Friday, 6 September 2013

Understanding Reciprocity in Photography

Today's article from Picture Correct is written by Keith Trigwell, a live music photographer who also has a passionate interest in most other types of photography, particularly portraiture and Fine Art. It is aimed to help you understand the relationship between shutter speed and aperture, and then how you can utilize ISO to further hone your settings

Perfect exposure settings: Reciprocity is the law of the relationship between shutter and aperture. It stipulates that one stop increase in aperture is equivalent to the shutter duration doubling. Both increase light by one stop.

Thus, once you have the correct level of light for perfect exposure you can choose to increase aperture by one stop and trade this off with a doubling of the shutter speed (halving of the shutter duration). Twice as much light coming in for half the time = same amount of light.

This allows the photographer to retain the same exposure but change either aperture or shutter for artistic or practical reasons.

In addition to this the photographer may wish to over expose or under expose. Understanding the law of reciprocity allows them to do this in a controlled and intuitive manner, understanding the exposure differences on the image PLUS the different changes to the depth of field or any motion blur increase or decrease.

Sometimes however, the aperture you want and the shutter speed required do not give an adequate exposure with the available light (either natural or including flash). Fortunately there is another variable which effects exposure with the same degree of effect and working in the same measurements of stops of light.This is ISO and refers merely to the cameras sensor’s sensitivity to light.

You therefore have THREE variables at your disposal. Each however alter the image beyond just the brightness of the final image.

Follow the link to read the full article:  Understanding Reciprocity in Photography – PictureCorrect

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