This is all 6 parts, concatenated. Depite the subject line ;) Andrew From: vibard@utopia.resntl.bhp.com.au (David Barnes) Subject: Int. to photography Pt 1 Date: Tue, 2 Mar 1993 06:33:55 GMT Lines: 238 On one of my rare visit to this news group I noted a posting that expressed dismay in the lack of informative articles to be found and suggested that if anyone felt motivated to post a few more expansive articles it may be appreciated. Having been a professional photographer for the past 10 years I tend to avoid this group, as it's often the forum for beginners problems etc., which is fair enough. But as I said, I still visit rec.photo from time to time to answer a question or seek out a pearl of wisdom from a posting. So in the spirit of global communication, after all that's what the networks all about, I would be happy to post a series of articles on photography that I compiled a few years ago for an introductory photographic course at the local technical college. So please forgive me if they are a little out of date or not advanced enough for some, they were intended for people who were just starting to get into photography. I know that I would appreciate similar articles being posted in other groups, I read, where I consider myself a rank beginner and am often reluctant to post questions that would appear too simple. Anyway enough of the prattle here is the first of the series, let me know if this proves useful and I will post the rest over the next few weeks. All the best David PS Sorry if they are a little disjointed as line drawings and photographs came with the articles and I am not sure of how to send these electronically. PHOTOGRAPHIC TECHNIQUES ONE COURSE AIMS This course is designed to meet the needs of the inexperienced photographer by developing an appreciation of photography as an artistic medium and understanding it's underlying procedures and the technical terminology. It covers elementary theory, types of cameras, accessories, film exposure techniques and pictorial composition. Week 1 Introduction; camera types, advantages and disadvantages, the parts of the camera and their functions. Week 2 Understanding shutter speeds and apertures Week 3 Exposure, methods and calculation in difficult situations. Week 4 Camera lenses, types and applications. Week 5 Flash photography. Week 6 B&W and colour film, camera accessories and filters. Week 7 Composition, lighting and basic portraiture techniques. Week 8 B&W film processing. Week 9 B&W printing and test. TYPES OF CAMERAS CAMERA COMPONENTS All cameras, no matter how simple must have the following parts to be effective: 1. A light tight place to store the film before and after exposure - The body. 2. A device for focusing light rays onto the film - The lens. 3. A method of controlling how much light reaches the film - The aperture. 4. A method for controlling how long the film is exposed to the light - The shutter. 5. A method so the photographer can see what will be recorded - The view finder. 6. A method to hold and move the film as required - The transport. TYPES OF CAMERAS Over the years there have been many camera designs produced, for both recreational and professional work, but generally all camera's fall into one of the following categories; 1. Viewfinder or range finder camera's. 2. SLR camera's. 3. Twin reflex camera's 4. View camera's. For the amature photographer the view finder, range finder and primarily the SLR camera are, the camera's of choice, the twin lens and view camera have specific uses for the professional photographer which will be discusssed in the advanced course. THE VIEWFINDER OR RANGEFINDER CAMERA The viewfinder or rangefinder camera classification covers a whole range of camera's on the market, from simple disposable cameras through to sophisticated compact cameras. The one feature that groups all these cameras together is that they all have a separate viewfinder to the lens. Usually a simple glass viewfinder to the above right or left of the main lens which allows the photographer an approximation of what the lens is "seeing". With the less expensive cameras the separate positioning of the lenses introduces a problem called parallax error. Parallax error occurs mostly in close-up photography when the photographer does not receive an accurate indication of the subjects position, relative to the lens, through the viewfinder and often result in parts of the subject missing on the final photograph. A good example of this occurring would be a portrait, the viewfinder will indicate to the photographer that the subject is correctly positioned, but the actual lens may not record the whole subject due to its lower position relative to the viewfinder, resulting in the subjects head missing in the final photograph. The problem of parallax error is overcome in more expensive compact and rangefinder cameras, which incorporate compensating viewfinders, these adjust the viewfinder for the distance the subject is away from the camera. Often it can be an advantage to have a separate viewfinder in the camera, one of the problems that SLR cameras have, is focusing in low light conditions. The compact camera with it simple viewfinder allows a lot more light to reach the eye, as the light does not have to pass through multiple glass elements in the lens and a focising screen as it does in a SLR camera. Also rangefinder and compact cameras operate more quietly than SLR cameras as they don't have an internal mirror. This can be very helpful with nature and candid photography where noise may alert your subject. Compact cameras have come a long way over the last few years and incorporate many advanced features, such as variable focus length lenses, programmable flashes and advanced exposure control. But even so they rarely offer the flexibility of the modern SLR camera. On the other hand rangefinder cameras have continued to be used by many professional photographers as they incorporate the flexibility of the SLR as well as being very quiet. In fact some of the most expensive 35mm cameras are rangefinders. ADVANTAGES OF THE COMPACT/RANGEFINDER CAMERA * There is a model available in every price bracket. * They are usually simple