How to use camera exposure

Photography Gear

When browsing through photographic works, you might come across pictures in which certain sections are overly illuminated, resulting in lost image details. Conversely, certain parts of the frame might be excessively shadowed, obscuring all the intricate aspects of the image. A seasoned photographer would promptly point out that in both scenarios, the exposure settings are inaccurate.

What is exposure

What does exposure mean in photography? Exposure is a fundamental concept in photography. When you first start learning about photography, whether it’s from textbooks, online tutorials, or video courses, you’ll quickly come across the concept of exposure and its importance in capturing great photos. These resources will then go on to explain in detail how to manipulate exposure settings on your camera and how to choose the right exposure for different situations.

Exposure refers to the amount of light that reaches the photosensitive image sensor in a digital camera. In order to capture a photograph, the light that is reflected off the objects in the scene must pass through the camera lens and reach the image sensor. The exposure determines how much light reaches the sensor over a certain period of time.

The overall brightness of the resulting image depends on the exposure. If there is not enough light, the image will appear dark, while an excess of light will result in a brighter image.

To achieve a flawlessly vivid photo, it is crucial to accurately adjust the exposure, which means having the ability to alter it in any manner. In order to accomplish this, one can manipulate the amount of light that reaches the image sensor and also adjust the sensor’s sensitivity.

Technically speaking, a camera achieves this by modifying the aperture, shutter speed, and ISO sensitivity.

Aperture

An aperture is a dark barrier inside a camera lens that has a varying diameter opening. When the aperture size expands, more light enters the camera sensor, resulting in a brighter image. Conversely, when the aperture diameter shrinks, the light flux decreases, causing the image to lose its brightness.

The ratio of the focal length of the lens (f) to the diameter of the aperture opening determines the aperture value (aperture number). The series of aperture numbers include f/1, f/1.4, f/2, and so on. Alternatively, they can be written as 2.8, 4, 5.6, 8, 11, 16, 16, 22, 32, 45, and 64. The specific method of notation is not significant, but it is important to note that each subsequent aperture value corresponds to half the illuminance of the previous one.

Shutter speed

The shutter speed refers to the amount of time that the camera’s specially designed shutter remains open, enabling light to pass through and reach the image sensor. In photography, shutter speed is typically measured in seconds or fractions of seconds, such as 30, 15, 8, 4, 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, and so on. These values are the standard increments on the shutter speed scale, which is widely used in virtually all camera models.

Light Sensitivity

ISO, or light sensitivity, is a crucial factor in determining how well a camera sensor responds to light. It is measured in units that increase exponentially, such as 100, 200, 400, and so on, with each value being twice as high as the previous one. When you raise the ISO, you make the sensor more sensitive to light, resulting in a brighter frame. However, this also increases the level of digital noise, which can impact the overall image quality.

Exposure levels in photography are determined by exposure values (EV), which are a combination of aperture, shutter speed, and ISO sensitivity required to capture a properly exposed image under specific lighting conditions. Exposure values are closely related to Light Values (LV), which represent the level of illumination in a scene. In fact, it is commonly accepted that at ISO 100, EV is equal to LV.

For convenience, tables have been created to determine LV for various typical photographic scenarios, as well as EV values corresponding to different aperture and shutter speed combinations. These tables simplify the process of calculating exposures.

Relationship of parameters

To modify the amount of light that reaches the camera sensor, you have the option to adjust the aperture and shutter speed. These two settings, known as the exposure ratio, play a crucial role in determining the level of exposure. It’s important to note that achieving the same EV in a photograph can be accomplished with different aperture and shutter speed combinations, as they are interconnected.

For instance, if you were to select an aperture of 2.0 and a shutter speed of 1/30, the resulting EV value would be 7. Similarly, using an aperture of 4.0 and a shutter speed of 1/8 would also result in an EV of 7. The relationship between aperture and shutter speed allows for various combinations to achieve the desired exposure level.

This principle can be attributed to the Bunsen-Roscoe law, also known as the law of interchangeability. This law highlights the practical significance of aperture and shutter speed, as they serve not only to expose the frame, but also to determine the level of light in the image.

Aperture is also accountable for controlling depth of field, while the accurate shutter speed is essential for capturing moving subjects without any undesired blurriness. The principle of interdependence permits us to achieve the proper exposure by carefully choosing the exposure settings that guarantee a sharp and crisp image.

In the example mentioned above, the frame was exposed at ISO 100. In the 20th century, specifically during the film camera era, adjusting light sensitivity was not commonly utilized for photoexposure. In order to do so, one would have needed to switch the film for each frame to a different film with the desired ISO value, which was impractical.

However, with the introduction of digital cameras, it became feasible to expose an image by altering the light sensitivity of the sensor. While professional photographers still recommend setting the ISO value to its minimum and changing it as infrequently as possible, modern cameras enable users to capture high-quality photos at higher ISO values (up to 1600). In this case as well, the exposure table for different aperture and shutter speeds remains applicable.

