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UER Forum > Archived UE Encyclopedia > Light meter (Viewed 72 times) EvilSpork  Location: Miami, FL Gender: Male Behold the power of cheese!  |  |  |  Light meter < on 1/24/2004 4:05 AM >   A light meter is used along with a camera to measure the amount of light being reflected by a scene, and the proper exposure values for photographing it. Remember, no light meter is perfect, and how your light meter sees a scene is not necessarily the way you want it to come out. Use the Bracketing technique whenever you're unsure of the proper exposure (or just don't want to risk messing up a particularly cool picture). There are different types of meters; some are housed inside a camera, usually an SLR Camera, and others are seperate handheld units. Metering can be done by several different methods. On some film and digital cameras with a builtin meter, you have a choice over which one is used. Matrix metering: Exposure readings are taken from different points across the scene, and automatically computed to determine the proper exposure. Average metering: The reading is taken across the entire scene. Spot metering: The exposure reading is taken from one spot, usually indicated as the circle in the center of a SLR Camera's viewfinder. Center-weighted metering: Like spot metering at the center of the scene, but with a larger area. In an average scene, you want your meter to measure the light level reflected from an area of approximately 18% gray, under the same lighting as your subject This may seem a bit confusing to you until you get the hang of it. This 18% gray does not necessarily need to be gray; it is only a reflectivity value. Fortunately, this approximate 18% gray is provided to you free of charge by a material you will find a lot throughout your explorations: concrete. The surface you aim your meter at does not necessarily have to be gray, either; it only has to be at about the same value as 18% gray. Each method of metering has its advantages and disadvantages that should be considered when setting up to take a photograph. Spot and center-weighted metering are the most likely systems to be found on a manual camera. Look through the viewfinder and you will see a mark at the center. This will either be a circular spot (which may include a split-image [rangefinder]) or a mark that looks like a pair of parentheses: ( ). This is the area in which metering will take place. The metering area should be aimed at an area of approximately 18% gray while measuring the light level. Spot and center-weighted metering will ignore the light levels present outside the metering area. Average metering is a bit trickier to handle. Some older cameras (such as the Canonet 28) and light meters use this method. Average metering, in its simplest form, is just the light from an area roughly the size of your photograph being focused on a single sensor. This can easily be fooled into displaying a high value by bright spots, leading to an underexposed photograph. Matrix metering is probably the best method for use in point and shoot or other completely automatic exposure systems. It uses multiple sensors to determine the light level in different areas, while usually giving some priority to the center, and preventing a single bright area from screwing up the exposure reading for the entire frame. The light meter will either be integrated into the controls of your camera somehow, or will be seperate, with a slide rule-type calculator for the proper exposure values. Make sure the light meter is set to the proper speed to match the film you are using. On newer automatic cameras, this will be automatically done when the camera reads the DX code on the film canister. The readout on a meter built into a camera will be any of a few different kinds of indicator. It may either be three LEDs (+, 0, -), an LED readout with multiple bars, or a meter needle that moves inside the viewfinder. The camera's meter is usually coupled to the f-stop and shutter speed currently set to indicate whether they are within range. A handheld light meter will have its own slide rule calculator on it to indicate the proper exposure values. This usually works by setting the film speed on the circular slide rule, then rotating it to match the needle position. When buying an older camera or light meter, there are a couple of things to watch out for. Light meters basically fall into either of two design categories. One is based on a selenium cell, which is basically a photovoltaic solar cell. The advantage of this system is that it does not require a battery to operate. Unfortunately, selenium cells degrade over time with constant exposure to light and humidity, and will cause the meter to go out of calibration or not respond to incoming light at all. A selenium cell can be identified as either a large flat glass plate that appears to have a grayish-red or gray coating on the back, or some object behind a cover that looks like bubble-wrap. If you are going to buy a camera or meter with a selenium cell, check its calibration against a known working light meter first, and keep it stored in a dark, dry place when not in use. Other meters use a CdS (cadmium sulfide) cell or photodiode as a sensor, requiring a battery as a power source. Often, on older equipment, this meter is calibrated for use with the voltage of a mercury battery, which may be unavailable or difficult to find (and will become more so as time goes on). Check to see if the equipment is capable of running on (or easily converted to operation on) a lithium, alkaline, or silver oxide cell, which are all currently in production. An alternative to the mercury battery for equipment which requires the voltage of a mercury battery is the Wien cell, based on zinc-air chemistry. Mmmm... the sweet smell of damp concrete. <3 UER Forum > Archived UE Encyclopedia > Light meter (Viewed 72 times) All content and images copyright © 2002-2024 UER.CA and respective creators. Graphical Design by Crossfire. To contact webmaster, or click to email with problems or other questions about this site: UER CONTACT View Terms of Service | View Privacy Policy | Server colocation provided by Beanfield This page was generated for you in 78 milliseconds. Since June 23, 2002, a total of 738778571 pages have been generated.