Exercise Title: Understand the various camera metering modes
Purpose: Now that you have learnt about looking at light and having a good stab at what the settings of ISO, Aperture and Shutter Speed you would need to get a good exposure it is time to look at what the camera does to achieve the same thing.
Working through this exercise will give you a sense of what modes do what and how they affect the resulting image.
Use your manual if you need to and see how you set each of the metering modes on your camera. You should have various options such as spot, partial, centre weighted and average metering. Each of these metering modes look at different portions of the sensor to establish the correct exposure. Each mode still tries to create an optimum exposure they just use different amounts of the viewfinder information to establish it and are all trying to get to 18% grey which is the level of tone shown on a grey balance card.
This mode uses the smallest amount of area in the view finder to establish the exposure and is either the focal point or the centre of the frame depending on your camera. For the purpose of this exercise set the focal point to be the centre of the image, you can move it later to see what happens.
This mode simply extends outwards a little the amount of area used to establish the exposure. Each element of the selected area by the meter is treated with equal importance.
Centre Weighted Metering
This expands the area again, but, gives more bias towards light content at the centre of the image.
This one evaluates the whole frame and considers all parts of the image as equal importance.
Lets start with the last one and work towards spot metering so set your camera to average metering. Either find a scene or create one which has deep shadows and bright highlights in the same scene. For my examples I have just used a black USB stick on a white and black background.
Set your camera to program aperture priority and ensure that any exposure compensation is set to zero.
Either find a scene with areas of bright and dark that you can keep roughly in the centre of the image or create something. For my own tests when doing this I just used black and white card put side by side.
You are now ready to take images:
For each mode you need to take two images. First with the darkest part of the scene over the central part of the image and the second with the lightest part over the centre of the image. You will end up with eight images in total to analyse.
What effect did changing the various modes make to the cameras interpretation of the correct exposure. You will most likely have found that centre, partial and average did not have any extreme effects, however, you should find spot mode was quite significant.
Generally for my own work if I am letting the camera judge the exposure then I stick with centrally weighted as I find that this suits my subject and style. However, if I have something where the light on a specific part of an image is crucial then I know I can switch to spot metering. You can then use the camera to take the reading and set the camera manually.
As an example I put a lens cap onto a white background and a black background then took images at central weighted and spot metering. The results were.
Oops, sorry, it’s been a long time since I’ve not had spot metering on a camera so made the mistake of assuming yours would have it. You are quite right, that is why you would not have seen a great deal of difference. That said though, it was still a useful exercise so you do get to see how your camera does handle it. The more we know our cameras strengths and limitations the easier it is to create images that match our intent.