.
3) The edge of the frame should be beside the last molar or at the side of the central incisor.
4) Occlusal plane should be parallel to the upper or lower edge of the frame.


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         The lateral view can be also taken with the help of a mirror. A standard lip and cheek retractor and a narrow, elongated
mirror are needed. The dental assistant should place the mouth angle retractor into the mouth opposite the side to be photographed
with the mouth open, the narrow mirror should then be inserted into the vestibulum, and the patient should be asked to carefully
close the jaws. The mirror has to be held at an adequate distance from the buccal surface to enable all teeth from the molars to the
canine to be viewed.

The occlusal view of the mandible :
        This view should be taken as follows :
1) The centre of frame should be at the intersection of the sagittal plane with the line joining the second premolars.
2) Centre of focus should be in the sulcus or in the region of the marginal gingiva of the premolars
3) Edge of frame should be distal to the last molars and in front of the incisors.

          The retractors should be placed and occlusal mirror is inserted and the patient is requested to open his mouth as wide as
possible. The patient is asked to shift the tongue upto the palate, prior to insertion of the occlusal mirror. The tongue should be
shifted to prevent the tongue resting on the teeth. The mirror should be held at a distance from the mandibular teeth, to make as
full a view as possible.

The occlusal view of the maxilla :
        This view should be taken as follows ;
1) The centre of frame should be at the intersection of the sagittal plane with the line joining the second premolars.
2) The centre of focus should be in the sulcus or on the marginal gingiva of the premolars.
3) The edge of the frame should be behind the molars and in front of the incisors.

         These five pictures provide an overall view of the dental arches. The scale of reproduction used should be between 1:1.5
and 1:1.8.
         If more details are required, pictures of groups of teeth can be taken. Here again, the use of fixed conditions will provide
comparable pictures. For groups of teeth it is not possible to stipulate precise conditions, for the requirements to be satisfied by
such pictures are too variable. However a few general rules should be observed if uniform photographs are to be obtained.
1) Photograph the teeth in correct axial alignment. This means that the occlusal plane should be parallel to the horizontal in the
    picture.
2) Try to align the optical axis perpendicular to the row of teeth to be photographed. This will give consistent views and reduce
    the depth of field problem.
3) When mirrors are used photograph only mirror images.
4) Every unwanted thing that might distract the attention of the observer should be avoided as far as possible.




CONCLUSION :
         Concluding a seminar on photography is probably a difficult proposition. The reason for this lies in the vastness of this
field which makes a discussion on photography seem like a small island in this big ocean.
         Yes, we have to evolve from the basics of photography and progress towards the other finer details involved in this
endeavour.
         No matter how much effort a photographer puts in to produce the best photographs, if this photograph is not processed
properly, then all the efforts are in vain as we may land up with a poor outcome. Therefore the processing plays an important role
in photography and its role in the same cannot be overemphasized.

        In our department call it a boon or a blessing, but all of us have definitely been lucky enough to handle such sophisticated
photographic equipment for which we should be thankful to our professor.

         What really matters is or it boils down to a single point – are we really taking photography seriously. The answer is
„Yes‟, because of the very fact of me standing infront of you and presenting a seminar on photography.

          So let me conclude with this saying.
          “What we think we know today, shatters the errors and blunders of yesterday and is tomorrow discarded as worthless. So
we go from larger mistakes to smaller mistakes, so long as we do not loose courage. This is true of all therapy; no method is
final” – Frederic Jensen.

         Photography is no exception to this rule. So this seminar is only about „basics in dental photography‟ there is a long way
ahead.




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