FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
SUBJECT FORENSIC SCIENCE
Paper No. and Title PAPER No.7: Criminalistics & Forensic Physics Module No and Title MODULE No.26: Basic Principles of Photography
Module Tag FSC_P7_M26
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
TABLE OF CONTENTS
1. Learning Outcomes
2. Introduction: Photography
3. History of Camera & Photography 4. Light
4.1. Sources of Light 4.2. Colour Temperature
5. Terminology used in Photography 5.1. Film
5.2. Film Speed 5.3. Exposure 5.4. Aperture 5.5. Depth of Field
5.6. Shutter & Shutter Speed 6. Types of Camera
6.1. Analog Camera 6.2. Digital Camera
7. Types of Analog Cameras (Film Camera) 7.1 View Camera
7.2 Point and Shoot Camera 7.3 Twin Reflex Camera 7.4 Single Reflex Camera
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
1. Learning Outcomes
After studying this module, you shall be able to
• Learn History of Camera & Photography
• Understand Basic Principles of Photography
• Understand Terminology used in Photography
• Learn about different Types of Camera
2. Introduction : Photography
The word “Photography” comes from the Greek word (Photos = Light, Graphos = Writing) meaning “Writing with Light”. The word camera is also derived from another Greek word “Kamara” – meaning anything within an arched cover or enclosure. A room is called „kamra‟ in Hindi. Photographic camera is a light tight box with light sensitive material (film) at one end and a lens or pin-hole (to admit light) on the other end.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
3. History of Camera & Photography
Mo-Tsu (China, approximately 500 B.C.) and Aristotle (Greece, 384 – 322 B.C.) observed the formation of inverted image when light passed through a pin-hole and both of them investigated independently.
At the beginning of the nineteenth century the first use of chemistry for Photography was done by Thomas Wedgwood ; he made negative by placing a drawing (on glass) on a paper previously treated with silver nitrate solution and finally exposing it to the sunlight. He also tried to record image with Camera Obscurabut in vain, as silver nitrate was not sensitive enough. His negative was not permanent.
William Henry Fox Talbot in 1835 independently produced a light sensitive paper by bathing it first in common salt and when dried, in silver nitrate, together the chemicals formed silver chloride. On this treated paper, he made contact prints of things like lace and leaves – what we called photogram today and the prints were fixed in common salt solution or with the solution of potassium iodide.
Talbot‟s photogram was, of course, negative but he soon evolved a method of reversing them to form positive by printing them on to a second sheet of sensitized paper. Sir John Herchel, (Talbot‟s friend) termed the first picture as negative and the reversed one as positive it is the fundamental principal of modern photography. By the advice of Sir Herchel, he adopted a more permanent way of fixing by using hypo-sulphite of soda to wash out unexposed silver halide.
A typical Camera Obscura at the beginning of the 19th century, somewhat larger than the replica shown above, incorporates a mirror which reflects the image from the lens onto a glass plate which holds a sheet of paper on which the image is being traced. The double interlocking box enables precise focusing of the image.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
By using potassium bromide instead of common salt he made more sensitive emulsion. In 1840 he modified the process, which was first called Calotype and later Talbotype.
In 1847 collodian (a protection for wounds) was discovered, it was used as a base by Archer in 1851, who exposed it in wet condition so it was called as Wet Collodian Process. Charles Bannet, in 1878, used gelatin to form dry plate and it was the true ancestor of film materials. In 1888 George Eastman first introduced Kodak Camera which was laden in factory and developed in the factory after exposure. In 1889 Eastman introduced to public the transparent celluloid film which could even be processed by the amateurs.
Even with the passage of time various developmental work continued on paper, films, photographic chemicals, lenses, cameras and other specialization related to the present day modern photography – even when the digital photography have been evolved surpassing the age old paper, film and chemical processes.
1826 – The first recorded heliography, looking out of the
window into the yard, was modified camera Obscura
(J N Niepce)
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
The first Kodak Camera with a celluloid film
Photograph has been described as „Printing with Light ‟. While a painter uses his brush to create a picture, a photographer uses his camera plus the fact that Silver Nitrate turns black on exposure to light.
The word „Camera‟ is derived from the Greek word „KAMARA‟ which means room. At the beginning it was a light proof room or tent with a hole fitted with a lens and was used by the painters to trace images by pencil on a canvas or a paper.
