The Essential Guide To Landscape Photography P2 – Camera Exposure

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Posted by deadgrateful on Monday, September 6, 2010 · Leave a Comment 

Christopher Burkett - Fir, Snow & Mountainside, Wyoming 1989

Exposure is one of the most important aspects of photography and yet to many it is a complex art that is often overlooked. Image exposure is based on science yet is still open to artistic interpretation. Whilst one photographer may think an image has an accurate exposure, in that it captures the mood or essence of a scene, another may decide it inaccurate if it fails to conform to technical rules. This is especially true when considering landscape photography, as the difference in exposure can dramatically affect the outcome of the image. For example, the below image of a waterfall looks completely different when the exposure is altered slightly.

ISO 100 | F22 | 1/2 Sec

ISO 1600 | F4 | 1000/sec

Camera Settings and Terminology

There are several terms it is important to understand when learning about exposure. The main three are: shutter speed, aperture and ISO. To get creative with landscape photography, it is also essential to use a camera which has manual controls over these functions. Put in simple terms  the aperture is the amount of light reaching the sensitised material, the ISO is the sensitivity of the material and the shutter speed is the length of time the sensitised material is exposed to the light.

Too little light and/or too short a time will result in underexposure, yet too much light and/or too long a time will result in overexposure. It is important to get just the right amount of light for the correct length of time given the sensitivity of the material, to record the scene as you see it in your mind’s eye.

ISO Rating

The ISO (standing for International Standards Organisation) rating is the measure of a film’s sensitivity to light. A film with a low ISO rating, such as Fuji Velvia 50 is less sensitive to light than a film with a higher ISO. This means that a low ISO film needs more light than a film with a higher ISO rating would need. ISO follows a geometric progression. Each time the ISO number doubles, the amount of light required is halved. In digital cameras the ISO refers to the sensitivity of the cameras digital sensor rather than the film. A great benefit of a digital SLR over its film counterpart is that the ISO rating can be altered shot by shot. Doing this on a film camera will not change the sensitivity of the film, but will “push” or “pull” it instead.

Aperture

The aperture of a lens is a mechanical hole that alters the amount of light that reaches the sensor or film inside the camera. Changing the size of the aperture allows you to decide how much light reaches the film at any given point. Aperture is measured using f-stops and the quality of your lens will dictate the range of f-stops offered (generally speaking, the wider the maximum aperture, the better the quality of the lens).

Controlling exposure via aperture will affect the depth of field (the proportion of the image that is in focus). The wider the aperture the less depth of field you have and vice versa. This is an important factor to take into consideration when deciding on your exposure. For example, an image with detail in both the foreground and background will require a narrower aperture (larger f-stop number) which in turn will necessitate a slower shutter speed or greater ISO. In the example below you can see the effect of increasing the aperture.

Shutter speed

The shutter speed is the length of time that the light falls on the sensor or film. It is measured in minutes, seconds and fractions of seconds. All modern SLR cameras have a comprehensive selection of preset shutter speeds. They will also have an option to time the shutter release manually (this is usually marked as B [bulb] or T [time]). Similarly to the Aperture and ISO, changing the shutter speed by a single stop will either half or double the exposure. E.g. changing the shutter speed from 1/2 of a second to 1/4 of a second will half the length of time that the shutter is open for, equating to a one-stop reduction in exposure.

Depending on your subject you may want to use either a slow or fast shutter speed. E.g. the image below would have been blurry and unrecognisable had it not been for the relatively fast shutter speed of 1/500sec.

Combining the three

Achieving perfect exposure requires a decent understanding of the three controls outlined above and any change in one variable must be compensated by a change in another. Certain situations will dictate some of the settings e.g. photographing moving wildlife in lowlight without a tripod will necessitate an extremely high ISO setting so as to avoid the blurring of the subject. This characteristic of exposure is known as reciprocity and it states that any change in one variable is compensated for by an equal and opposite change in another.

Reciprocity law failure

When dealing with long exposures of over one second the law of reciprocity has a tendency to fail. This is because film, and to some degree sensors, become less sensitive to light the longer they are exposed. Therefore, when shooting with shutter speeds over one seconds it is important to allow more light to hit the film or sensor. The table below gives guidelines for different films:

Digital versus film exposure

Whilst digital photography is now the norm there are certain issues that affect digital SLR cameras more than their film counterparts. Digital cameras often feature a very wide latitude, offering incredible detail in the shadows of an image. This does however mean that the highlights can sometimes ‘burn-out’ in brightly lit conditions. It is therefore advisable to very slightly under expose by half a stop from the suggested reading.

Different modes

Every SLR camera will feature at least four modes for controlling the exposure. These are:

Automatic – in this mode the camera will try to make a judgement based on the type of metering selected. When using this mode, an experienced photographer may prefer to use the matrix metering system as it will give an exposure reading based on many different areas in the composition.

Aperture priority – here the camera will automatically adjust the shutter speed (and ISO if set on auto) to compensate for the manual change in aperture. This mode is best used when the photographer wishes to control the images depth of field that is not concerned with the length of the exposure.

Shutter priority – this mode will automatically adjust the aperture (and ISO if set on auto) to compensate for the manual change in shutter speed. This mode is best used when the photographer wishes to control the length of the exposure e.g. when taking pictures of moving water or grass blowing in the wind.

