There are numerous detection devices available and choosing the right one to protect a particular area isn’t always easy. There is a whole range of circumstances to take into account — the size of the room, what’s in it, even how it is constructed, as well as what’s outside or even across the road.
You may need one or more types of detectors in any one area — for example, there are bound to be doors and windows to protect as well as the room itself. There may also be very large areas of glass, such as a patio door, draughts or heating, which may make it difficult to site certain types of detectors, and you may have pets in the house which will mean careful positioning and directing of the detection pattern. 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 »
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 »
A focusing screen provides a flat surface on which an image can be precisely focused and allows the eye to see the whole image at once for framing and composing. It normally comprises a ground glass screen, a fresnel lens and one or more focusing aids.
A ground glass screen scatters light in all directions allowing the whole image to be seen, but the picture you see is brighter in the centre. Coarse etching of the glass reduces this. A fresnel lens comprises a series of stepped, concentric rings. Read the rest of this entry »