Later this principle was utilized to attain the principle of recording an image in a photographic camera. But to retain its past form, some of the different discoveries were utilized viz. 1614 Angelo Sola‟s finding of the property of Silver Nitrate turning dark when exposed to sunlight; Joseph Prieslay‟s (1772) comprehensive description of chemistry of light or chemicals in light and so on.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
The camera works in much the same way as our eyes. The lens in the eye focuses the image on the nerve cells in the retina at the back of the eye and this image is sent to the brain by the optic nerves. Let us take a simple example – hold a pencil in front of your eyes at about 2 feet distance. Objects away will appear out of focus. When you look beyond the pencil to the far end of the room, it immediately comes into focus, the pencil being blurred. The muscles of the eyes are acting on the lens, adjusting it so that the image we are looking at is sharply focused on the back of the eyes.
After that the ancestor of our Camera came and it is a light tight box with the following parts:-
i. A lens to produce an image.
ii. A fitting to hold a light sensitive film or plate.
iii. A focusing mechanism for subjects at different distance.
iv. Diaphragm: A metal sheet with hole kept in between the lens and photo- sensitive plate so as to control the intensity of light.
v. Shutter: A mechanical device by which the light entering through the lens is normally prevented from falling on the film but it can be displaced for a certain span of time by some button so as to pass the light for certain duration on the film for exposure.
vi. Viewfinder: It is a device to see the area being photographed. This is how we can know the area being covered by the lens.
Let us understand light before understanding the parts of a camera because photography is not possible without light:-
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
4. Light
Light is a form of energy which helps to see the objects in the material world around us, that is, it is the link between the eyes and the viewed objects.
Visible light waves are the only waves we can see from the complete spectrum of the electromagnetic waves. We see these light waves as the colors of the rainbow. Each color of the rainbow has a particular wavelength. Red has the longest wavelength and violet has the shortest wavelength among the seven colors of rainbow (VIBGYOR).
VIBGYOR is seen when the white light is split into its component colours when it passes through a prism, this phenomenon is known as dispersion.
In the atmosphere, the formation of rainbow can be seen at times when water vapors act as prism for the light that breaks apart wavelengths which creates a VIBGYOR. The colours are as mentioned below like Violet, Indigo, Blue, Green, Yellow, Orange and Red. Before violet there is an invisible ray called Ultra-Violet and after red the invisible ray is called Infra-Red rays. These invisible rays can also be detected by photographic plates/films.
A typical human eye can see light from 400 nm to 700 nm of the electromagnetic spectrum. This range is called visible range. Not all colours that human eyes can distinguish are in the visible spectrum such as brown, which is mix of multiple visible spectrum colours.
Although photography is possible even in non-visible range of electromagnetic spectrum such as in ultraviolet and infrared region, here we will only concentrate on photography in visible spectrum region.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
The wavelength of various colours of the visible spectrum is given in the table below, but we will discuss wavelength of each color, in detail, one by one.
Colour Wavelength(nm)
Red 622-780
Orange 597-622
Yellow 577-597
Green 492-577
Blue 455-492
Violet 390-455
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
4.1 Sources of Light
In photography, two types of light sources are used namely
Natural light Artificial light
Sun Tungsten Bulb
Starlight Fluorescent Lamp
Volcano
Electronic Flash Diya(Lamp)
LED Lamps
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Bioluminescence
Studio Probe
Candle Laser
From the chart, it becomes obvious that a natural light source comes from different sources of nature on which we do not have any control. Their availability and location is completely governed by nature. As a photographer one should only understand the characteristic of the natural light and how to use it in the best way.
On the other hand artificial lights are manmade lights which are sometimes completely under control and we have the freedom of choice how to use them either as a single source or in a mixed way. Most forms of commercial/advertising, forensic, scientific photography uses artificial light.
4.2 COLOUR TEMPERATURE
Colour Temperature can be explained as in simple terms as the colour an object produces under different light sources. That means various natural and artificial light sources produces different Colour temperature. This varies from red to blue. Candles, tungsten bulbs and sunsets gives light which is close to red color (hence they give „warm‟ look to the pictures), on the other hand clear blue skies gives a „cool‟ blue light.
