Manual Exposure Mode: A Guide to Setting the Correct Exposure
In photography exposure refers to the brightness of an image.
Modern digital cameras are pretty good at figuring our how to correctly expose an image. Unfortunately they are far from infallible and are often fooled into over or under exposing a scene.
Taking control of exposure ourselves is the key to eliminating mistakes made by our cameras.
In digital photography there are 3 things that impact the exposure of a photograph. ISO, aperture and shutter speed.
ISO refers to a camera sensor’s sensitivity to light. As you increase ISO the sensor becomes more sensitive to light and the image becomes brighter.
The base ISO for most cameras is 100. Doubling the ISO increases the sensitivity of the sensor by 1 stop, effectively doubling the brightness of the image.
The downside of using high ISO (400+) is an increase in digital noise. This is imperfections in the image that give it a grainy effect.
Typically we landscape photographers are looking to achieve maximum image quality and so will generally stick to ISO 100 (or whatever is the lowest for our camera).
The aperture is the opening in a lens through which lights passes in order to reach the camera’s sensor. As you increase the size of the opening more light can pass through and the image becomes brighter.
The size of the aperture is expressed using f-numbers. These typically range from f/2.8 to f/22.
- f/2.8, f/4 – large apertures
- f/5.6, f/8, f/11 – medium apertures
- f/16, f22 – small apertures
Reducing the f-number increases the size of the aperture, increasing the amount of light that can pass through and therefore increasing the brightness of the image.
Diffraction is the phenomenon whereby light is bent as it passes around the edge of an object. In photography this impacts the light that passes close to the lens’s aperture blades as it enters the camera.
Diffraction has a negative impact on image sharpness. Using a smaller aperture increases the proportion of light that is effected impacting image sharpness to a greater degree.
To read more about diffraction read this article about how to Take Sharp Landscape Photographs.
Depth of Field
Photographers typically use aperture to control depth of field. The smaller the aperture the greater the depth of field.
Landscape photographers will typically shoot at f/11 as this provides good depth of field with acceptable levels of diffraction.
Shutter speed refers to the amount of time that the aperture is held open whilst taking a photograph.
As you decrease the shutter speed the aperture is held open for longer allowing more light to pass through. As a result the image will become brighter.
In landscape photography as the ISO and aperture are generally fixed setting the correct exposure often comes down to selecting the appropriate shutter speed.
If you are interested in learning more about the exposure triangle check out this video.
Most cameras have a series of exposure modes that allow us to take control of the exposure to a greater or lesser extent.
- Program Shift (P) – the camera sets both the aperture and shutter speed
- Shutter Priority (S or Tv) – the photographer sets the shutter speed, the camera sets the aperture needed to correctly expose the image
- Aperture Priority (A or Av) – the photographer sets that aperture, the camera sets the shutter speed needed to correctly expose the image
- Manual (M) – the photographer sets both the aperture and shutter speed
P, S and A are sometimes referred to as semi-automatic modes. In each case the camera uses its metering system to determine which settings are required to correctly expose the image.
The metering systems on modern cameras are very sophisticated but they are still easily fooled. This can cause problems when using any of the semi-automatic modes.
These problems are most obvious when photographing scenes that contain a lot of light tones or a lot of dark tones.
If a scene contains a lot of light tones (for example when photographing snow) the camera will be fooled into underexposing the image.
If a scene contains a lot of dark tones (for example when photographing at night) the camera will be fooled into overexposing the image.
As a result I prefer to shoot in manual mode so that I have full control over the exposure of my images.
Shooting in manual mode gives me full control over both aperture and shutter speed.
For some genres of photography, particularly those that require the photographer to react quickly to what is going on around them, the advantages of the semi-automatic modes far outweigh the disadvantages.
But as a landscape photographer I can generally take my time and make sure everything is perfect.
I have to confess that when I first started photography was a little scarred of manual mode. I was worried that I would get the settings wrong and miss the shot.
However, the introduction of live view made everything much easier.
For me the introduction of live view was the biggest advancement in photography since I started back in 2006.
It has completely changed how I take photographs. I use it for composition and focusing as well as setting the exposure.
The live view on my Canon EOS 6D has 2 features that make shooting in manual mode far easier than it once was. Those are the histogram and exposure simulation.
A histogram is a graphical representation of all of the tones in an image. It allows you to determine the number of dark pixels in relation to the number of light pixels.