Just keep in mind that when you double the ISO value, the corresponding exposure number increases by 1 unit.

Using a histogram in exposure evaluation

One of the benefits of using a digital camera is the instant ability to evaluate the quality of the captured image through the LCD screen. When using the Live view mode, the screen presents a real-time view of the subjects being focused on by the camera. This provides the opportunity to properly frame the shot, fine-tune sharpness, and establish focus.

However, it’s worth noting that the image quality and backlighting of the screen can distort the balance of light and shadow, thus making it difficult to accurately expose the image.

Nonetheless, modern cameras are equipped with a feature that effectively addresses this issue. It comes in the form of a histogram, which visually represents the distribution of brightness levels within an image. This enables the photographer to promptly assess the exposure level and make necessary adjustments to the camera’s settings.

Once the picture is captured, the screen can show the histogram. Some camera models even include a histogram during the setup stage before shooting. Regrettably, numerous amateur photographers fail to make the most of the histogram’s features, despite understanding what it is, as they consider it too complicated and obscure.

The histogram’s x-axis displays the brightness values of the image, ranging from black (shown as the leftmost point) to white (represented by the rightmost point). On the y-axis, the number of pixels with corresponding brightness levels is depicted. This graph visually represents the brightness of the resulting image and potential exposure errors.

In order to accurately interpret the histogram, mentally divide its x-axis into three equal sections. If the majority of pixels are found within the left section and are touching the left border, it indicates that the image is likely underexposed.

If the pixels are clustered towards the right border of the histogram, the image is most likely overexposed.

If the majority of pixels are found in the central region of the histogram, then the exposure is deemed to be correct.

By utilizing this function, you can easily determine the precision of your exposure, which is incredibly useful, particularly in instances where you are shooting in automatic mode. There are occasions when the camera’s microprocessor may make errors in certain scenes, and if the exposure is not promptly adjusted, it can severely harm your photographs. However, if you are knowledgeable about how to interpret the histogram, you can prevent these issues from occurring.

Exposure scale and bracketing technique in photography

In order to unlock the complete potential of your digital camera, it is crucial to grasp the principles of exposure scale and bracketing.

An exposure meter, which is a built-in device in a digital camera, is responsible for measuring the light reflected from the subject, instead of directly measuring the exposure itself.

The camera’s microprocessor controls the exposure of the frame based on its algorithms. The camera screen and viewfinder display a scale with negative and positive numbers (typically ranging from -3 to 3), which represent the exposure meter readings. These numbers indicate the level of exposure. When using automatic modes, the arrow on the scale points to zero, indicating that the camera’s processor is automatically adjusting the exposure. In manual mode, if the arrow shifts to the right, it suggests that the photo will be backlit. Conversely, if the arrow is in the negative range, the frame will be darker.

When using automatic modes, the exposure meter arrow will always indicate 0, suggesting that the exposure is accurate. However, this is not always the case. The exposure meter is calibrated based on the subject’s 18% reflectivity, assuming daytime lighting with some cloudiness. If the shooting conditions deviate significantly from these standard conditions, the camera’s automatic settings may frequently result in incorrect exposure.

To address this issue, manual exposure correction can be easily achieved using the scale. For instance, in Canon cameras, you can switch to one of the creative modes, press the +/- button, and then adjust the frame’s brightness by rotating the control dial and moving the indicator arrow to the right or left. The camera will automatically set the aperture, shutter speed, and ISO accordingly.

What is exposure bracketing? It’s a technique used to capture better photos under challenging conditions like low light and time constraints. The process involves taking a series of photos (typically 3 to 5) at different exposure levels. Usually, the first photo is captured at 0 on the exposure meter scale. Then, the EV value is increased by 1 step and another photo is taken. Finally, the third picture is taken after decreasing the EV by 1 step. The best photo is selected afterwards. The size of the step can be adjusted – the system allows for gradation from 1/3 EV to a full EV.

Professional cameras come with the ability to manually adjust bracketing. This feature lets you choose different settings to create artistic photos. It is often used to create HDR images, where multiple photos taken at different ISO levels are combined into one through post-processing.

Mid-range cameras have the AEB (Auto Exposure Bracketing) mode, which automatically takes multiple shots with different exposure levels after pressing the shutter button once.

Exposure metering mechanism

• The exposure meter in manual control measures the light in the scene and provides a reading to the photographer, who can then adjust the camera settings accordingly.
• The exposure meter in autoexposure mode uses the camera’s microprocessor to analyze the scene and determine the optimal exposure settings.

Understanding exposure metering is crucial for achieving desired results in photography. It allows photographers to control the brightness and exposure of their images, ensuring optimal quality and artistic expression.

Hint! The selection of the metering mode is determined by the shooting conditions. If the lighting in the frame is relatively consistent and the objects have similar tones of brightness, it is advisable to opt for matrix metering.