Color temperature is generally recorded in Kelvin, which is the S.I. unit of absolute temperature.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Cool colors like blue and white usually have color temperatures above 7000K, on the other hand warmer colors like orange and red have color temperatures around the 2000K mark.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics
MODULE No.26 : Basic Principles of Photography
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Photographic films are sensitive to Colour temperature. There are daylight type and tungsten light type films available which gives natural Colour when exposed in respective light sources. In digital cameras however we can control the Colour temperature through White Balance setting and this will be discussed as we come to digital photography.
So, at different time of the day at different conditions we have different colours. Human eyes are so highly developed that they cannot see the change, on the other hand brain quickly adapts to the difference, but Colour films and recently the digital sensors cannot adapt. As mentioned before, Colour films can only be set to one Colour temperature, usually 5500°K which is the average Colour of a sunny day noon or 3200°K which is the temperature of a sunny daylight.
5. Terminology used in Photography
5.1 Films
The heart of the film is a transparent plastic material (celluloid) called the base. The back side of the film is generally shiny and has numerous coatings that are important for physical handling and processing of the film.
The other side of the film is the sensitive side where the photochemistry happens. There are 20 or more than 20 separate layers coated in the film that are mutually less than one thousandth of an inch thick. Most of this thickness is consumed by a very special binder called gelatin that grips the imaging components together.
Part of the layers which are coated on the transparent film don‟t form images. These layers which don‟t form images are present to filter light, and to control the chemical reaction which occurs in the corresponding steps. Sub-micron sized crystals of silver- halide are there in the imaging layer, that act as photon detectors.
These crystals are supposed to be the heart of the photographic film, as they undergo a photochemical reaction when exposed to various modes of electromagnetic radiations -- light.
Silver-halide grains are prepared by mixing silver-nitrate and halide salts (chloride, bromide and iodide) in complex ways which results in a range of crystal sizes, shapes and compositions. Then these undeveloped grains are chemically modified to increase their light sensitivity.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
To make these grains more sensitive towards blue, green and red light, organic molecules known as Spectral Sensitizers are added on the surface of the grains. These molecules adsorbs (attach) to the surface of the grain and transfers the energy from a red, green, or blue photon to the silver-halide crystal as a photo-electron. Some other chemicals are then added within the grains during its growth process, or added on the surface of the grain. These chemicals affect the light sensitivity of the grain, known as its photographic speed (ISO or ASA rating).
Generally there are three types of films:-
Black & White negative film Colour negative film Colour positive film (transparency)
5.2 Film SPEED
Film speed is a unit to express the sensitivity of the films towards light. That means how much amount of light is required by a particular film to give a standard exposure. More sensitive film takes fewer amounts of light and time to create an image in a particular lighting condition. The main units to express film speed are:
ASA – American Standard Association ISO – International Standard Organization DIN Deutsche Industries Norm.
Manufacturers all over the world usually make films as per Film Speed mentioned. Any brand of film purchased from anywhere in the world of a particular film speed will require the same amount of light to expose a particular subject in a particular light condition.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
More sensitive the film, less the amount of exposure is required for taking a photograph and vice versa. More sensitive the film or higher the film speed, the picture becomes more grainy and lower the film speed, sharper the picture.
Generally films are categorized as per their film speed as follows:- Film
Speed
12 25 50 100 200 400 800 1600 3200 Slow Speed Film Medium Speed
Film
High Speed Film
Ultra High Speed Film
The difference between slow and fast film is quality. Slow speed films usually produce sharper and more detailed image while faster films have higher contrast and grains.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Film Speed is very important while calculating exposure of a photograph or the power of an electronic flashgun. Earlier the camera exposure meter worked according to the film speed setting of the camera. Once a film of a particular speed is loaded in a camera, all the photographs are to be exposed calculating exposure according to that particular film speed. Today in digital photography we can change the film speed or the sensitivity of the sensor even for every frame just by pressing a button or a dial.
5.3 EXPOSURE
Exposure is the amount of light required to create a standard image on a photosensitive medium of a given sensitivity. Exposure is the combined effect of light falling on the photosensitive material i.e. the film and the sensitivity of the film (film speed).
The effect of the light falling on the film can be controlled by Aperture and Shutter Speed. The sensitivity of the film is another controlling factor for the exposure which is called Film Speed which has been explained in the last unit. So technically it is the joint calculation of intensity of light and its duration.
