Exposure compensation with extension tubes and bellows
Exposure compensation with extension tubes and bellows | ||
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Using bellows or extension tubes means that the light has to travel further through the system before it reaches the image sensor. If you are not using TTL metering, perhaps using flash in the studio and assessing exposure with a separate flash meter, then some allowance will need to be made for the reduced amount of light reaching the sensor. A formula used to calculate the compensation factor required is: Compensation Factor = Metered Exposure (M+1)2. For example, for a magnification of 1×: Compensation Factor = Metered Exposure(1+1)2 = 4 This factor means that four times more light is required to give the correct exposure (i.e., two stops). A metered exposure of f/16 would become f/8, for example. Of course, with digital cameras, and their ability to display the exposed image and its associated histogram on the back screen, it is easy to adjust the aperture until you achieve the right exposure, and there is little need for such calculations nowadays. | ||