to use. * They require less maintenance than more sophisticated cameras. * They are light and easily portable. So they are excellent units for catching quick, informal shots and have a strong appeal for family and domestic use. * They provide excellent viewing at low light levels. Disadvantages of the compact / rangefinder cameras * Parallax error due to the different positions of the users eye and the camera lens. Although this problem is overcome in more expensive models with a compensating viewfinder. * Little control over focus, aperture size and shutter speed (except in the more expensive models) * They require plenty of light, so catching movement or photographing subjects indoors is difficult. Some units come with small flash units which partially overcome these problems. * Most are unable to take close-ups, 1 to 1.5m being the closest most compacts are able to deal with. THE SLR CAMERA The SLR camera is by far the most popular camera for professionals and serious amateurs covering both 35mm and 120 format. The letters SLR stand for single lens reflex, which means that the viewfinder and image capturing lens are one in the same. Having been the most popular camera design since the mid 60's the SLR has had a great deal of research and development placed upon it, resulting in very sophisticated models now being available to the consumer The SLR solves many of problems associated with the compact camera. Parallax error is corrected with a built in mirror and prism that allows you to view a subject through the same lens that takes the picture. Although this addition makes the camera heavier and more complex, as well as more expensive, it increases the camera's potential. In close up photography for example, you are able too see exactly what you are photographing without any concern as to whether part of the image will be missing in the final photograph. SLR camera's also allow you to attach a large range of lenses to the camera body which gives almost unlimited picture taking potential, from ultra wide angle shots to extreme telephoto pictures which will capture action from great distances. Depth of field can also be easily calculated with depth of field preview buttons and markings engraved on most lenses. Also far more accessories are available for the SLR camera than other camera systems. On the negative side the SLR is noisy when compared to the compact camera due to the action of the mirror, so many close up candid opportunities may be lost. Light is also lost with the mirror and focusing screen, so focusing can be much more difficult in low light conditions. SLR MAIN ADVANTAGES * No parallax error. * Quick and easy to focus. * Viewfinder system works well with all focal length lenses. * Whatever the lens sees the viewer sees. * Depth of field can be visibly seen all over the image area. * Allows a larger variety of lenses relative to the viewfinder. SLR MAIN DISADVANTAGES * Heavier and less compact. * More complex with more moving parts (more things to go wrong). * Much louder due to the moving mirror, this is a drawback when unobtrusive photography is required. * Focusing is not as good under low light conditions, particularly with slower lenses. END OF PART 1 -- -------------------------------------------------------------------/\/\--- David Barnes, Photographic Department / / /\ BHP Research - Newcastle Laboratories, Australia./ / / \ Snail : P.O. Box 188, Wallsend 2287 / / / /\ \ Tel : +61 49 510521 Fax: +61 49 513740 \ \/ / / / Internet: vibard@resntl.bhp.com.au \ / / / ------------------------------------------------------------------\/\/\/-- Subject: Int to photography 2 Date: 11 Mar 93 03:41:37 GMT Here is the second part in the series of introductory photography lessons. Sorry that the diagrams that are referred to cannot be included. CAMERA COMPONENTS Inside the camera When you look in the viewfinder of an SLR camera, you are actually seeing through the lens. The diagram below shows how an image is transported through the lens to both your eye and film. If you follow the line you will see that as the light rays collected by the lens enters the camera body, they are reflected upward by an angled mirror into a prism housing on the top of the camera. Due to the characteristics of lenses the image is turned upside down and reversed on passing through the lens. The mirror turns the image right side up, and the prism turns it around and reflects it into the eyepiece. By the time it reaches your eye, the scene looks like the one you see without the camera, which will then appear in the final photograph. Other than to compose your picture the other purpose for looking through the viewfinder is so you can accurately focus your image. To help you do this a focusing screen is placed just under the penta prism and above the mirror. It is actually the focusing screen you are looking at when you are focusing the camera. For the system to work the focusing screen is the same distance from the lens as film plane, so if the image appears sharp on the focusing screen it will be sharp on the film plane. In the centre of the focusing screen there are two devices that appear as circles, one within the other, to help you accurately focus the image. The centre one is made from two small triangles of glass, this is used when your subject has some sort of line in it, such as a tree branch. If the camera is correctly focused, any line that passes through this area will appear unbroken, if on the other hand the image is not focused, the line will appear disjointed as shown in the diagram. The outer circle is called the micro prism and is formed from thousands of pyramids of raised glass, the micro prism is used where there are no lines in the picture. If the subject is correctly focused the micro prism will appear clear, if incorrectly focused the image will appear as a blur through the micro prism. With the advent of auto focus lenses these aids have mostly been replaced with a small square in the centre of the viewfinder to indicate what part of the image the lens is using to calculate the focusing distance. When you press the shutter button to take a picture, the angled mirror flips upward to