5.4 APERTURE
Aperture is an opening in between or at the back of a lens which controls the amount of light coming through it, it may be a fixed or variable.. Bigger the opening more the light and smaller the opening less the light falling on the sensitive material. This is one of the devices to control the exposure of the film or digital medium. It is expressed as “f”
number and every next bigger aperture gives double the amount of light.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Evaluation of the opening of the lens will vary the amount of light passing through the lens. If we increase the aperture or reduce the f-stop number, more light will pass through the lens. Every step towards higher F No: halves the light and every step towards smaller F No: i.e. bigger hole doubles the amount of light. So if we take a photo with a bigger aperture than required, more light will reach the photosensitive material and the photograph will become brighter than a standard exposed image and if it is smaller, it will become darker than normal.
Standard apertures are:-
f/64, f/32, f/22, f/16, f/11, f/8.0, f/5.6, f/4.0, f/2.8, f/2.0, f/1.8/f1.4
5.5 Depth of Field
One more thing that is intricately related to aperture is Depth of Field. Depth of Field refers to how much of the picture is in focus. When we focus the camera lens to give a sharp image of a particular subject, other objects closer or far away in the photo are going to be out of focus if they are at a different distance from the focused subject. The decline of the sharpness (for a particular „f‟ no.) of other objects is gradual. A shallow Depth of Field means that only the subject is in focus while everything else is out of focus. A Deep depth of Field means that everything is in focus. But for our practical purposes we select a zone in front of and behind the focused subject so that the blur in this zone is too small to be noticeable and can be accepted as sharp. This zone is called Depth of Field.
So, the aperture also controls how much of the photo is in focus. If the aperture is small then everything will be in focus, while a large aperture will make objects blurred, even slightly far from the subject.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Here we can see an example of a large aperture e.g. f/5.6, bringing little into focus, and a smaller aperture e.g. f/20, obtaining more Depth of Field.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
5.6 Shutter and Shutter Speed
This is a part of a Camera which blocks or restricts the light from entering the film plane and exposes the film. the mechanical or electromechanical system for controlling the time during which light is allowed to reach the light sensitive material in a camera i.e.
film or digital sensor is known as Shutter. It consists of some means of covering the image created by the lens, opening or uncovering for a pre-determined duration of time and covering it again. It can be activated by releasing the shutter release button. There are mainly two types of shutter, a) Diaphragm or Leaf Shutter & b) Focal Plane Shutter.
Diaphragm or Leaf Shutter was devised by Mr. Friedrich Deckel of Germany in 1912.
This type consists of 3 to 5 metal blades which can open outwards leaving a clear hole for exposure and covers again after a preset time. The speed is controlled by penions and leavers. This type is generally mounted in between the lens components.
William England in 1861 invented the Focal Plane Shutter. It consists of one or more roller blinds of fabric or metal, having a generally variable slit which moves across, inside back of the camera just before the film or the sensitive material when the release is pressed. It may move up & down or across from left to right or vice versa. When exposure time begins, the first curtain is released to start its travel.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
As it moves, the first curtain passes across the film frame, allowing light to fall on the film. When the first curtain has completed its travel, the frame is fully opened. When exposure time ends, the second curtain is released to begin its travel and close off light to the film.
Shutter Speed is the duration of time generally expressed in seconds, during which any type of shutter remains fully open for exposure. This excludes the opening and closing time which is considered to be negligible. Along with aperture, shutter speed indirectly controls the light falling on the sensitive material. The standard shutter speeds are 1/2000, 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1 sec.
So, here also every shutter speed mentioned provides half the amount or duration of light in relation to the speed to its right and double the amount or duration of light in relation to the speed to its left. That means a shutter speed of 1/60 gives half-light as compared to 1/30 and double as compared to 1/125.
Fast Shutter Speed Slow Shutter Speed
Object is freezed Object is blurred
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Therefore the correlation between shutter speed and aperture size is a direct one. Since, aperture and shutter speed both of them controls the amount of light reaching onto the film (let slip from mind about the elements of Depth of Field, action freezing or movement) And since both doubles and reduce in a scale of one time (1X or 100%): It means you can FREELY interchange the settings on shutter timing and lens opening for respective effects and YET retaining your preferred exposure setting. This factor is constant when we consider the film speed to be constant. Now let us see what will be the standard exposures in some standard light conditions with different film speed settings;
Here we can see that as the light intensity is reducing (from morning daylight to overcast) we are opening the aperture to the next bigger one thus allowing double the amount of light. It is worth mentioning that we can increase or decrease the exposure as per the light condition by either adjusting the aperture or the shutter speed or both.
