How to combine evaluative and spot metering

As photographers, we are presented with many different lighting situations and must learn to expose our scene based on our interpretation of the subject, lighting and the look we are trying to achieve. To help us, cameras have three metering modes.

• Evaluative / Matrix metering.
• Centre-weighted metering.
• Spot-metering.

But did you know that you can combine Evaluative/Matrix metering (E/M)with spot-metering (SPm) to help ensure that the most critical parts of your scene or subject are exposed correctly? You also need to switch to manual mode so that you can access your camera’s inbuilt light meter.

Before getting into the detail here is the basic process.

1. Switch your camera to manual mode.
2. If your camera has a live histogram turn it on.
3. set a base exposure by zeroing your camera meter.
4. Using your histogram check the light distribution.
5. Switch to spot metering to check the luminance levels of the key parts of your scene or subject.
6. Adjust exposure as necessary.

Manual mode

You need to be in manual mode to see your camera’s light meter and control the aperture, shutter speed and ISO. With practice and experience, you will find that working in manual mode is actually very easy and gives you precise control over your exposure. My basic way of working is to choose my working ISO, set my preferred aperture and then control my exposure by adjusting my shutter speed. As you have already decided on your ISO and aperture settings all you need to work with is adjusting your shutter speed to obtain the optimum exposure for your subject or scene.

Histogram / Spot meter

Once you have zeroed out your meter use your histogram as a visual reference to see the distribution of light and whether or not you have any highlights or shadows clipped. Now switch your camera to spot-metering mode.

Spot metering Midtone, Highlights & Shadows

With your camera set to spot metering mode, you can now meter the most important parts of your scene and check how bright or dark things will look or if your subject is going to render as a midtone. as an example, the image below was captured with natural window light, it is a contrasty image with not many midtones and made up of mostly dark tones, our histogram shows us this. Knowing that my scene was prominently made up of dark tones I reduced my exposure until my histogram was pushed to the left but not touching the left side of the histogram. However, my histogram does not show me how the most important elements in my image will render! In other words, will I be able to see the detail in the dog’s black coat or will it be purely black? And what about the part of the dog’s coat that is white, will detail be retained there and will it come out looking brighter than a midtone? I cannot know this unless I take spot readings based on my exposure to see the difference in stops between my base exposure and the most important highlight and shadow detail in my image, in this example, the dogs’ hair. When I did this, I could see that the most important shadows were -2 stops and the most important highlight +2 stops.

With this information, I now know my most important subject the dog will be exposed correctly. If the spot meter reading for the dog’s black hair had been more than -2 stops it would have rendered black with little or no detail in the hair and the inverse for the white hair more than +2 stops and I would have little or no detail in the white hair of the dog’s coat.

Exposure compensation based on combined readings

Now that we know how to set a base exposure using evaluative metering and how to check our subject’s most important highlight, shadow and midtone areas, we can make some informed decisions on how best to optimise our exposure!

Once you have your base exposure and you have checked how your most important tones will render, you can use adjust your exposure to favour the most important part of your subject. As an example, if after setting my base exposure the dog’s white hair had been +3stops, I could have increased my shutter speed from 1/125s to 1/250s to ensure that the dog’s hair would render properly. Naturally, when you do this the other tones shift too. However, the idea is to optimise your exposure for your subject.

By working this way you have full control over exposure and how your subject will render.