permit light to pass to the back of the camera, where the film is. Simultaneously, the shutter, a pair of curtains just in front of the film, opens to let the light hit the film. The shutter remains open for a precise amount of time, which is determined when you set the shutter speed. As soon as the shutter closes, the mirror drops back to it's normal viewing position. Because the mirror rises to allow the image to pass through to the shutter and then to the film, the viewfinder goes black momentarily when you take a shot. Most modern SLR's have a built in exposure meter. One or more photo cells located in the light path measure the intensity of the light reflected by the subject and admitted by the camera. On an automatic camera, the shutter speed or lens aperture, or both, are set automatically, according to this measurement. On a manual camera, or automatic camera in manual mode, you set the shutter and aperture by hand to achieve the proper exposure. Correct combinations of the two are indicated in the viewfinder by a matching needle, light-emitting diode (LED) or liquid crystal display (LCD). On an automatic camera, the aperture or shutter speed or a combination of the two chosen by the camera will usually be displayed in the viewfinder. Refer to your instruction manual for an explanation of your camera's viewfinder display. OUTSIDE THE CAMERA The exteriors of most 35mm camera's have an almost bewildering array of dials, levers, rings, and other controls. But they are all easy to use once you understand their function. Two basic controls, the focusing and aperture rings, are on the lens; the aperture will be looked at more closely in Depth of Field. The other basic control, the shutter speed, allows you to choose the amount of time the shutter will remain open. On a SLR the shutter speed dial is usually a small cylindrical control on the top of the camera, to the side of the prism. Some newer models have buttons that change the shutter speed, an LCD display usualy indicates the chosen speed, on certain older models, a ring on the lens barrel itself may control shutter speeds. The shutter speed function will be looked at more closely in the Shutter speeds section. You activate the shutter by pressing the familiar shutter release button. It is located on the top of the camera, where you can press it easily with your right index finger. Most shutter release buttons are threaded to accept cable releases, an accessory that enables you to trigger the shutter without touching or jiggling the camera, often at a distance, refer to the section on Camera accessories. With many of the newer camera's on the market, the cable release plugs into the side of the camera and is activated electronically. Many camera's also have a self timer lever, which delays the exposure for 8 to 10 seconds for you to include yourself in the photograph, once again it, with many modern camera's this function is set electronically on the camera. Most SLR's have a device called the film advance lever, located on the right side of the top of the camera. When you move the lever, an unexposed frame of film moves forward out of the cartridge, into position for the next picture. Many newer SLR's and compact cameras now have internal motors that automatically advance the film when you take a photograph. In either case, advancing the film, changes the film counter, which is adjacent to the lever or shutter button or displayed on a central LCD panel and indicates how many pictures have been exposed on the roll. On the left side of the camera top is the rewind knob, used for winding the film back into the cartridge. This is also automatically done on many camera's. Before this knob will work, you must disengage the film advance mechanism, in most cases with a small rewind release button on the bottom of the camera. When you have rewound the film, the same knob is usually pulled up to open the back of the camera so that you can remove the film. Most modern camera's also have several controls for their built in exposure meters. One is simply a switch for turning the meter, and the camera itself, on and off and is usually on the top of the camera. Another lets you adjust the meter for the sensitivity, or speed, of your film. On most SLR cameras this film speed dial is located around the rewind knob. You should set this dial according to the ISO number of the film you are using. With the event of DX coding on film canisters which allows sensors on modern camera's to identify the ISO of a film automatically, manual setting of ISO is becoming less common. On many cameras the dial also has an exposure compensation feature built into it (marked 0, +1, -1 etc.), often engaged with a small release button that allows you to override the automatic exposure system or bracket your exposures. Finally, the meter of an automatic camera may be effected by an exposure mode selector switch, which allows you to choose automatic and manual exposure modes and is frequently integrated into the shutter speed dial. On a few recently released cameras very specific exposure parameters can be programmed into the camera, via cards you insert into the side of the camera, the cards contain programmes for the specific needs of sport, portraiture, wildlife photography etc. There are two ways to connect an electronic flash unit to a camera, both of which establish electrical contact, synchronising the flash with the shutter. One is the hot shoe outlet, almost always located on top of the prism. On most SLR's you can also plug you flash into an outlet on the front of the camera called the X sync. Also found on the front of many SLR's is a depth of field preview button or lever that allows you to view the scene through the aperture you have selected to examine the zone of sharpness it will provide in the scene, and a lens release button that permits you to unlock and remove the camera's lens. Although there are fewer elements on the back and bottom of a 35mm camera than on the front and top, it's just as important to understand their functions. The most significant feature on the back is the viewfinder eyepiece, through which you compose and focus your picture. On nearly