Here we have changed the aperture for ISO 100, and for ISO 200 and 400 we have adjusted the shutter speed. It has to be remembered that the camera exposure always help us to find the correct exposure for the particular ISO setting in the camera.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Now let us find what complementary exposure is and how can it affect a particular photograph.
Aperture f/1.4 f/2 f.2.8 f/4 f/5.6 f/8 f/11 f/16 f/22 f/32 f/64 Shutter
Speed
1/2 ¼ 1/8 1/15 1/30 1/60 1/125 1/250 1/500 1/1000 1/2000
In the above chart suppose for a particular film speed and in a particular light condition, an exposure of f/11 and 1/125 sec is found to be perfect. Now if we change the aperture to f/8 which means we are allowing one stop more or double the amount of light, to maintain perfect exposure we have to reduce the light half by adjusting the shutter speed to 1/250 sec. So f/8 & 1/250 is a complementary exposure to f/11 & 1/125 as both gives same amount of light to the film.
Similarly the other pairs of same colour are also complementary exposure to the original exposure in red and since all the pairs are giving the same amount of light, photographs exposed with all the pairs should be same. But it is not so in actual condition. This is because photographs taken with wider aperture such as f/2.8 will have shallow or less depth of field thus causing unsharp image while images taken with faster shutter speed will freeze object movement in the frame.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
So understanding and setting exposure, according to requirement is very important for taking photographs. Sometime exposure compensation is also used to take intentional under or overexposed photographs for achieving a desired effect.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
-2 -1 0 +1 +2
If the camera functions automatically, the Exposure Compensation lets you to lighten or darken the photograph. To lighten a photograph, you increase the exposure; to darken a photograph, you decrease the exposure. The amount you increase or decrease the exposure is specified in "stops." For instance, increasing the exposure 1 stop, you indicate +1 to open the aperture or slow down the shutter speed. It‟s easy to use exposure compensation because you can preview your changes on the LCD monitor.
6. Types of camera
According to technology there are – 6.1 Film (Analog) Cameras, and 6.2 Digital Cameras.
Both kinds of cameras functions on same principles except the image capturing principles and some few minor differences. Presently we will discuss about various kinds of film cameras.
A film camera is made up of three basic elements:
1. Optical (the lens) 2. Chemical (the film)
3. Mechanical (the camera body)
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
7. Film Camera
Film cameras can be broadly classified into three types as per their size, mechanism, utility:-
View cameras
Point & Shoot Cameras
Twin Reflex Cameras (TLR)
Single Reflex Cameras (SLR)
Specialty Cameras
Let us study each of them in detail:-
7.1 View Cameras
View Cameras or Large Format Cameras --
View cameras are built like an accordion, with a lens in the front, a viewing screen in the back and flexible bellows in between. The film used in these cameras are quite large with sizes ranging from 4x5”, 5x7” or even 8x10”. These cameras give sharp details and what we see in the viewfinder is exactly what we get on the negative. In these cameras we can change the position of the lens and the film relative to each other to correct distortion.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
View cameras are bulky and must be used on tripods. We have to use black focusing cloth at the back as the image on the viewfinder is not so bright and appears reversed and upside down. Rapid set up and shooting with these cameras are difficult. These are normally used for commercial studio photography, landscapes and architectural photography.
7.2 Point and Shoot Cameras (P&S)
The viewfinder provides a rough idea of what is in view, but not the real image. These cameras are easy to handle with simple features.
P&S Cameras can be categorized into two types: Compact and Rangefinder cameras.
Compact Cameras
A camera, as small/compact as possible, with built-in features such as automatic exposure, flash, auto or fix focus, easy film loading & film advance for easy picture taking can be described as a Compact or Point & Shoot Camera.
Some type of compact cameras have a fix-focus lens, but most of the compact cameras have auto focus feature, though some of them have zone-auto focus, which means that the focusing distance from infinity to close-focus will be step by step in a few stages only.
More advanced 35mm cameras have some control over focus and exposure. Focusing mechanisms ranges from guessing at the distance and setting the lens to sophisticated autofocus units.
Most of these 35mm cameras have a viewfinder that does not keep an eye out through the lens. This leads to two problems. Firstly, we may not be able to see exactly what the film sees due to parallax, this is a particular problem for close ups.