If the histogram shows that an image has lots of dark pixels there is a chance that the image will be under exposed. It it shows that it has lots of light pixels then it could be that the image is over exposed.
I use the live view histogram as a guide when setting the shutter speed.
I aim to achieve as even a distribution of tones as possible. This helps me to produce the best results when it comes to post processing.
If you would like to understand how to read a histogram check out the video below.
The histogram is extremely important when it comes to avoiding blown out the highlights.
This is where the highlights are recorded as pure white. It is also known as ‘clipping the highlights’.
In this case there is essentially no tonal information at all in the areas that have been clipped. The result is that it won’t be possible to recover any detail from these areas, regardless of the software that you use for post-processing.
In most cases I do everything that I can to ensure that I do not clip the highlights.
Exposure simulation is a feature where live view aims to simulate exactly how a photograph will look once the shot is taken.
I use this along with the histogram to set the shutter speed. As I change the shutter speed the image shown on the LCD will get lighter or darker accordingly.
This gives me instant feedback allowing me to determine if the shot will be over or under exposed so that I can adjust the shutter speed as necessary.
Expose to the Right
I generally use the histogram to ensure I have an even distribution of tones. However, there is another approach know as ‘expose to the right’.
In this case the aim is to set the exposure so that the image is as bright as possible without clipping the highlights. It gets its name because the brighter tones are displayed on the right hand side of the histogram.
The theory is that by doing so you will capture the maximum amount of information about a scene. Try it for yourself:
- Take a shot with the exposure set as bright as possible without clipping the highlights
- Then increase the shutter speed by 2 stops and take a second shot (this image should be darker than the first)
- Finally compare the file sizes of the 2 images. The first will be larger because it contains more information
This is a perfectly valid approach and many photographers use it to great effect. However, it is still my preference to get as balanced an exposure as possible.
There are some other advantages to shooting in manual mode.
When shooting panoramas it is important that each shot is exposed in the same way. You don’t want the camera changing the exposure half way through.
It is also useful to be comfortable taking control of shutter speed when attempting long exposures. Most cameras require exposures over 30 seconds to be captured using ‘bulb’ mode, requiring the photographer to time the exposure them self.
A camera’s dynamic range describes the range of tones that it is capable of capturing.
Expressed in ‘stops’ it is essentially the difference between the darkest and the lightest tones that it can capture. For example my Canon EOS 6D has a dynamic range of approximately 12 stops.
In comparison the dynamic range of the Nikon D850 is closer to 15 stops. This means that the Nikon can capture a greater range of tones than my Canon.
If the dynamic range of a scene is within that of the camera it is relatively simple to correctly expose the image.
However, if the dynamic range of a scene exceeds that of the camera the image will suffer from either clipped highlights, clipped shadows or both!
One of the ways to cope with scenes with a higher dynamic range than that of your camera is HDR blending.
This involves taking 3 or more shots at different exposures and blending them together using software such as Adobe Lightroom. The process uses different parts from each exposure to produce an image with detail in both the shadows and the highlights.
Sounds perfect? Well, it isn’t without its problems.
The biggest problem with HDR blending is stitching the three images together. If there is any movement at all in the scene the chances are you will get a weird ghosting effect.
I also find that HDR images are more prone to fringing, particularly around the edges of dark branches that are silhouetted against a bright sky.
But for me the biggest problem is tonality. I often find that the tones in my HDR images lack a degree of subtlety making them seem unnatural. In fact at the time of writing there is only 1 HDR image in my portfolio.
One alternative to HDR is a process know as luminosity masking which is growing in popularity.
To date I have not tried blending images using luminosity masks so I shall reserve judgement until I have.
Until I have had experimented with luminosity masks I will continue to deal with scenes with a high dynamic range as I always have done. By using a graduated ND filter to darken the sky (typically the brightest part of a landscape photograph).
Failing that I will avoid shooting them entirely.
Typically I will only shoot in the direction of the sun until is has peaked above the hills. I then go and look for compositions where the sun is off to the side. In such cases the dynamic range of the scene is generally within that of the camera.
Modern cameras are extremely sophisticated but they are easily fooled. In certain conditions they can be tricked into under or over exposing your images.
Shooting in manual mode allows you to take control of both aperture and shutter speed helping you to get the perfect exposure ever time.
For more on using manual exposure mode check out the video below.