exposure and light meters
Taking a hand-held meter reading Incident reading For an incident reading it is important to place the white plastic dome supplied with the meter over the light-sensitive cell. This is called an ‘invercone’. The purpose of the invercone is to diffuse the light falling on the subject from a wide angle of acceptance (180°) and transmit 18% of that light. The sensitivity or ISO of the digital image sensor must then be calibrated into the meter. The light meter is generally taken to the subject and the light-sensitive cell is directed back towards the camera. The reading may default to EV (exposure value) which can be interpreted or changed to an aperture/shutter speed combination. On modern digital meters the photographer is able to pre-select a particular shutter speed or aperture and have the meter indicate the corresponding value to obtain correct exposure.
Creating an incident reading using the camera’s TTL meter You can place a diffuser such as the ‘expodisc’ over a camera lens in order to create an incident light meter reading using the camera’s own TTL meter. This type of product is also excellent at creating a custom white balance setting or can be used to capture a reference image that can be used to create a white balance setting in Adobe Camera Raw.
Activity 4 Take an incident light reading of a subject in a constant light source. Note the f-stop at an exposure time of 1/8 second. Increase the number of the aperture by three f-stops. Note the change in exposure time. What would the result be if the duration of time had been increased by a factor of three instead of the aperture?
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