The second problem only happens with the cameras whose lenses have a zoom feature;
unless the viewfinder is fairly sophisticated, you will not see the effect of zooming.
Many of these cameras are small, light, and weather or waterproof. They make good
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
backup cameras or cameras to carry into places you just don't want to carry a bigger camera. Without the zoom feature, they are more suitable for scenic picture capturing.
Rangefinder Cameras
These cameras are called "rangefinder" cameras because they focus using a dual-image range finding device. Turning the focusing ring superimposes two images in a line to give perfect focus. While using a rangefinder camera, the user never look through the lens but focuses and composes through a window, which is present on the top right, just like on a disposable camera.
A. Beam splitter (semitransparent mirror)
B. Light-gathering window C. Frame lines
projection/parallax compensation unit D. Frame lines projection
semitransparent mirror E. Rotating
mirror/pentaprism F. Viewfinder
G. Viewfinder frame H. Static Image I. Secondary Image
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Rangefinder cameras differ from the SLR‟s remarkably as they do not make use Through-the-Lens (TTL) viewing and focusing, although most modern Rangefinder cameras have TTL metering. Instead, focusing in Rangefinder cameras are executed via a rangefinder mechanism that can be either coincident (“classic” rangefinders) or electronic.
The accuracy of focusing depends on the effective base length, which in case of RF cameras is derived from physical distance between beam splitter and rangefinder mirror/pentaprism (see diagram above) multiplied by the magnification of the viewfinder.
The larger and effective base length, the more accurate the rangefinder is.
The middle rectangular window just above and to the right of the lens on most of the rangefinder cameras collects light to make the frame lines brighter. Beam splitter (A) and rotating mirror/pentaprism (E) form two images in the viewfinder – static (H) (through the beam-splitting mirror) and secondary (I) (through the rotating mirror). The lens is linked with the (E) via moving camera at the lens‟s base, therefore while rotating the focusing barrel one sees the secondary image moving across the viewfinder. When static and secondary images match the focus is achieved.
Focus control for optical coincident-type rangefinders
Out-of-focus In focus
(no match of overlay image) (overlay image matches)
Advantages of Rangefinder Cameras
The image quality of Rangefinder cameras is good because there is no flipping mirror.
As flipping mirror is not present in it, so there is much less vibration to blur hand-held images. At speeds of 1/30 to 1/8, the flipping mirrors of SLRs often gives blurred images made from tripods unless a mirror lock-up is used.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Rangefinder cameras have accurate focusing for wide and normal lenses. Rangefinder works well without the extra weight of prisms focus screens and flipping reflex mirrors.
As SLR mirrors flip up to take a picture, its viewfinders goes black at the most important point: the point at which an image is recorded forever.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Rangefinder cameras viewfinders never black out, so you always know the subject's expression as it is recorded, especially with flash. While using a rangefinder, you press the button, and it goes. You have captured the peak of the moment, forever. But while using an SLR, the mirror has to get out of the way before the shutter can open up. But by the time the SLR‟s mirror gets out of the way, your conclusive capturing moment is gone.
Disadvantages of Rangefinder Cameras
The major disadvantage of Rangefinder camera is that we never come to know what we are getting with rangefinder cameras as the viewfinder is separate, and it sees from a different point of view. For regular shots at regular distances, this is not important, but for the long lenses and major use, rangefinders give us no clue to what we are capturing.
Even with a LEICA rangefinder, we never really know what has been exposed until the final image is printed. We never come to know or any hint of Depth of Field with a rangefinder camera, in whose viewfinders everything is always in perfect focus. With a rangefinder camera and a long lens, we're usually looking at only a small cut-out frame in the finder.
7.3 Twin Lens Reflex Cameras (TLR)
A twin-lens reflex camera (TLR) is a type of camera with two objective lenses of the same focal length. One of the objective lens is the photographic (lens which takes the photograph), while the other lens is used for the waist-level viewfinder system. In addition to the objective, the viewfinder comprises of a 45-degree mirror (the reason for the word reflex in the name), a matte focusing screen at the top of the camera, and a pop- up hood surrounding it. The two objective lenses are connected, so that the focus shown on the focusing screen will be exactly the same as on the film. However, many low- priced TLRs have fixed-focus models. Most of the TLRs use leaf shutters with shutter speeds up to 1/500th sec with a B setting. For practical purposes, all TLRs are film cameras, most often using 120 films, although there are many cameras with other formats. Expensive TLRs have a pop-up magnifying glass to assist the user in focusing the camera. In addition to that, many have a "sports finder" consisting of a square hole punched in the back of the pop-up hood, and a knock-out in the front.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
7.4 Single Lens Reflex Cameras (SLR)
Single-lens reflex cameras or SLR‟s are more complex form of cameras, than any other types of camera. The viewfinders of other camera types are quite simple and usually have nothing to do with the main lens of the camera.
