A photography concept that is quite easy to understand yet perceived as a complicated one is of Metering. It is very important for any photographer, amateur or professional or even someone who has taken up photography as a hobby, to understand what metering is and how it works in order to be able to take better pictures. Lets understand What is metering in DSLR and how it works?
WHAT IS METERING?
Think of it as a small computer inside your camera that evaluates what aperture and shutter speed should be used for a particular picture. When you take pictures in Auto mode, you leave it for the camera to decide the correct exposure and just press click however when you shoot in manual mode, you have to decide for yourself what aperture and shutter speed you want to use. In auto mode, the camera meter will do the job without you having to worry about aperture or shutter speed. In manual modes however, camera’s metering system will tell you in if the selected setting is correct or not and if the image would either come out over-exposed or under-exposed. Metering is how your camera determines what the correct shutter speed and aperture should be, depending on the amount of light that goes into the camera and the sensitivity of the sensor.
HOW METERING WORKS?
Light meters fall in 2 categories, Internal and external. Internal light meters are the ones built inside your camera and the external ones are more of an accessory that you buy with your photography kit. Ever seen a photography holding a gadget out in the sun or air and taking the readings? That is an external light meter that he is using to determine the exposure he should use.
Internal light meters are based on reflected light which means that they determine the exposure based on the light that is reflecting off the subject. External light meters however make this decision based on the light that is falling on the subject, known as incident light.
Your camera meter will work great if the scene is lit evenly however problem arises when light is distributed at different levels. Assume that you are taking picture of blue sky with no sun then your image will be correctly exposed because it is the same light level in the entire frame. However If you add clouds to the same scene, it gets challenging for the camera meter to determine the optimal exposure while evaluating the brightness of the sky verses the brightness of the clouds. To correct this, the camera meter would either brighten up the sky a little bit or darken the clouds to keep the light levels even. If you add a mountain to the same scene, the camera meter would sense a large and dark object in the frame and would try to come up with something in the middle, so that the mountain is properly exposed as well. By default, the camera meter looks at the light levels in the entire frame and tries to come up with an exposure that balances the bright and the dark areas of the image.
DIFFERENT METERING MODES
All modern day DSLR cameras come equipped with an option to change the metering mode. There are 3 type of metering modes available:
1. Matrix Metering (Nikon), also known as Evaluative Metering (Canon)
2. Center-weighted Metering
3. Spot Metering (Nikon), also known as Partial Metering (Canon)
1. Matrix Metering: This is the default metering mode on most DSLRs. It works by dividing the entire frame into multiple “zones”. The camera meter then takes readings from all zones, analyzes them and determines the best exposure after averaging it out. Some of the key factors that affect matrix metering are color, distance, subjects, highlights, and camera’s focus point. There are some other factors as well depending on the manufactures. Nikon for example also makes a comparison to an image database of almost 30,000 pictures to calculate correct exposure. This is also the most widely used metering mode as it does a pretty good job in most of the situations. You should leave your camera with Matrix Metering selected for most of your shoots.
2. Center Weighted Metering : This setting comes in handy when you want to want the camera meter to evaluate light from the center of the frame and ignore the rest. In this setting, the meter will give importance to the light that is concentrated in center of the frame. This setting comes very handy in portrait photography or close-ups. For example, If you were to take a head-shot of a person with Sun behind him or her. However in Center weighted Metering, camera will also ignore your focus point and will only analyze the light in middle area of the image.
3. Spot Metering: In this setting, the camera meter will evaluate light only around your focus point and ignore the rest. It analyzes a single zone and calculates exposure based on that single area. Use this setting when there is a high contrast in the picture, If there is a chance of your subject falling into shadow, Or if your subject isn’t taking much of space in the frame. Another example of using spot metering will be while photographing the moon because the moon will only take up a small portion of the frame while the rest will be filled with completely dark sky.
