Thinking about exposure

Recently, I was told I should expose to the right (ETTR) when using a micro four-thirds camera (M43). The idea behind ETTR is to overexpose your image so that you open up the shadows without blowing out your highlights (wherever achievable) to give you as much data as possible to work with when processing your RAW files (ETTR is not recommended when shooting JPEG).

Below is the image where it was suggested that I use ETTR.

We see the world in colour but every object in our scene has a brightness value ranging from pure black to pure white.

If you look at the black and white image of the cat and the histogram you can see that there are no bright or white tones except for the specular highlights in the cat’s eyes.

Rather than exposing to the right (ETTR) as suggested, I based my exposure on the left side of the cat’s face and checking the histogram I could see that my shadows were not blocked out and that there were no highlights to worry about (bright areas in my scene), the histogram shows me that I have plenty of data to work with when post-processing my image.

My point is that before you press your shutter button you need to assess the tonality of the scene or subject you are shooting and make intelligent decisions on how to expose your image, relying on ETTR is not suitable for all situations and should not be overused, it is just one way of capturing a scene.

Let’s talk about metering

When you look at a scene or subject it has an overall brightness and a contrast range depending on the quality of light and the reflective properties of the elements within your scene.

There are basically two methods for taking light (metering) readings, incident light metering or reflective light metering.

Essential point: If you photograph a black vase and a white vase together under the same lighting conditions then they should both need the same exposure!

• If you use an incident light meter and measure the light falling on the two vases you will get an exposure based on the intensity of the light illuminating your subject, and the exposure will be correct for both the black and white vases.
• If you take a reflected light reading from the black vase it will come out lighter in your final image (not black more grey) and the white vase will be overexposed! if you take a reflected light reading from the white vase it will come out darker (not white more grey) in the final image and the black vase will be underexpsoed, why? Because reflected light meters measure the intensity of the light rebounding from the subject and the intensity of this light varies depending on the reflective properties of your subject, taking a light reading from the white vase or the black vase means that your exposure will render the vases as a mid-tone (grey) and your vases will not look as they should.

Why does this happen? All light meters whether an incident or reflective light meter render your subject as a mid-tone or middle grey. Understanding the concept of mid-tone or middle grey is important in obtaining the correct exposure for your subject. It is commonly referred to as 18% grey or zone V.

All scenes or subjects are generally made up of a number of light or dark tones. Compare the two images below. Because we see the world in colour, it is not always to imagine what a scene looks like in various shades from black to white. But this is exactly what we need to do when analysing a subject or scene.

The concept of the zone system helps us out here. Compare the black and white image and the grey-scale values opposite, you can see that our image is made up of a number of values from the greyscale, ranging from zone 2/3 all the way to zone 8/9.

When we photograph a subject or scene we want to be sure that our tones fall into the right place to render our subject correctly. Every time we use our camera meter or a handheld reflected light meter to meter a scene or subject it is always rendered as a midtone, it is up to us as photographers to decide whether the resulting exposure is correct for our subject.

If our subject is a mid-tone (middle grey/zone V) then it will be exposed correctly, if it is not, then we have to ask ourselves how much lighter or darker than the mid-tone is our subject and bias our exposure accordingly.

The zone system was developed for film use, it can still help digital photographers ensure that they get the correct exposure for their subject, each zone is equal to 1 stop. In the example of the white and black vase, if we take a reflected light reading from the white vase we know that it is not a mid-tone, its much brighter than that, which means we would have to apply at least two stops of exposure compensation to render it white (open up two stops). The opposite is true if we meter from the black vase, we need to stop down two stops for it to render correctly.

You don’t need to remember the zone system or learn too much about it, you just have to realise that if your subject is not a mid-tone you will need to apply some exposure compensation.