In basic types the viewfinder is just a rectangular-shaped hole and in more complex types the viewfinder is somehow connected to the main lens for focusing purposes (twin-lens reflex (TLR) cameras for example), but still these systems are simpler than SLR cameras.
So, how does a SLR camera work or what makes it so complex? The key parts for the light to move through the camera are: lens, mirror, focusing screen, prism and eye piece.
The lens is made up of several optical elements to form the image on the film. The mirror is small, light and capable of moving up and down. Focusing screen is made up of ground glass and when image is projected on it, the image becomes visible and doesn‟t just go through as with regular glass. Sometimes the focusing screen also has some features that will help us focus the picture.
The prism (its shape may vary, but the idea remains the same) is made up of glass and it reflects the image from the focusing screen to the eye piece, which itself is just a piece of glass or simple lens, that we are looking through.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
The red arrows are showing the path of light during the composing of the photo and the green arrow showing the path after actually pressing the shutter release button for taking the photograph. Mirror moves up, shutter opens up, shutter closes down and mirror moves back down are the actions that take place on that photo taking process.
Have you noticed that when you are taking a photograph with a SLR camera, the viewfinder goes black for a moment? That is the mirror in upper position closing the focusing screen and preventing an extra light from getting through the eye piece while the shutter is open.
As you can see, the image is mirrored. If there is another mirror instead of a prism, the image in the viewfinder would be upside down. So, the prism mirrors turns the image back straight. But still, if one mirror flips the image upside down and the second one would turn it around again, the image would still be on its head? And actually, all images on the film are also upside down as the last photo shows.
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
To control exposure in a SLR camera, one must know how to control the Shutter Speed, Aperture and set the Exposure meter to find out the correct exposure. To start with controlling Shutter Speed, there are both analog dials and digital display to set the shutter speed as follows:
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
Similarly for controlling aperture, older cameras had aperture control on the lens ring and the electronic cameras had aperture control from display window as follows:
The purpose and effect of controlling the aperture and shutter speed has already been explained earlier and needless to say that these two are the major factors for controlling the required exposure both in a film and a digital camera.
The light meter or exposure meter inside a camera both in an old SLR camera and the latest camera helps us to achieve correct exposure and sometimes gives us automatic exposure in the program or automatic modes. To make the exposure meter work correctly we must set the film speed accordingly. Let us see how to set the film speed in a SLR camera:
FORENSIC SCIENCE PAPER No.7: Criminalistics & Forensic Physics MODULE No.26 : Basic Principles of Photography
The film speed of a SLR camera can be set manually in the range of ISO 12 to 6400. This calibrates the built in exposure/light meter to calculate the amount of light required for a particular scene and help the photographer to determine exposure. Film speed of the loaded film can also be known through the DX film cod reader in the chamber where the 35mm film is loaded in the camera.
When the exposure setting is proper or the light is correct, the red bar is at the middle showing correct exposure.
When the exposure setting is under or the light is less, the red bar is at the (-) side showing under exposure. Here we have to open aperture or reduce/slow down the shutter speed.
When the exposure setting is over or the light is more, the red bar is at the (+) side showing over exposure. Here we have to close aperture or increase/ use fast shutter speed.
Metering system optics
There are three Auto Exposure (AE) metering sensors in different locations are used for the six metering modes. The 16-zone metering sensor above the eyepiece is used for 16-zone Evaluative, Partial, and Spot & Center-weighted Average Metering. At the bottom of the mirror box, a metering sensor is used for Fine Spot Metering. At the bottom of the mirror box, the three-zone TTL flash exposure metering sensor is used for off- the-film ("OTC") metering. Some cameras have multi metering modes including off-the-film flash metering. The metering mode can be selected (Five metering modes easily switchable) to suit the user's objectives.
