Get the Perfect Blue: Guide to Underwater Photo Meter

Every digital camera has a built in photo meter. The photo meter takes a reading of the light in any setting and calculates the best exposure settings based on those readings. If you are using manual mode, you will need to manually adjust the exposure settings based on the meter reading that is displayed on your LCD display or viewfinder. Most digital cameras have three meter modes that effect how the camera chooses the best exposure settings. These modes are matrix metering, center weighted metering and spot metering.

Matrix Metering

In this mode, your digital camera will split a scene up into a matrix and take a light reading based on each individual segment. Matrix metering is not the best choice if you are taking underwater shots using a wide angle lens. Matrix metering tends to work at its best when there isn't an extreme dynamic range of brightness levels. When you are underwater, there tends to be bright light blue towards the surface and dark deep blues at deeper depths. The algorithms used for matrix metering will have a very difficult time reading the extreme lights that are present underwater. If you tried to shoot a subject that is already bright using a wide angle lens and matrix metering, the subject will most likely be overexposed because the camera will try to overcompensate for the dark blues towards the bottom of the image. If you are shooting in an area where the colors are more balanced, you can use matrix metering without worry.

Center Weighted Metering

Center weighted metering is a much better option for underwater photography where a wide angle lens is being used. This method of metering takes an average light reading of the entire scene. By using center weighted metering, the camera will be less likely to overexpose a scene due to a bright spot or different shades of blue because this mode of metering is taking the brightness levels of the entire scene into account. The downside of this method of metering is that you have to tell the camera which area you want properly exposed. If the center of your image is a white shark or bright sun, center weighted metering will incorrectly expose the image area outside of the subject. 

Spot Metering

If you want the most control over your exposure reading, then spot metering is the way to go. This method of metering bases almost the entire reading off of a very small part of the scene, typically the center of the frame. This method of metering is not for beginners, as you need to know the best place to meter. Spot metering is very helpful in scenes with high contrast. If there is sun or different shades of blue in your scene, you will want to purposely underexpose the subject you are shooting in order to receive the correct lighting. If you are not familiar with this method of metering or if you do not need selective exposure, it is recommended that you stick to center weighted metering for the perfect blue.

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