By Eugene Struthers
Definition: Dynamic range is a measure of the camera’s ability to record useful detail in the brightest and darkest parts of a scene. It is measured in EV (Exposure values), the higher the EV amount the better. It is the ability to pull back digital information “finer hidden detail” from within our images in the shadows and highlights.
The term dynamic range is closely associated with HDR “High Dynamic Range”. But most people don’t really know what it is and why it has to be high. Put simply, dynamic range describes the largest and smallest possible values for light intensity measurement. Dynamic range is the difference between the darkest area in the image and the brightest area of the image, that the camera is able to record “unusable information” and still have colour, texture and detail in the shadows and highlights areas of that image. It is interpreted as the measurement between the whitest whites and the blackest blacks in an image. And this allows us to determine the highest and lowest values of contrast density & luminance that our camera can and has the ability to capture.
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The human eye can only see about 24 stops of light when we take into account the variations in different light levels. (Understanding colour). A film camera can capture 12 stops of light. And this is the main reason why a lot of professional photographers choose real expensive cameras like the Nikon D810, Fujifilm X-E1, Sony A7r, Canon 1 Dx, Samsung NX1, Canon 5D mK3, Olympus OM-D E-M1, Pansonic GH4. It means that they can see almost as much (in terms of stops) as our eyes can.
Most digital camera’s capture only about 5-8 stops of light. And there is a noticeable big difference between what we can see and what our camera can capture. Dynamic range is expressed in stops, whereby each stop is a doubling of the light level or a halving of light. The number of stops of light that a camera is able to cover without clipping, the greater its dynamic range and thus the better the camera. Click here to understand stops of light: (Stops of light). The more stops of light that a camera’s sensor can see and capture, the higher the dynamic range.
In the image above, we can see that there is a smooth transition from white to black and we are able to verify that there is an innumerable amount of grey tones between the blackest and whitest values in this gradient.
Now if we take into consideration that our digital camera can only capture 5-8 stops of light. The dynamic range gradient becomes more limited.
Our camera will only have the ability to capture a small proportion of white, grey and
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black sections. The camera sensor will make a quick judgement as to what to expose correctly for based on its limited dynamic range available. By either overexposing “clipping” the background or underexposing the foreground.
An example would be if we were photographing a nude model outdoors on a sunny day. You expose for the background to capture the details of the clouds and blue sky but your model falls into a deep shadow and almost becomes a silhouette. To solve this issue you would need to introduce a speedlites /flash. (More on this in the Speedlite/Flash tutorial). Or have a camera with a greater dynamic range.
Our aim as photographers is to have a greater tonal range (density in contrast & luminance) with a wider dynamic range. This will allow our camera to capture all the detail in the shadows and highlights. Dynamic range will vary from camera to camera but the ratio will be similar. Whether you use a digital sensor, roll of film, digital file or a printer. It cannot perceive the same dynamic range to that of a human eye. Each medium has its own dynamic range, and our main purpose as photographers is to try and extend the range of tones in between the maximum and minimum tonal values to create a more true representation of what our eyes see and what we want to actually capture via our camera.
In the metering tutorial “Exposure values” Click here: How to use a light meter. We looked into how to use Exposure values to achieve a higher degree of accuracy and to know precisely how to meter for a scene of great contrast and luminance. Scenes where there is a mix of both extreme brightness and shadows. That will throw our camera off, and prevent it from capturing the detail in both of these areas. The photographer will have to compromise and decide whether to expose for the shadows or the highlights. The ability to capture an image with a wide range of tones with a greater range of tonal values between the black and white values is the main aim when comparing dynamic range of different cameras, films, paper, printer etc.
Click here to learn more: The Zone system
To achieve an accurate indication of the measurement of a specific dynamic range in camera. We would use a light meter / Exposure value chart (Exposure compensation) or calculate the individual stop values for Aperture, Shutter speed and ISO and apply these individually to light conditions at a given time at a particular scene. Without getting too technical at this stage (as I cover this topic again in more detail in the advanced photography course). It is assumed that cameras with larger photosites or a greater pixel size will have the ability to record a greater dynamic range. As a point of reference, larger sensors and lower resolutions are an indication of a larger photosite, as larger sensors will have more room to accommodate larger photosites. And it is common knowledge that sensors with a lower resolution will allow for the photosites to be larger than those with a higher resolution. Photosites that are larger collect more light and subsequently record more light detail and a higher contrast ratio levels.
To fully understand dynamic range, this tutorial should be read in conjunction with the tutorials (How to use a light meter, Histogram , Light temperature, Understanding colour).
In the Click here: Digital photography course, we go into more detail about photons, photosites, megapixels, sensors, resolution, CMOS (Complementary Metal Oxide Semiconductors), CCD (Charged-Coupled Device).
Next months tutorial will be “High Dynamic range” and how to create the HDR effect using editing software.
