Whether you shoot on auto every time, the P (program), A (aperture-priority), or S (shutter-priority) settings every time, or have mastered the manual operations of your camera, understanding exposure is key to achieving a quality image. In my mind it’s quicker and easier to control exposure through the manual operations on my camera than when I’m using one of the automatic settings - having greater control to change it quickly when it’s not quite right.
Despite how sophisticated cameras have become, shooting on auto doesn’t always mean the camera’s algorithms will capture a scene or subject exactly how you want it, or see it. As the photographer by taking control, and you telling the camera what to do, your results will be a lot better in most situations.
So, what is exposure?
On a simplistic level, exposure relates to how dark or light your photographs are. This is determined by how much light reaches the camera’s sensor when you press the shutter release button.
The three key controls that determine the amount of light that enters the camera are:
ISO - the sensitivity of the sensor to light
Aperture - the size of the hole (technically known as the diaphragm) that lets the light in through the lens
Shutter speed - how long the camera collects light for
When it comes to capturing an image, there is always a process and series of decisions I make before pressing the shutter. Often this is intuitive or responsive and other times it is thought out and planned (depending on the situation and subject matter being photographed). In either situation, the more knowledgeable you become with your camera, the process becomes faster.
The process, for me, generally starts with choosing the metering mode. This comes from deciding what the main element, or elements, in the scene being photographed are. Making sure these are exposed correctly is key!
My go-to metering mode tends to be spot, allowing me to control the element/area of the image I want to set my exposure from. A feature I love on my Nikon D810 is the highlight-weighted metering option, useful when shooting in uneven light or where the subject is highly lit against a dark background as it offers improved exposure control in the brightest areas of the image.
Matrix metering - calculates an exposure based on everything in the entire frame. Works well when the scene is evenly lit, doesn’t work well where you have high contrast (strong highlight/shadows) or the background is very bright.
Center-weighted metering - still looks at the entire frame but emphasis is placed on what is in the middle of the frame to calculate an accurate exposure; good when the main subject fills the center of the frame.
Spot metering - unlike the other two metering modes it calculates the exposure based on the small area where the focus point is positioned within the frame; good for high contrast or back-lit situations.
The next step involves working with the three exposure controls - the shutter speed, the aperture and the ISO. The dilemma for those starting out with manual capture, is how do you know which control to start with. Using the diagram below, if you can understand the effects that the each of the controls produces, at different settings, this will help you work out which control would be best to select first to get your accurate exposure.
An accurate exposure, is achieved by moving any of the three (or all three) ISO, aperture or shutter settings until the camera’s meter is sitting on the 0 mark (see below), with no + or - values showing. Referred to as the “Exposure Triangle”, the process does become a balancing act between the three controls - moving one, then another, until your metering “needle” sits at the 0 mark, letting you know that based on the lighting your ISO, aperture and shutter combination will produce a good exposure.
The three images above show the effect of changing the shutter speed (only), varying the exposure each time. The left hand image has been overexposed to let more light in, the sky is blowing out and detail is being lost in the foreground rocks. In the middle image the exposure was set at “0”, giving a more tonally balanced image, though could still be improved. The right hand image has been underexposed, reducing the light let in, resulting in a darker image where it becomes difficult to see any details. Images by Kaye Davis
WHICH EXPOSURE CONTROL DO I SET FIRST?
The question of “which control do I set first when getting my exposure” is very much dependent on the subject you are photographing, and the effect you want to achieve with the subject; there is no one right answer.
Based on the lighting conditions I’m photograhing in, I’ll usually set the ISO first - as a guide, if it’s bright, I’ll go with 100 or 125 ISO, if its darker/cloudy I’ll set it anywhere from 400 to 1600 ISO. For a good part of my own work I’m using a tripod (with either the timer or a remote shutter release). Using a tripod also allows me to shoot many of my images on 100 or 125 ISO and with a smaller aperture and/or slower shutter speed. The tripod keeps the camera really steady, meaning I can use a low ISO and slow shutter speed without the fear of camera shake (movement).
For the type of subject matter I often photograph (flowers, still life, landscape) my aperture tends to dictate my second decision. Do I want the subject to be sharp from front to back, or do I want that sharpness to fall off with parts of the subject soft and blurred (shallow depth of field).
If I am wanting everything in the image nice and sharp, from front to back, I’ll use a smaller aperture, such as f11-f13. then set my shutter to produce the final exposure (hitting that 0 mark).
Of note though, is that overall image sharpness does tend to deteriorate when shooting at the extreme aperture ranges of the lens (wide open or very small). So, if I can’t achieve the full sharpness I need at say f8 to f13 a process called photo stacking works well; photographing a subject numerous times, shifting the point of focus slightly each time, then with usually combining the multiple images in Photoshop the resultant image is sharp from front to back.
If I’m wanting a shallow depth of field, where areas of either the foreground, or background, are blurry and soft, I’ll set my aperture to f5.6 or so.
However, if I was shooting a moving subject, my second decision would focus (sorry about the pun) on my choice of shutter speed. For example, photographing water, do I want the water smooth and silky, or sharp and ripply? If I wanted it smooth and silky, I’d be using anywhere between 1/4 sec to 30 secs. Often trying multiple shutter variations to confirm which one was giving me the effect I wanted.
Now that I’ve set both the ISO and aperture, the final step (as it’s not really a decision) comes in achieving an accurate exposure. If I set the aperture it will be the shutter speed I alter until the metering lines up with the 0 mark; likewise if I set the shutter first, it will be the aperture that I need to change to get a accurate exposure.
A FEW THINGS TO PONDER
Getting an accurate exposure is firstly deciding what effect you want in your image, and how this effect is achieved by either the shutter or aperture. The subject matter itself and how you want to portray (communicate something about) that subject will help determine this. Check back on the earlier diagram!
While it is a process of decision making, when it comes to Decision 3, there will be times when no matter what setting you use the meter won’t sit on 0. When this happens, you will likely need to make some compromises, or trade offs. This may mean changing the ISO or the control set in Decision 2. If you are lacking light, consider increasing the ISO (or adding in/finding more light). If you have too much light, try adding a Neutral Density filter onto the lens, reducing the amount of “ambient” light the camera exposure meter is measuring, allowing the use of longer shutter speeds (or wider apertures).
There will also be times when despite the meter sitting at 0, the exposure just doesn’t look right!
To produce a good exposure, with the setting on 0, often relies on having soft even lighting across the whole scene or subject. When photographing in harsh, bright light, the likelihood is that you will have areas of brightness and areas of deep shadows, a very contrasty situation.
Most cameras aren’t equipped to capture such a diverse range of tonal values (known as dynamic range) within one image. My suggestion, would be to consider taking a series of images (preferably using a tripod) changing ONE of the settings (usually done with either the aperture or shutter). This produces a set of images captured at different exposures, called bracketing, where the meter sits above or below (towards the + or -) the 0.
If the image captured with the meter at 0 doesn’t work, often one of the other, slightly under or over exposed images may well give you what you need. If this still doesn’t produce a tonally balanced image, there are post-production techniques you could explore, that enable you to blend the bracketed images into a single image.
This may all seem a bit daunting, but believe me, when you spend time playing and experimenting with the manual settings you will definitely gain better control over your exposures, and start to understand how your camera really works. So go out and have some fun!
Kaye Davis is an Accredited Professional Member of the NZ Institute of Professional Photography, a Grand Master of Photography (NZIPP) and Master of Photography II with the Australian Institute of Professional Photography. An international award winning photographer, judge and educator.