Metering Modes

In order to produce an image that is not too bright (overexposed) or too dark (underexposed), all digital cameras need a way to access accurately how much light is present in the scene that is being photographed. Now cameras have built-in light meters that measure the light reflected from the subject or from the scene as a whole. The problem for the photographer is that the brightness can vary significantly from one part of the image to the next. For example, the sky is far brighter than the land during sunrise or sunset. If you were to set the exposure manually, the area you should set the exposure for depends on the result you want; normally you would set the exposure for somewhere between the two extemes. The way a camera arrives at this compromise depends on the type of metering system it uses.

How the camera measures light:

The exact method that different cameras use to measure exposure varies from model to model - but essentially there are three types of metering system commonly found on modern cameras. Three modes present in Sony Cybershot DSC-H2 are

1. Centre - weighted metering:

In this mode, the metering is biased or weighted to the centre of the view-finder (three boxes shown in the picture) and then averaged for the entire scene. This mode is very useful when taking portrait shots.

2. Spot Metering:

Spot metering in most cameras takes a reading from the very centre spot (black dot shown in picture) of the viewfinder (In Sony Cybershot it has flexibility to move this spot) and sets an accurate exposure for that part of the image only. This metering mode should be used when the subject is correctly exposed, no matter how much (or how little) light is falling on the surrounding areas, or during close-up photography.

In the above picture spot metering was used and a part of this picture was overexposed.

Both these pictures were shot at same time and I used spot metering mode for both but position of the spot was different. Spot was on the sky for the picture on left and it was on the bird for the picture on right.

3. Multi / Matrix metering:

This is most sophisticated of all the metering systems, and is the 'default' mode for the most cameras that offer metering option. It works by taking multiple readings from from various points in the scene, while also assessing the position of the main subject, foreground and back-ground, overall brightness, any front - or backlighting, colour and so on. The camera then compares these readings with a database of thousands of 'typical' photographic scenes and selects the exposure that most closely resembles one in its database.

My experience on Metering:

• Pick the "Center-Weighted Metering" mode when you want the camera to meter the light in a broader area than with spot metering but not the entire frame. With center-weighted metering, you can focus on a larger portion of your frame. This is a good option when you’re taking group photos or portraits.

• Select the "Spot Metering" mode when you have one small subject from which you want to record the light value. Spot metering is handy when your subject is in front of a bright background, such as a sunset. By choosing to spot meter the light from the subject only, your camera will adjust the settings, making your subject visible as opposed to creating a silhouette.

• Choose the "Multi Metering" mode (multi-segment metering) for a good all-around photo. In most digital cameras, this is the default meter setting and it measures the light reflected in all parts of the frame and uses the combination to select the light value. For most purposes, matrix metering is sufficient.
  

Next I will discuss about Histogram

Modes of Shooting in Digital Camera

All digital cameras, either point and shoot, compact or dSLR have a variety of auto or preset shooting modes. These modes are usually (as in Sony Cybershot and Olympus)

• Auto
• Close up / Macro
• Portrait
• Landscape
• Action
• Night
• Panorama
• Program (P)
• Shutter Priority (S)/Time Value (Tv)
• Aperture Priority(A)/Aperture value(Av)
  
  

Auto:
As the name suggests, in Auto mode everything is automatic, with camera taking complete control of all the settings. It will set the ISO, white balance and focusing mode, etc. etc.. This mode is often used by beginners or new users as it almost guarantees a correctly exposed and sharp image.

Close-up / Macro:

The Close-up or Macro mode is used to take close-up pictures of small subjects. The depth of field is very narrow in this case. However if you want the entire subject to be in focus you shuould shoot from directly above or directly below the subject so as the much of the subject as possible is at the same distance from the lens.

Portrait: In this mode the camera will set the largest possible aperture to create a narrow depth of field.This throws the back-ground out of focus so that more empasis is placed on the subjects face.

Landscape:

This mode works on the oppsite way to Portrait.The camera will set the smallest possible aperture to create the widest possible depth of field.This ensures that as much of the scene(and ideally from foreground to background)is in focus.

Action:

When photographing any fast moving sport or action scene.The camera will automatically select the fastest poosible shutter speed (depending on the available light) in order to freeze the action.You'll usually have better success if you follow the subject through the lens for a few seconds before taking the shot.

Night:

The night mode is designed to take portrait photographs in low light.The camera will set a relatively long shutter speed to ensure that the dark background is capturedwhile firing the flash to light and freeze the subject.This is known as "slow sync".You should always make sure that your subject remains still even after the flash has fired as the camera may still be recording.

Panorama:

In this mode,after the first image is taken the exposure and white balance are "locked" so that all subsequent images have the same colouration,tone, contrast.You then take the next picture and align the image with the previous one, of which about a third appears semi-transparent on the LCD screen.

Program (P):
Selecting P will allow you to change the ISO setting, image size and quality,the metering mode and a number of other settings that are set automatically when the camera in the auto mode. Detail about ISO settings was discussed in my previous blog on ISO, sensitivity and noise in digital camera.

Shutter Priority (S)/Time Value (Tv):

In this mode you can set a specific shutter speed( fast to freeze action or slow to deliberately blur objects).The camera will set an appropriate aperture depending on the available light. Above picture was taken with slow shutter speed to give blurry effect to water fountain.

Two pictures are shooted with different aperture speed to show aperture speed's effect on the flowing water. Picture on left is taken with shutter speed =1/4 sec. Picture on right is shooted with shutter speed = 1/500 sec.

Aperture Priority(A)/Aperture value(Av):

This mode works in similar way to (S)/(Tv) mode but the opposite way around. You can set a larger aperture to throw background out of focus or set a small aperture to increse the depth of field (to ensure a landscape is in focus from foreground to background).The camera will automatically select an appropriate shutter speed .

Picture on left is taken with larger aperture (Fstop = f/5.6) and on right is with smaller aperture (Fstop = f/22). You can observe how the background changes with the change in aperture.

Next I will discuss about the metering modes and histograms.