In the Part I, we learnt about the basics of Exposure. In this part, let us examine how we can find the optimum exposure for various scenarios that we encounter on day to day basis.
How to Achieve Optimum Exposure for a High-key Scene
A high-key scene contains lower dynamic range than a good consumer/pro camera can handle. There will be a uniform distribution of light in the high-key scene.
Foggy, rainy and cloudy days usually lead to high-key scene since most of the scene will be equally lit.
High-key scene usually contains the uniform lighting, yielding to lower Dynamic Range
Consider our 5-stop dynamic range camera for example. Assume that we are photographing a waterfall on a cloudy day. It is a well distributed light and mostly the scene is having two dominant colors, white and green.
If you meter the waterfalls, then the metering may indicate an f/11 as in our example study. So, we have a dynamic range of f/5.6 to f/22.
But as you know, waterfall is the brightest element in the entire scene. There is no subject/object at f/16 and f/22. However, we would have lot of details in the green area or the surroundings. If the shadow regions need a smaller aperture than f/5.6, you will have those region turn to black.
If you happen to expose the scene with f/11 aperture, then you would end up with a darker or an underexposed image.
This is the time, when you have to make a decision as a photographer to utilize the opportunity to come up with an optimum exposure.
If you decide to expose the waterfalls at f/5.6 by using exposure compensation of +2, then you will get a 4-stop dynamic range (f/2.8 to f/8) to represent the shadow region or the surrounding. This technique is also called as ETTR (Expose To The Right).
In this process, we are opening up the aperture by 2 stops and allowing more light to pass through the lens.
This way you will have a virtually greater dynamic range to represent the entire region in a much more pleasing way leading to an optimum exposure.
How to Achieve Optimum Exposure for a Low-key Scene
A low-key scene is exactly opposite to a high-key scene. It has a very high dynamic range than a consumer/pro camera can handle. Mid-day sun yields a low-key scene with lot of highlights and dark shadows creating a very high dynamic range that most of the cameras may not be able to handle.
Low-key scene usually contains the harsh lighting creating deeper shadows yielding to a higher Dynamic Range
Note that low-key scene is not same as HDR (High Dynamic Range) scene. Usually the HDR scene will usually have various luminance levels anywhere from pure black to mid-tones to pure white.
The low-key scene will have shades of blacks and whites at either extremes but rarely have the mid-tones.
Consider our 5-stop dynamic range camera for example. Assume that we are photographing the same waterfall on a sunny day at noon. The light is harsh and casting the shadows at various regions in the surrounding.
If you meter the waterfalls, then the metering may indicate an f/32 and for the surrounding shadow region could require as high an aperture as f/4. It requires at least 7-stop dynamic range to represent both the waterfalls and surrounding regions with details.
Note that, though the scene has higher dynamic range, there is not much to represent in the mid-tones. We have our main subject, waterfalls, at f/32 and the surrounding may be between f/4 to f/8 but nothing in-between f/8 to f/22.
In such cases, we could consider exposing separately for highlights (waterfalls) and shadow regions (surroundings) so that we can later blend these two exposures in Post-Processing software like Adobe Photoshop.
Note that, sometimes overexposing or underexposing a scene is desirable.
Sunset and Sunrise times naturally lead to low-key scenes since Sun is always tens of hundreds of time brighter than anything else in the scene.
In case of photographing Sunset or Sunrise, we may have to overexpose the sun to show how powerful the sunlight is.
Whereas, in case of before sunrise or after sunset, we may want to underexpose the surrounding objects to get the silhouette effect to emphasize more on bright and vibrant colors in the sky.
How to Achieve Optimum Exposure for Normal Scenes
Generally, most scenes have the dynamic range that can be covered using the exposure range of the camera.
As described in the Camera Metering Modes article, the camera metering sensor(s) are calibrated to calculate the proper exposure for normal subjects of an average brightness. In most of the normal scenes, the metering sensor should be able to give an indication of the optimum exposure.
However, at times, we may opt to slightly underexpose or overexpose a photograph to achieve desired results.
It is almost always good to Expose To The Right (ETTR) of the histogram to retain the greater details in the shadow regions.
In some cases, when the scene contains a mid-toned main subject and a bright background like sky, we might have to underexpose a bit to avoid blowing out the background.
How to Achieve Optimum Exposure for HDR Scenes
Some scenes will have High Dynamic Range (HDR) than what a camera can handle. This is usually true in case of vast landscapes with various objects that have different luminous intensities and color.
Each exposure should be made by following the same principle that we follow in case of normal scenes.
In the next article, we discuss about effects of filters on Exposure.
Do you have anything to add? Do you shoot different kind of scenes like low key, high key and HDR? Would you like to bring out any other scenario?
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