User:Khavs/OLES2129/draft/The Exposure Triangle

The Exposure Triangle Depicting all the Variables. Figs. 1 (Credit: WClark/Samsara)

Not to be confused with Exposure (photography).

The Exposure triangle is a visual and theoretical understanding of the three main variables required to obtain an exposure. Shutter speed, Aperture and ISO each individually effect the final exposure. The correct balance of these variables produces a properly exposed image. It is very important that a photographer has a strong understanding of the exposure triangle as it is the base fundamental principal of the creation of every image. Understanding the exposure triangle allows the photographer to create a correctly exposed image

The exposure triangle is made up of three elements shutter speed, aperture and ISO. Aperture is the opening in the lens which controls the amount of light that comes through the lens. Aperture also controls the depth of field. Shutter speed controls the duration the sensor of the camera is open to light. ISO is the sensitivity of the camera’s sensor to light. The balance of these three variables allow the photographer to obtain the exposure they want.

Three Elements

Shutter Speed

Image depicting the same subject with different in shutter speed. Figs. 2.1 (Credit: User:Nevit)

Image showing the effects of a longer shutter speed on a waterfall.

Shutter Speed also called exposure time controls the duration the sensor is open to light. It works by moving a curtain in front of the sensor. There are many types of shutter including the roller blind. A roller blind shutter consists of two main moving parts a bottom door and a top door. The shutter fires when the trigger is pressed. Once pressed one of the doors moves from top to bottom exposing the sensor to light for a pre desired amount of time. Once the pre-set time is over another door falls from top to bottom covering the sensor. The shutter is powered by a spring where the tension is increased as the shutter speed is increased. The first commercially produced camera with this shutter is the Loman Reflex in 1889.

Shutter Speed is measured is values of time. The value can range from many seconds to small divisions of a second. Shutter speed controls many factors including sharpness. A faster shutter speed (smaller division of a second) will result in a freezing time. Which will produce a sharp image. While a longer shutter speed (many seconds) will result in a blurry image. The values are usually measured in fractions of seconds or seconds. Camera have the possibility of increasing the time to many seconds or may even have a “Bulb”. The Bulb mode allows the user of the camera to hold down the shutter for as long of a time they desire. Being a longer exposure, the final image is prone to have camera shake, so a tripod is necessary. A difference in shutter speed results in a different look in the image. A shorter shutter speed is used for freezing time for fast action scenes. A longer shutter speed can result in motion to be added to the final scene like for a long exposure of a waterfall.

Aperture

Aperture how open of closed the lens iris is or the size of the hole in the lens that lets light onto the sensor of the camera. It functions by using a mechanical diaphragm which can be opened and closed which provides a bigger or smaller opening in the lens. It opens and closes a hole allowing more or less light into the sensor. Like the human eye the lens has a diaphragm it opens and closes depending on how much light is needed. Aperture allows you to control the amount of light that comes through the lens. Aperture is measured with a F Value which represents how big or small the opening is. F Values are written as f/1.8 or f/22. The f number is a representation of the focal range in a fraction. A 500mm lens with a F/4 has an opening of 125mm. F values are written backwards a smaller opening means a bigger number like “f/22” while a wider opening means a smaller number like “f/1.8”. Aperture also effects depth of field. Depth of field is defined as the area of an image that is in focus. The term “shallow depth of field” means that only a small part of the image is in focus. While a “deep depth of field” means more of the image is in focus. Each are used in their own mediums. A shallow depth of field results in a blurring effect in the background which provide a special look. df

Image showing the effect on depth of field with a smaller f number. Figs. 2.2 (Credit: )

ISO

Image showing the comparsion of images taken with diffrent ISO. Top portion is at ISO 100 and the bottom is at ISO 1600. Figs. 2.3 (Credit: User:HuttyMcphoo)

ISO is the sensitivity of the camera’s sensor to light. It is based on film speed. 35mm film has a set ISO which was how sensitive the roll is to light. The smaller number (ISO100) is not as sensitive to light meaning it was only used on a bright sunny day. It is the same in digital cameras the smaller ISO number means the sensor is less sensitive to light. While a larger ISO (ISO 3200) means the sensor is more sensitive to light. As you increase the ISO it allows for photos in low light with acceptable shutter speed to avoid shutter shake. ISO may have some adverse effects such as; lower quality and random background noise. Background noise also called grain produces unpleasant effect in the image. A bigger ISO mean more noise but allows for a higher shutter speed in lower light.

Exposure Value

The understanding of quality of light. The EV is a calculation made up of the aperture value and exposure time. It is used to calculate to show exposure time and aperture that produce the same level of exposure. The calculation is $\log _{2}(n^{2}/t)$. Where $n$is apeture and $t$is exposure time. This formula produces a EV value on a scale of -6 to 23. The range most cameras will calculate is -6 to 15. -6 is “Night, away from city lights, subject under starlight only.” While 15 is “subjects in bright or hazy sun (Sunny f/16 rule).”

F stop

The base of how Shutter speed, aperture and ISO is measured in correlation to itself and each other. The difference between setting a value and increasing it is measured in stops of light or f stop. A stop is doubling or halving the light that makes up an exposure.

Methodology

Traditional

For any photograph there is only one mathematically correct exposure but there will be many combinations of shutter speed, aperture and ISO to create that exposure. The exposure triangle is a combination of three variables which allow for the photograph to obtain the exposure they desire. A photographer must balance all three values to allow for a correctly exposed image. The combination of shutter speed, aperture provides a properly exposed image. The process in using the exposure triangle starts with the photographer deciding on what image they would like to create. Once the photographer has decided on what image they would like. Once an image has been decided on the photographer will then pick either a exposure time or aperture value to create the image that the photographer wants based on what image they would like to create. Once that value is decided on a balance between the remaining two variables is made allowing for a perfectly exposed image. During this process the photographer thinks about the ambient light around them. And how that will affect the settings they have decided on.

The bucket analogy

An understanding if a change of one of the three variable of shutter speed, aperture and ISO one or both other to values need to be adjusted in the opposite direction. Using the bucket analogy, we can gain a deeper understanding of the exposure triangle.

The bucket analogy compare light to rain and filling up buckets with fain instead of light hitting a sensor to make an image. Shutter speed is the length of time the bucket is left out, how hard it is raining is aperture and ISO is how wide the opening of the bucket is. In the bucket analogy it maintains one value as the same and as we change other values around it what would happen to the final outcome. It’s an understanding that many different settings can be used to achieve the same goal. If we have the same heavy rain (aperture) and we kept the buckets out in the rain for the same time (Shutter speed) but had different size openings (ISO) it would result in different amounts of water collected as a larger opening (higher ISO) would fill up its bucket more then one with a smaller opening. To obtain the same exposure we would need to change another value we could increase the time out in the rain to longer to allow for the bucket with a smaller opening to get to the same about of water then the other.

At its core it is the same understanding of the traditional understanding of the exposure triangle. It is the balance of 3 main values to obtain the mathematically correct exposed image. The bucket analogy is a different understanding of the same function to help people understand differently or better.The exposure triangle is the base of all exposures it allows for a photographer to gain a strong understanding of what creates an image and how to balance the three fundamentals of photography shutter speed, aperture and ISO to obtain a correctly exposed image.