all SLR's, the viewfinder is located behind the prism in the centre. On most range finders, the viewing window is found more towards the left. If you wear glasses and have trouble seeing through the viewfinder with them on, you may wish to investigate the possibility of getting a corrective lens for your camera's eyepiece. Rubber eyecups are also available to prevent the camera from scratching your glasses. On the bottom of the SLR three main components are found, the small button for disengaging the rewind button as discussed before, tripod mounting socket and the compartment for placing the batteries in. The battery compartment lid can be usually unscrewed with a coin. You should replace the battery once a year to avoid corrosion. END OF PART TWO Subject: Int to photography 3 Date: 14 Mar 93 04:35:13 GMT Here is part three of the introductory photography course SHUTTER SPEEDS The shutter is a mechanical means of controlling the amount of time light is allowed to pass through the lens to the film. The period of time is known as the shutter speed. Shutter speeds are calibrated in seconds and fractions of seconds i.e. 1/2 1/4 1/15 1/30 1/125 1/250 1/500 Each shutter speed is doubling or halving the previous one and has a direct relationship with the aperture. The first basic skill in using the shutter is being able to judge the slowest shutter speed that will do the job. In most situations that depends on how active the subject is, but at the slower shutter speeds the camera sets the limit. Most photographers tend to think in only three dimensions. We see the subject in front of us, we look at the surroundings, we check out the background to see what sort of depth of field we need, or weather we should consider changing camera position to make it less obtrusive But this, three - dimensional view of the world is not complete. TIME, the fourth dimension, also plays a crucial role in photography. Careful consideration should always be given to the use of appropriate shutter speed for each photographic situation as your choice of shutter speed can have a dramatic effect on how your final photograph appears. Fast shutter speeds can be employed to stop subject movement, a good example is sport photography. For most sports a minimum shutter speed of 1/250th is needed to effectively stop all movement. Another requirement of sport photography is the need to fill the camera's frame from a distance, which means using a lens of around 300mm focal length or more. Due to the magnification of long lenses such as the 300mm lens any camera movement is greatly enhanced so once again a fast shutter speed would be required to stop any blurring caused by the camera. A rule of thumb for selecting the appropriate shutter speed to stop lens movement is to turn the lens focal length into a shutter speed, so a 300mm lens would require a shutter speed of 1/300th of a second or faster to avoid vibration. With very fast moving subjects such as cars another problem you will encounter is shutter release time lag. There is a delay of 40-60 milliseconds between depressing the button and the shutter opening, to allow for the diaphragm to close and the mirror to swing up. It doesn't sound long, but a car moving at 100km/h, for example will have covered almost 2 meters in this time. If you plan on shooting a lot of motor sport practice will allow you to obtain pin sharp pictures. Much also depends on how the subject is moving, relative to you. If it is coming towards you, a comparatively slow speed of 1/125 may freeze the action. If it is travelling across your line of sight, a faster shutter speed may be needed to avoid blur. Another alternative is to pan your shot, panning, or moving the camera with the subject to keep it sharp and blur the background, creates a real sense of movement. To pan, select a shutter speed of 1/15 to 1/60s. Hold the camera firmly against your face and focus the lens on the point where you expect the subject to pass. Start moving the camera before you trip the shutter and continue the movement after the exposure is over. Not all pictures are best taken at high shutter speeds, using slower shutter speeds you can create all sorts of special effects. Streets and highways at night are popular subjects .The moving lights of cars draw streaks across the frame. Shutter speeds of 4 to 10 seconds are ideal for this situation. Don't worry if you have an older camera as most were made with a "B" setting, at which the shutter will be opened as long as the shutter button is depressed. Flowing water is a subject that which is greatly influenced by shutter speed. At 1/1000s, you can freeze every droplet of water in a waterfall whereas at 1sec only streaks of white are visible. It really depends on what sought of effect you want to achieve. On other occasions, such as taking a portrait, the choice of shutter speed is not as critical as your choice of aperture, so a medium speed such as 1/30th or 1/60th of a second will be adequate to avoid any movement in your subject. THE FOCAL PLANE SHUTTER There has been many shutter designs through history but the common design for SLR camera's is the focal plane shutter.. This type of shutter is positioned as close as possible to the focal plane. In it's simplest form it consists of an opaque blind with a slit which makes the exposure as it is driven past the film. Exposure duration is controlled by the adjustment of the slit width and blind speed or both. Modern focal plane shutters have two blinds, one with an opening in it which, when the shutter is fired moves to a position allowing light to strike the film and another which, at the end of the exposure time, moves across the opening to stop the light striking the film. ADVANTAGES OF THE FOCAL PLANE SHUTTER Focal plane shutter enable very fast shutter speeds to be obtained. Some reaching as high as 1/4000th of a second. Because this type of shutter is positioned at the focal plane within the camera body, a complete range of lenses can be used without shutters. DISADVANTAGES OF THE FOCAL PLANE SHUTTER Focal plane shutters have many advantages but it is very important to recognise it's disadvantages and their effects on