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Metering the scenes exposure determines the right combination of shutter speed, aperture, and ISO.

Photographing butterflies at Franklin Park Conservatory in March.
Photographing butterflies at Franklin Park Conservatory in March.
Photo by Bill McCracken


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The image of the butterfly is a good example of metering with mixed light. The difference here is in the colors with the background being mostly green and the butterfly color brown. Metering on the butterfly makes this area 18% gray.  But the background becomes brighter than the subject leaving it dark.

The camera meter is a reflective meter and it sees the colors between black and white as 18% gray. Measuring reflected light from the subject could cause problems because if the subject is predominantly white the meter sees it as 18% gray and sets the exposure to low producing a dark image. The opposite happens when the subject is predominantly dark in color.

Two metering choices are available, manual or auto. Choosing the spot meter in manual mode allows the photographer to choose where the meter reading is taken. When there are large bright areas in the image spot metering allows you to select the reflective surface to meter. Ignore the light areas and produce the correct exposure on the subject.

The auto program mode will allow the camera to pick the correct overall combination. However pattern, and matrix metering can be affected by values outside of the subject. Any exposure plus or minus 2 ½ stops in the image will cause them to be all white or black. These two metering modes will also average between the readings.

In this case the brown butterfly and the green background are close in tonal value. Pattern metering produced a good background but a darker butterfly. As a result the available light was to low for an acceptable shutter speed. TTL flash was added to fill in light on the butterfly and under the leaf. Adding the TTL flash to the image affected only the subject close to the camera and the background stayed the same. Please refer to “light balancing in nature photography”.

The compact camera also has the backlight mode that in this case would compensate for the background being bright and the darker butterfly. The flash will automatically fire when the values are more than a stop.

The butterfly exposure is shutter speed 1/60 sec, aperture f/11.0, ISO 100, White balance flash, and pattern metering.

 

http://www.slideshare.net/Mr_Pixel/reflective-metering-primer

 

http://www.scantips.com/d300/sb800.html

 

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