I simply ask myself when shooting, is my main subject bright, brighter or brightest? Or if its a dark subject, is it dark, darker or darkest and then set my exposure accordingly

Dark subjects	Dark	Darker	Darkest
Zone	4	3	2
Stops	-1	-2	-3

Applying the principles above to your photography

To use the above you would need to work with a spot meter and use your camera in manual mode. I prefer using a handheld meter but you can use your camera’s spot meter if you have one. The key thing about working this way is that you are controlling how light or dark your main subject is by placing your subject in the appropriate zone. Setting your exposure based on the brightness of your main subject also influences how bright or dark other objects in your scene render.

More on metering

We have said that there are two main types of metering, incident and reflective.

Hand-held meters

Incident light metering

Incident light meters read the intensity of light falling on your subject, in other words, they ignore the reflective properties of your subject, providing very accurate exposures. All of the issues about how light or dark a subject is go away when using incident light metering. An incident light reading is the most accurate way to meter your subject.

Check out light meters at Wex Photo

Spot meters

Spot meters are expensive and are very precise, they allow you to take single or multiple spot readings, average out your readings and normally allow you to apply exposure compensation too. They are ideal for determining the overall contrast of your scene and for placing your subject in the appropriate zone.

Camera meters reflected light metering

Most modern digital cameras have three metering modes

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

Let’s explore each of these in turn,

Matrix/Evaluative metering

Matrix/Evaluative metering simply means that your camera is taking multiple readings at the same time from the different parts of your scene or subject, measuring the brightness of the scene and then averaging out the readings to give you an exposure value. It is considered to be a fairly accurate way to meter a scene but if your scene or subject is made up of mostly light or dark tones, in other words, there is not a range of tones in your scene from black to white, evaluative metering may not give you the correct exposure. It is not suitable for applying the concepts of the zone system.

Centre-weighted metering

Simply measures whatever is in the centre of your viewfinder, giving less priority to the edges of your scene. Again, it is not suitable for measuring and placing your subject in the correct zone.

Spot-metering

Camera spot meters are not as precise as handheld spot meters but can still be used to make accurate exposures. When I do not have my handheld meter with me I tend to use my camera’s spot meter and switch to manual mode.

Spot metering and Manual mode.

Most cameras have an internal light meter. However, you cannot access it unless you switch to manual mode. It will look something like the image below.

By shooting in manual mode and using spot metering you can begin to measure the different parts of your scene and see where your subject falls in terms of tonality,

Remember, light meters are calibrated to provide you with a midtone reading of your subject, which means that they always return an exposure value equivalent to 18% grey (zone 5 midtone)!

Taking a spot reading using your camera spot meter

When you set your camera to manual mode and point your spot meter at your subject you will get a meter reading, if you change the aperture and shutter speed until you zero out your meter (as above) you will have set your exposure to provide a midtone reading or an average reading. If your subject is a midtone or close to midetone the exposure for your subject will be correct. If your subject is not a midetone then you need to adjust your exposure to match your subject.

Changing exposure to match your subject

subjects darker or lighter than a midtone

For subjects that are darker than a midtone we need to reduce exposure (stop down) and for subjects that are brighter, we need to increase exposure (open up).

I simply ask myself, how much brighter or darker is my subject than a midtone and then adjust my exposure accordingly.

• Zone 2 Darkest – just a hint of detail, almost pure black (hardly any details)
• Zone 3 Darker – deepest shadows with some detail, dark fur (think very darkest colours)
• Zone 4 Dark – shadows (think darker colours)
• Zone 5 Midtone – very few subjects fall here but many subjects will be more or less a midtone. (primary / average colours)
• Zone 6 Bright – lighter subjects (think pastel colours)
• Zone 7 Brighter – clouds, white fur
• Zone 8 Brightest – bright snow in sunlight, almost pure white

Rather than zeroing out your meter reading, you need to decide how much lighter or darken your subject needs to be and then adjust your exposure until your meter reading shows that you are under or over-exposed by the correct number of stops.

Learning to assess the dynamic range of a scene and base your exposure on the brightness of your subject will provide you with accurately exposed images and you will spend less time post processing your files.