photography. It's only at slow shutter speeds that the shutter exposes all the film surface at the same time. At moderate and fast shutter speeds the second blind has started to close before the first blind has fully opened. This creates problems when using electronic flash because the duration of an electronic flash is extremely short so when the flash fires only the part of the film opened to the light by the slit of the shutter will be exposed. Modern high quality 35mm cameras will allow speeds as high as 1/250th to be used whilst still exposing the entire frame. The other problem created by focal plane shutters is one of distortion which is caused by the movement of the image during exposure. Focal plane shutters also tend to be noisy in operation and can be rather bulky. Technology continues to improve in these areas. END OF PART THREE Intro Part Four Here is part four of the introduction to photography, sorry if the drawing is a bit rough but I felt that it was important to include something to help explain hyperfocal distance. DEPTH OF FIELD The ability of the camera lens to vary the amount of the scene that appears in focus, depth of field, is one of the most useful creative tools available to the photographer. Appropriate use of depth of field can often "make or break" a photograph. Say for example you were taking a head and shoulders portrait of a friend in their back yard, unfortunately, their yard leaves a lot to be desired, in terms of attractive backgrounds for the portrait. But with the depth of field control of your lens you can over come these difficulties, by choosing a shallow depth of field, the resulting picture should result in only your friend appearing in focus with the unattractive background no more than an indistinct blur. In other situations it may be desirable to have as much of the scene in focus as possible, such as photographing family members on holidays, so people who are looking at the photograph will be able to see clearly where you and your family were. So it is always important to consider the appropriate depth of field required before taking each photograph. DEPTH OF FIELD CONTROLS There are three main factors that control the how much depth of field your lens produces in a given situation, these are the aperture setting on the lens, your distance from the subject and the focal length of the lens you are using. Aperture is critical to depth of field. The aperture of the lens is usually controlled via the ring closest to the camera body. The aperture itself is an adjustable diaphragm, a series of overlapping metal blades that operate together much like the iris of the eye. The numbers on the ring refer to a particular aperture, the numbers themselves are actually fractions which refer to the size of the aperture relative to the size of the lens. Thus an aperture of f16 produces an aperture hole 1/16th the size of the lens. Apertures work in factors of 2 with each other, the apertures each side of your chosen aperture either admits twice as much or half as much as your chosen aperture, so f11 allows twice as much light into the camera as f16 and f22 allows only half as much light to reach the film as f16.The amount of light that a particular aperture admits is consistent no matter what lens is used with your camera, which makes life easier in situations where you have calculated your exposure and you then decide to change lenses. The smaller the aperture (or the larger the number on the lens barrel) the greater the apparent depth of field. At f16, for example, most normal (50mm) lenses focused at a point 3 meters away will make the scene appear sharp from 1.5 meters to infinity. On the other hand if we were to choose an aperture of f2 under the same conditions, only the subject will appear sharp, both the foreground and background will appear blurred. Subject distance also affects depth of field. In general, the closer your subject, the shallower the depth of field. Even at f16, if you focus on a subject 1 meter away with most normal lenses, the depth of field will be less than 30cm, at f2 if this was a portrait your subjects eyes may be in focus while the nose and ears are blurred. As you back away from a subject the depth of field increases rapidly. The focal length of a lens plays a role in depth of field too. The shorter the focal length, the more depth of field you will get at a given aperture at the same subject to camera distance. Thus a 28mm wide angle lens set at f11 produces greater depth of field than a normal lens set at the same aperture and the normal lens produce greater depth of field than a 200mm lens. CALCULATING THE DEPTH OF FIELD When you change the aperture ring on your camera, neither the brightness nor the depth of field of the viewfinder image changes. This is because an SLR keeps the lens open to its maximum aperture until you press the shutter release, so you have the brightest possible viewfinder image. So the scene you view through the lens is at the cameras maximum aperture, not the aperture you selected. To compensate for this many cameras provide a depth of field preview button. When you press it, the aperture closes down to the f stop you have set. Although the viewfinder will become darker, unless you are shooting with the lens wide open, you can see the actual zone of sharpness at you selected aperture. Another means of calculating depth of field is by using the distances engraved on you lens barrel. Either side of the focus mark on the barrel, aperture points are marked, starting with f4 closest to the focus mark leading out to f16 or whatever the smallest aperture of the lens is. Once you have focused the lens, the distance falling between the two appropriate aperture marks will appear sharp in the final picture. HYPERFOCAL DISTANCE There is another method of increasing your depth of field without altering the aperture, focusing distance or lens. This is by using the depth of field scale on your lens barrel and focusing on the hyperfocal distance. Using your hyperfocal, distance can often be very difficult for the new photographers as often when you set you point of focus for the hyperfocal point your subject appears out of