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 »
Exposure meters indicate light intensity and are designed to help you get a correct exposure every time you take a photograph. When a light reading is taken the meter indicates the correct adjustments needed to the camera aperture and shutter speed settings. This sounds simple, as indeed it is, but not all subjects can be treated in a straightforward way. How would you tackle a backlit subject, a snow scene or subjects in deep shadow, for example? In such situations your exposure meter can well mislead you into giving the wrong exposure. ‘Correct‘ exposures are a matter of interpreting meter readings and applying them to the subject in hand. 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 »
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 »
All the mains appliances featured here have some kind of mains cable. Problems with the electronic cables of portable appliances are quite common, especially those that are moved around constantly while in use, such as vacuum cleaners and hedge cutters.
The problems can range from a simple break in one or more of the conductors, which would render the appliance open circuit, to the breakdown of the cable’s insulating properties caused by damage, fatigue or neglect, leading to the risk of electric shock or fire. Electronic cables and extension leads must be checked regularly and thoroughly.
There are several different types of flexible electronic cable in two-core and three-core configurations on the appliances shown here. It is important to remember that two-core electronic cable is used only on double insulated appliances; three-core electronic cable is used on all items requiring an earth connection. Read the rest of this entry »
The term ‘harness‘ is used for all of the wires that connect the various components within an appliance. In large appliances they are usually bound or fastened ‘together in bunches to keep the wiring neat and safely anchored. Smaller appliances, however, may sacrifice neatness for safety and route the wiring to avoid contact with heat or sharp edges. The correct positioning of wiring also contributes to the double insulation of an appliance, so no alterations whatsoever should be made to the routing or position of the wiring in double insulated appliances.
When you first take a look at it, the harness may seem like a jumble of wires thrown together, but if you take the time to inspect it, you will find that each wire is colour-coded or numbered either on the wire itself or on the connector at each end. This allows the engineer to follow the wire through the appliance easily. With a little practice, any wiring or coding can be easily followed. 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 »
Whether cheap and simple or astronomically expensive, all decks are averse to dirt and debris which is statically attracted to the vinyl record. It then damages the stylus resulting in the all-too-familiar click, pop and jumping of the track.
Sound is stored on a vinyl record on a continuous groove starting at the outer edge and finishing at the centre of the disc. The groove has microscopic ridges proportional in size to the sound wave that created them. When the record rotates, the stylus is deflected by these ridges as it runs in the groove. These minute deflections are then amplified. Two requirements must be met for the stylus to track correctly. The first is that the groove of the record is free from all blemishes and foreign matter to which the stylus would react. The other is that the arm holding the stylus must apply just enough weight to hold the point within the groove (usually 1-2 grams) but not so much as to create excessive wearing of the groove. Read the rest of this entry »
Three main types of domestic, free-standing, portable electric heaters are widely used: radiant, convector and fan heaters. Some appliances combine different heater types, such as a convector plus a radiant bar.
Heat is produced by an element that glows red-hot when power is supplied to it. The heat generated by this action is directed by a highly polished reflector through an open front protected by a metal grill. The element can be externally wound on a ceramic mount or internally mounted in a heat-resistant silica glass tube. Simple switching of the element/s is included and faults can easily be traced. Read the rest of this entry »
