Unit 25 Exposure meters
Exposure meters
An exposure meter is a device that is used to measure the amount of light to determine a proper exposure. The earliest light meters were called extinction meters and they contained a numbered or lettered row that has natural density filters. This means that when the photographer would meter his subject the filter with the greatest density would still allow incident light to pass through.
The letter or number (whatever type of row that you had) would correspond to the filter and this was used as an index into a chart of aperture and shutter speed combinations for a given film speed aka ISO. The only bad thing that occurred with the extinction meters was that they were heavily dependent on the light sensitivity of the human eye, this was bad because this can vary person to person.
There are two general types of light meters which are reflected light and incident light. Reflected light meters measure the light that is reflected by the scene to be photographed. They are calibrated to show the appropriate exposure for the average scene. If an unusual scene with specular highlights or preponderance of light colours appeared this would have a higher reflectance. Making the light meter reading incorrect. Which means the reflective light meter would wrongly compensate and lead to underexposure.
Incident light meters measure the amount of light which falls on the subject using a intergrating sphere placed on top of the light sensor. The incident ligt reading is independant of the subjects reflectance. Although it is less likely to lead to an incorrect exposure for subjects with unusual average reflectance. Taking a incident light reading requires you to place the meter at the subject's position and pointing it in the general direction of the camera. Which is something that is not usually achieved.
An exposure meter is a device that is used to measure the amount of light to determine a proper exposure. The earliest light meters were called extinction meters and they contained a numbered or lettered row that has natural density filters. This means that when the photographer would meter his subject the filter with the greatest density would still allow incident light to pass through.
The letter or number (whatever type of row that you had) would correspond to the filter and this was used as an index into a chart of aperture and shutter speed combinations for a given film speed aka ISO. The only bad thing that occurred with the extinction meters was that they were heavily dependent on the light sensitivity of the human eye, this was bad because this can vary person to person.
Incident light meters measure the amount of light which falls on the subject using a intergrating sphere placed on top of the light sensor. The incident ligt reading is independant of the subjects reflectance. Although it is less likely to lead to an incorrect exposure for subjects with unusual average reflectance. Taking a incident light reading requires you to place the meter at the subject's position and pointing it in the general direction of the camera. Which is something that is not usually achieved.
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