focus and you are required to trust in the lens optics that the subject is in focus, without any visual confirmation. In the example in the below the first drawing shows how most people would set the lens for focusing on a subject 10 meters away. The central line (the point of focus) is aligned to the 10 meter distance marking on the lens barrel. The aperture is set for f11, so using the depth of field scale as explained earlier, we know that distances between the two f11 engravings on the depth of field scale will appear in focus in the final photograph. In this case everything from 4 meters to past infinity. If in this situation you still required more depth of field, and for various reasons you couldn't use the other methods as describe earlier what you can do, by using hyperfocal distance, is set your point of focus to 4 meters as shown in the second drawing. As a result of this new point of focus the distances that fall between the f11 engravings are 2.5 meters to infinity. So in this case by using hyperfocal distance your depth of field has been increased by 1.5 meters without having to alter any other controls Although it can often difficult step to start thinking in terms of hyperfocal distance, it's worth keeping in mind for difficult depth of field situations you may encounter in your photography. 2 3 5 10 0 M DISTANCE SCALE ON LENS l l l l * l l l APERTURE MARKINGS 16 11 8 4 4 8 11 2.8 4 5.6 8 11 16 APERTURE RING 1.5 2 3 5 100 M l l l l * l l l l 16 11 8 4 4 8 11 16 2.8 4 5.6 8 11 16 END OF PART FOUR Subject: Int to photography 5 Date: 30 Mar 93 07:30:28 GMT Sender: news@resntl.bhp.com.au (Usenet news system) Lines: 184 Here is part 5 in the series Introduction to photography. Hope you enjoy it! Exposure Films differ greatly in their sensitivity to light. Some require a lot of light to record an acceptable image, while others need much less. If your film receives the proper amount of light, the final image will reproduce your subject in it's proper tones and colours. But if the film gets too much light (over exposure), the image will be pale and lacking in detail; if it gets too little light (under exposure), the image will be dark and muddy. To avoid under and over exposure, it's important to understand how to use the two controls that adjust the amount of light reaching the film, the aperture and shutter speed. Exposing film to light can be compared to filling a bucket with water from a tap. You can open the tap wide and fill the bucket quickly, or open it only a little and let the water trickle slowly. The two variables are how much you open the tap and how long you leave it on. The two exposure controls on the camera work much the same way. Like the valve on the tap, the aperture controls the size of the opening in the lens that admits the light. The shutter speed determines the length of time that the shutter will stay open to let the light pass through. The exposure meter on your camera reads the total quantity of light reflected from the subject and tells you, or the camera, which combinations of shutter speed and aperture will produce the correct result on the film you are using. Because apertures and shutter speeds work on the principal of halving and doubling as you change their setting, a variety of aperture and shutter speed combinations will produce the same quantity of light on the film surface. For example, if the camera came up with an exposure of 125th of a second at f5.6, you could change the setting by halving the shutter speed to 250th of a second and doubling the aperture to f4 and still achieve a correct exposure. By using the principal of halving and doubling your aperture and shutter speeds, you can select the creative parameters of your photograph. If you require a very fast shutter speed for a photograph you can sacrifice your depth of field by using a wide aperture to achieve this. On the other hand if a small aperture is required you can choose a lower shutter speed to correctly expose the film. Unless there is a lot of light around or you are using a very light sensitive film you will have to make a creative decision with many of your photographs as to whether you want to highlight shutter speed or depth of field. METERING PROBLEMS The different light levels of the many things you will want to photograph call for changes in exposure settings. A park scene on an overcast day, for example, requires a wider aperture or a slower shutter speed or both than does the same park on a sunny day. This is because film of a specific sensitivity to light needs more or less the same amount of light in each case to produce a well exposed image. If the illumination is even and not too dim and the subject reflects an average amount of light, your camera's meter is fairly reliable in selecting the proper setting. Keep in mind though, that a light meter is only a mechanical device designed to take a general reading of the light in a scene. In some situations, this reading will not produce the results you want. Your meter may be particularly prone to error in measuring strongly lighted scenes with bright highlights and deep shadows. In such cases, it may be best to take local readings from both dark and light areas, then choose an exposure midway in between. The meter assumes that the tone in anything that you show it will average to a medium grey (called 18% grey) and recommends an exposure that will conform to this average. But in a subject such as a beach scene, where most of the tones are light, this will result in under exposure, the meter will try to make the white beach grey. If you have manual exposure control, you can take a reading off a photographic grey card, which is what the meter is calibrated for, to avoid this error. With slide film, sometimes metering off a grey card will produce a light result, so you may want to decrease the indicated exposure by one half stop. With any film, to be on the safe side in tricky lighting situations, you should bracket your exposure, take extra pictures that give you one half or one stop more or less exposure than indicated. METERING PATTERNS It's also important to understand the metering pattern of your camera, so you can be