Manual mode – when the camera is set to manual none of the settings will automatically compensate the changes to the others. This mode is best used when using creative filters, working with a tripod, longer exposures and night-time photography. In certain cases the automatic settings on the camera will not be able to accurately reproduce the lighting of the subject. If this happens it is advisable to use the automatic suggested settings as a starting point and then to adjust exposure manually.

Contrast

Contrast is the measure of the difference between the highlights and shadows in a given scene. Unfortunately the human eye is capable of seeing much more detail in these areas than film or digital sensors. It is therefore important to learn the individual characteristics of the medium you’re using to record the image. In order to reduce the contrast the lights must be diffused somehow (this could be in the form of could cover or heavy foliage).

Images taken under a harsh light source unknown as having a ‘hard’ quality and images shot under diffused light sources are known as ‘soft’. It is a matter of taste as to which lighting source suits any given subject. Landscape photographers (especially those used to shooting with Fuji Velvia colour film) will often prefer to shoot under harsh conditions. E.g. sunlight breaking through dark storm clouds and illuminating the landscape. On the other hand, seasoned black-and-white photographers enjoy the wide dynamic range offered when shooting under a lightly overcast sky.

It is important to remember that shadows give an image a sense of depth, it is therefore a case of balancing the amount of shadows (dark) and highlights (light) in the image while still maintaining a high level of detail. Unfortunately cheaper DSLR cameras often cram a high number of megapixels into relatively small sensor causing a reduced dynamic range. One way around this is to combine several exposures in a software package such as Adobe Photoshop.

Follow The Sun

When working outdoors and shooting landscapes the single most important element to consider is the lighting position. To try to simulate the three-dimensional quality of a landscape on film is no easy task.

Front lighting
In the past it was always considered bad practice to light from the front and photography students had the mantra “Always photograph with the sun behind you” drilled into them. This was mainly due to limitations of cameras rather than it had to do with good photography. Frontal lighting will reduce the overall contrast and flatten out details and texture which can be advantageous when trying to record a subject’s key features.

Side lighting
light that falls on the subject from the side will create shadows that enhance texture and define the sides of multi dimensional objects such as trees and buildings. It is the shadows that give form to your photographs and help to turn them from flat pieces of paper into pictures with high visual energy.

Lighting from above
When the sun is overhead (typically in the middle of the day) the lighting will have a harsh quality which is often avoided by photographers. However if your subject has a horizontally formed texture lighting it from above will enhance the shadows and emphasise form.

Backlighting
Often overlooked backlighting can produce artistic results when combined with correct exposures. Backlighting is often the easiest way to produce a silhouette or halo effect.

Metering the light

When we look at an object what we actually see is reflected light. This can be measured with the reflected light meter otherwise known as a luminance meter. The brightness of an object is decided by the amount of light it reflects back and a light meter will provide a visual representation of this, either in the form of an exposure value (EV) or as an actual aperture/shutter speed combination. As the reflected light meter measures the light coming back from a subject it can be used from a distance. This means that it can be built into the body of the camera, also known as TTL metering.

Reflected light meters are calibrated to read everything as 18% grey (middle tone) however different subjects reflect different amounts of light. In practice this means that the light meter will assume that the subject is reflecting 18% of the light falling on it and will give a reading based on that. Any subject that is lighter or darker than 18% grey, for example white or black, will be rendered incorrectly. This can mean that it is very difficult to accurately reproduce pure white or black objects using TTL metering.

A simple trick to combat this is to increase the exposure value by two stops when shooting something white, and to decrease by two stops when shooting something black.

Incident light meters measure the light falling on the subject rather than the light reflected from it. It is easy to distinguish an incident light meter as it will have a white plastic dome or cone attached to it, which averages the total amount of light falling on it before the diffused level of light is measured by the meters cell. Incident light meters work best when placed very close to the subject. Because of this they are less vulnerable to high contrast lighting conditions.

Modern Sekonic light meters often feature both incident and reflective modes

Types of metering

Matrix metering
Matrix metering is a multi segment metering system that takes readings from different areas of the scene and calculates an exposure based on a combination of factors. Different camera manufacturers use different matrix metering systems, each giving different qualities of results. When photographing a scene where the level of contrast or dynamic range is within that of the latitude of sensor matrix metering will usually yield accurate results. It is often the only option when using compact digital cameras.

Centre weighted metering
When put in centre weighted metering mode a TTL meter reads the light across the whole scene but weighs around 75% of the reading towards a large centre circle. This is perfect when shooting portraiture as the subject stands out from the background yet still fills a large proportion of the image space.

Spot metering
Spot metering a subject takes a reading from a very small part of the subject, giving incredibly accurate results. It is also useful for calculating the EV difference between any given area is in a scene. When shooting landscapes a spot meter is often all that is needed to obtain pleasing results.

Bracketing

In some situations are it pays to have multiple exposures of the same image is. Bracketing is most useful when shooting film as you will be unable to compensate for your mistakes once the film is developed. The bracketing function on an SLR will provide a variance option for your exposure. Typically, the variance should be around a 1/3-1/2 stop but you may wish to go as far as +/-1 stop.

Related posts:

1. Essential Guide To Landscape Photography – P1: Camera Equipment
2. Top tips for studio photography – Shooting tethered
3. Top tips for studio photography – Using snoots, grids and barndoors
4. 1 – 3 Head Lighting Positions
5. HDR Photography Tutorial – 10 Crucial Do’s and Dont’s