A camera which is reasonably compact, easy to operate, and can take a whole range of lenses opens up dozens of new possibilities for any photographer. Telephoto lenses for sports action pictures and better portraits, wide- angle lenses for depth in sweeping landscapes and pictures in cramped spaces, or close-ups of insects using a macro (close-focusing) lens. The pentaprism SLR camera can provide all these things. It is the most popular interchangeable lens camera, widely used by amateurs and professionals alike. There are others with interchangeable lenses—for example medium format SLR cameras and some viewfinder cameras—and these are discussed in detail later on. Read the rest of this entry »
Even the most accurate through the lens exposure meter can be fooled by a subject surrounded by large dark or light areas, subjects which are predominantly back lit, or those against unusual backgrounds. These can influence the meter, providing false information about the light level. Thus the main subject is over-exposed if the meter reacts to a large expanse of black background and, conversely, underexposure of the subject results if it is back lit or surrounded by a large bright area. Read the rest of this entry »
Most modern cameras have a light meter built in. This has proved to be very popular among amateurs and professionals alike because of the speed and convenience it offers.
All exposure meters work towards the same end—to give the photographer exposure information—but the ways in which they operate vary widely. There are two basic types however: coupled and uncoupled. Examples of both systems are found in 35mm reflex and non–reflex as well as in smaller and larger format cameras. Read the rest of this entry »
You can measure the light either from the camera position or from close to the subject. The reading can be taken in two ways: using the light reflected from the subject or the incident light falling on the subject. Incident light readings can only be taken using a hand-held meter.
A reflected light reading, taken by both built-in and hand-held meters, measures the light bouncing off the subject. It can he measured either from the camera position, where you will actually take the photograph, or close to the subject. Taking the reading from the camera position will give an overall impression of the available light, including the background. But, if one part of the picture is more important than the rest, walk up to it and take the reading, or measure the light on a substitute. For example, a hand held close to the meter will represent skin tones in a portrait if similarly lit. Read the rest of this entry »
Choosing the best exposure for a picture is just as important as getting the image sharp. A beautiful holiday picture on the beach is spoiled if you cannot see details of the people in the photographs—they may be too light or dark.
A correctly exposed negative or slide will have a full range of tones from deep shadows to bright highlights. Under-expose your photograph and the darker parts of the picture will contain little detail; over-expose, and the bright parts will appear all washed out and lacking in detail. Read the rest of this entry »
Basically, there are two main types of shutter: those that work inside or just behind the lens, known as between lens shutters, including sector shutters; and focal plane shutters, which are positioned close to the film.
The between lens shutter closely resembles the aperture and is positioned between the lens elements, near the aperture blades. It is made up of two or more overlapping metal blades. which spring open for the time of the exposure and then close again. These shutters are very light and compact, and can synchronize with flash at all speeds. But between lens shutters have two drawbacks: few work at speeds of over 1/500, and they are costly to produce for cameras with interchangeable lenses. This is because each lens requires its own integral shutter and a separate means to block light from the film when the lens is removed.
Between lens shutters are used mainly on rangefinder 35mm cameras and roll film cameras. Read the rest of this entry »
Most labour-saving household appliances contain an electric motor of some description. They are the workhorse of these appliances and most of them are capable of coping with the work loads inflicted upon them. However, some motors, either through poor design or as a result of manufacturers’ cost limitations, are inadequate for the job they are required to do. Adequate or not, at some point it is almost inevitable that they will fail or simply wear out. To delay this, use the appliance with some care and attention, be aware of its limitations and carry out regular inspection and servicing. This will prevent small problems escalating into major ones
Not only do the sizes of motors vary greatly between products, so too do the ways in which they work. To diagnose faults successfully and service or repair appliances, a working knowledge of motors is essential. The following provide a basic introduction to the various types, a description of how they work, the appliances in which each may be found and their particular advantages and drawbacks. Specific problems can be found on individual appliances. Read the rest of this entry »
The speed control on this type of mixer results from the interaction of mechanical action and electronic control. Two variations of electrical control can be found but each uses the same mechanical action.
Two small spring steel plates are fixed to the cooling fan on the lower end of the armature shaft. They are slightly bowed and joined at either end by a small weight. Only the top plate is secured to the fan and shaft. When the motor rotates, the weights on each end of the joined plates are forced outwards by centrifugal force. As they are formed in a bowed configuration and joined at either end, the outward movement of the weights causes the lower plate to be forced downwards. The degree of movement is proportional to the rotational speed of the armature. This movement is used to actuate a switch on the speed control panel. Read the rest of this entry »
Unlike the pre-set speed control, variable control allows a greater variation in motor speeds. The motor is a plain AC series-wound brush motor and consequently it is incapable of any variation in speed on its own.
Speed is governed by a separate speed control unit. This unit consists of a printed circuit board with a number of solid-state components, often called the speed module or motor control module. In simple terms, this device interrupts the power supply to the motor at regular intervals. In effect, it pulses the motor. If the pulsing is increased, the motor will run faster and if pulsing is slowed, the motor will run slower. Read the rest of this entry »
The electric food mixer is truly a labour-saving appliance. Many variations can be found from the simple hand-held type to the large table-top version with additional attachments, such as juice extractor, liquidizer, vegetable peeler, can opener and grinder.
At the heart of all mains powered mixers is a series-wound brush-gear motor. This type of motor is used because of its good power output (up to 3hp on large table-top models) combined with the capacity for variable-speed control. These two advantages make this aversatile appliance. Read the rest of this entry »