aware if it's being adversely influenced by the various reflective levels in a part of the scene you are photographing. Currently there are 4 main types of metering patterns found in cameras today, some of the more expensive camera's actually offer a choice of metering modes. The first is centre weighted metering, this is by far the most common meter type to be found in todays camera's. Centre weighted metering considers the light levels through out the scene but gives more emphasis in it's exposure calculation to the central area of the picture, the manufactures assume that most photographers tend to place their subject in the central part of the frame so correct exposure of this area is more important than the surrounds. So it is worth bearing this in mind if you subject is to the side of the frame and the brightness levels in the centre of the frame are different to your subjects. The second type of metering pattern is the average pattern, now less common in camera's, this system bases it's exposure on all the subject area. You will generally only find this meter pattern on older camera's. Once again consideration should be made in your exposure if your subject's brightness varies widely from the overall brightness levels. The next type is spot metering. Spot metering is generally found on camera's that offer a choice of metering systems, this meter only bases it's exposure on a very small part of the scene that falls in the centre of the frame, so extreme care should be used when using this metering method. Many spot meter modes on more expensive camera systems allow you to take multiple readings, each one is stored in the camera's memory and then averaged out with the others to give you an overall exposure. This method of exposure calculation is very useful in difficult lighting situations. The last metering mode has a number of names, but the most common is multi-programme. The metering system is only found on the newer electronic camera's. Manufacturers have devised varying versions of a similar system where the camera takes several readings from over the scene and gives each a particular weighting for the exposure calculation. In essence it is very similar to centre weighted metering but this system is usually far more reliable. Exposure Modes There are four main metering modes that camera manufacturers employ with their camera systems, these are TTL metering, shutter priority, aperture priority and programme mode. Some manufacturers will only offer one system with their camera, while others will offer two or more. The number of methods offered are usually governed by the price of the camera. MANUAL METERING Manual, is the most basic of the four systems. Exposure is achieved by the built in meter reading the light through the lens. By manipulating the aperture ring and shutter speed control, the correct exposure is displayed in the viewfinder when the needle or diode is centralised or matched. SHUTTER PRIORITY The user sets the camera speed and the camera automatically selects the appropriate aperture for the given lighting conditions. To assist the photographer the selected aperture is usually displayed in the viewfinder. APERTURE PRIORITY The same as shutter priority, but this time the photographer sets the aperture while the camera selects the appropriate shutter speed. PROGRAMMED OPERATION In this mode the camera selects both the aperture and shutter speed for the photographer. On newer, more expensive cameras a "bias" may be selected, in this mode to compensate for the special needs of sport etc., where a high shutter speed is the most critical factor. If you are in the market for a new camera, and intend to use it creatively, look to purchasing either a fully manual or semi automatic camera. This way you will have control over the aperture and shutter speeds used on your camera. Which will allow you to put your own creative stamp on the image. END OF PART 5 Subject: Int. to photography 6 Date: Thu, 15 Apr 1993 22:37:59 GMT Lines: 170 LENSES One of the main advantages of the single lens reflex camera is it's ability to accept a wide range of lenses. This gives the photographer a large degree of flexibility in how he presents an image. Lenses are described primarily by their focal length. Simply put the focal length is the distance between the rear of lens and the film when focused at infinity. Although in many newer lenses this may not be the case due to advanced design. Focal length is measured in millimetres, and the standard (or normal) lens on most SLR's is 50mm. This lens is supplied with the camera because it represents the elements in a scene in the same size relationships that appear to the unaided eye and gives a reasonably broad angle of view. Lenses with a narrower angle of view than a 50mm lens are called telephoto lenses. They have longer focal lengths and bring distant objects closer. Wide angle lenses have shorter focal lengths than 50mm and encompass more of a scene from the same point. Zoom lenses provide a continuous range of focal lengths between their specified maximum and minimum limits. TELEPHOTO LENSES Telephoto lenses, which have a focal length longer than that of a normal lens, enlarge a subject in the same way that a telescope does. As the focal length increases the degree of magnification increases and a number of other interesting things happen that effect your image. The lenses angle of view becomes narrower, and provided that the subject to distance remains constant, the depth of field becomes shallower. These effects can become useful depending on the kind of image you desire. The narrow angle of view allows you to isolate a detail or illuminate a cluttered foreground. Although it makes more careful focusing necessary, the shallow depth of field is great for blurring distracting foreground and backgrounds and the perspective change can make distant elements in the landscape appear closer together or let you get a tight close-up of a face without distortion. By far the most useful of the long lenses is a medium telephoto, between 75 and 135mm. Because they minimise facial distortion and allow a comfortable distance between the photographer and subject while still providing a full frame image, medium telephoto are ideally suited to portraits. In addition they are needed in many situations in which you have to keep a moderate distance from your subject, such as taking a candid street shot or photographing architectural details. Long telephoto lenses, those with focal lengths of 180mm longer, have much more specialised uses. These lenses are usually used by sport or wildlife photographers. Both these types of photography rely on powerful magnification. Long lenses usually have a relatively small maximum aperture, often f4 or smaller, and since they accentuate camera movement, a fast shutter speed is necessary. A rule of thumb in selecting a shutter speed is to use the lens focal length as the minimum speed, i.e. if you were using a 200mm lens avoid using shutter speeds slower than 1/250th. Telephoto's of 500mm or longer are bulky, heavy and awkward to use and nearly always require a tripod. The mirror telephoto lens greatly reduces these problems. Following a principal used in the design of observatory telescopes, this lens has two curved mirrors that bounce the light rays back and forth, in effect "folding" them to pack a longer focal length into a shorter lens barrel. Although the lens is larger in diameter than a regular long lens, it's far more compact and lightweight. The price of this convenience however, is an unchangeable aperture, usually around f8 for a 500mm lens. Further to this there is a tendency for bright out of focus points of light to become doughnut shaped rings in the final image. To obtain grater magnification with most lenses, you can also use a teleconverter, relatively inexpensive tube like attachments that fit between the lens and the camera, to either double or triple the focal length of the lens. Tele converters reduce the effective aperture of the lens and usually cannot match the sharpness achieved with a real telephoto. WIDE ANGLE LENSES When you want to show more of a scene than would be possible with your normal lens, you should use a wide angle lens. With it's shorter focal length and broader angle of view, the wide angle lens achieves the opposite effect of the telephoto. Instead of enlarging and isolating part of a scene, the wide angle lens reduces it's apparent scene and takes in more of it's surroundings from the same vantage point. A wide angle lens also has a much better depth of field at a given aperture with camera to subject distance constant, than does a longer focal length lens, making it a good choice when you want maximum depth of field. Like telephoto lenses, wide angle lenses alter the perspective of a scene, but in a different way. Elements appear more distant from one another than your eyes perceive them to be. This change in perspective can cause distortion if your subject is too close to the lens or at an angle to it. An object or a person may appear longer, taller or wider than in reality, and this attenuation of space may cause protruding elements, such as a persons nose to loom. Parallel vertical lines, in particular, will converge if the lens is pointed up, diverge if the lens is pointed down. These effects can be controlled if the camera is used strait on. A moderate wide angle lens, one with a focal length of 28 or 35mm, is the most useful. These lenses generally have a fairly large maximum aperture, f2 or f2.8, making them especially useful in low light situations. Extremely wide angle lenses, 16 to 24mm, can be very effective in creating an expanse of space or deliberate distortion of shapes. Ultra wide angle lenses, known as "fisheyes", take in 180 degrees or more, far beyond what the unaided eye can see, but their shorter focal lengths will mostly only produce a circular image. ZOOM LENSES Rather than being limited to just one focal length, a zoom lens has movable optical elements that make possible a whole range of focal lengths. The control used to adjust the focal length of the lens varies. On some lenses, it's a separate ring that you turn to enlarge or reduce the image of your subject. In more recent zooms, it's incorporated into the focusing ring, and you slide the ring up and down the length of the barrel to change focal lengths. One of the advantages of these one touch zooms is that you can focus once, then slide the ring without turning it, and the lens remains focused. Zoom lenses are available in a variety of focal length ranges. The telephoto range offers focal lengths from 70 to 80mm to 200 or more, although some makers now offer lenses in the 150 to 600mm range. Another group ranges around the normal 50mm focal length, many having moderately wide angle to medium telephoto capacity such as the 28 to 80mm lens. Some wide angle zoom range as short as 24mm, although their upper end is more limited. MACRO LENSES Most lenses will not allow you to take a tight close up photograph, such as a small flower, due to the lenses optics. To over come this problem macro lenses were designed, although more expensive than conventional lenses, they offer a new world of close up opportunities to the photographer. Strictly speaking, this lens should be called a close focusing lens, since the term macro implies making an image life size or larger on film. When used by themselves at their closest focusing distance, these lenses can produce a film image that is about half the size of the subject. For most close up subjects this range is more than adequate. With the addition of extension tubes or bellows between the camera and the lens, the range of the macro lens can be extended even further to reproduce subjects at two, three or more times larger than life. The main problems associated with macro lenses is their extreme lack of depth of field and their need for a long exposure time. END OF PART SIX -- -------------------------------------------------------------------/\/\--- David Barnes, Photographic Department / / /\ BHP Research - Newcastle Laboratories, Australia./ / / \ Snail : P.O. Box 188, Wallsend 2287 / / / /\ \ Tel : +61 49 510521 Fax: +61 49 513740 \ \/ / / / Internet: vibard@resntl.bhp.com.au \ / / / ------------------------------------------------------------------\/\/\/--