Exposure of a photograph is the balance between light and dark tones of the environment to provide contrast and clarity sufficient to composition. To adjust this balance, the photographer blocks and controls the ambient light through your camera + lens.
Without considering the use of photographic filters, exposure depends on three basic configurations of the camera and photographic lens (which will be explained further on in the text):
Opening of the diaphragm of the lens (f-stop);
Exposure time (time that the camera shutter remains open);
These settings can be adjusted to balance the light captured by the sensor (digital camera from A2zCameraBlog) or film (in analog camera).
Understand how these three elements interact is the first step to stop using the camera’s automatic exposure mode and start using the manual exposure mode. When using the manual mode, the photographer gains the ability to use your creativity by choosing the depth of field you want, beyond the level of grain/noise and the amount of movement and blur.
This article is recommended for beginners in photography who want to someday, “exit” and also for established photographers who want to recall some basic concepts related to the exhibition.
What Is The Triangle Of Photographic Exhibition
The triangle of photographic exhibition is a graphical representation of the three main factors that affect the exposure of a photograph, one at each vertex (or tip):
The camera’s manual mode, the adjustment of each of these parameters can be done independently, giving creative freedom to the photographer to change deeply not only exposure, but also to yourcomposition.
Each balancing makes the same scene can be captured with different configurations, and yet the image is well exposed.
As Elements Of The Triangle Of Exposure Affect The Photo
To explain visually, the triangle has been modified and demonstrates how each of the three main elements influence the exposure of a photo:
The more open the diaphragm of the lens, the more clear it is photography;
How much longer is the exposure time, clearer is photography;
The higher the ISO sensitivity, the more clear it is photography.
Conversely, the more closed the diaphragm is, the shorter is the exposure time and the lower the ISO sensitivity, darker is the final image.
Now Look At Each Of The Three Variables Individually:
Exposure time of the photo
The variation of exposure time affects the picture as follows:
When the exposure time drops by half, only half the light that would be captured by the camera reaches the sensor or film. The other half is blocked by the closed shutter. Because of that, the image would be darker *.
* This statement is only valid if the opening of the diaphragm and the illumination available remain constant.
If the intention is to keep the exposure of a photograph unchanged, to modify the exposure time to see how to proceed with the examples below:
If the exposure time is reduced to half (only half the light reaches the sensor or the photographic film), then the ISO needs to be double to compensate for the lower entrance light, or the diaphragm (f/stop) you need to have your opening folded area (stay open a stop).
If the exposure time is doubled, so the ISO sensitivity needs to be cut in half or the diaphragm needs to close a stop to compensate.
Cause And Consequence Table For Enlarging And Reducing The Exposure Time:
|Action (Cause)||Consequence 1||Result 2|
|Decrease exposure time||Photo darker||Photo “frozen”-moving objects are in perfect focus|
|Increase the exposure time||Photo lighter||Photo with sense of movement – moving objects are stained|
See The Following Two Examples Comparing Long And Short Exposure Time:
Pictured left: short exposure time (1/1000 seconds) – movement of frozen birds;
Pictured right: long exposure time (6 seconds) – water movement emphasized.
The variation of f/stop changes the exposure of the photo as follows:
When the diaphragm is closed in one stop, only half the light that would be captured by the camera reaches the sensor or film. The other half is blocked by the diaphragm. Because of that, the image would be darker*.
* This statement is only valid if the exposure time and the lighting available remain constant.
If the intention is to keep the exposure of a photograph unchanged, to modify the opening of diaphragm, see how to proceed with the examples below:
When the diaphragm is open a stop, your area of opening is folded and double the light passes into the camera-so, the exposure time or the ISO sensitivity must be reduced by half to compensate.
And when the diaphragm is closed in a stop, your area of opening for the passage of light is reduced by half – so, to compensate, the exposure time or the ISO sensitivity have to bend.
Below is a video showing the camera taking pictures with different openings:
Table of cause and consequence for opening and closing the diaphragm(1):
|Action (cause)||Consequence 1||Result 2|
|Close the diaphragm||Photo darker||Greater depth of field|
|Open the diaphragm||Photo lighter||Less depth of field|
(1) This table indicates consequences of increasing or decreasing the aperture diaphragm while the ISO sensitivity and exposure time are kept unchanged and available lighting is constant.
See the following two examples comparing different extremes of f/stop:
Pictured left: f/stop down (f/2.8)-selective focus (only part in focus)-depth of field is less;
Pictured right: f/stop (f/9)-even with different planes of distance in the landscape, everything is in focus-depth of field greater.
The following illustration shows the relationship between different openings and the depth of field in photography.
ISO sensitivity variation changes the exposure of a photograph as follows:
When the ISO sensitivity is doubled, the picture becomes clearer, as if the light had twice hit the sensor or film. The inverse is also true: If the ISO sensitivity is reduced by half, the image becomes darker, as if only half of the light had hit the sensor or film.
If the intention is to keep the exposure of a photograph unchanged, to modify the ISO sensitivity, see how to proceed with the examples below:
When the ISO is folded, the exposure time or the opening of the diaphragm should be reduced by half (reduction of a stop).
When the ISO is reduced by half, to compensate for the lower light sensitivity, exposure time or the opening of the diaphragm should be bent (one stop).
As an example of the above, the following video shows the camera set the aperture priority mode (A) with the opening of the diaphragm set at f/11. While the ambient lighting remains constant, the exposure time varies according to the ISO being modified.
Table of cause and consequence to increase and decrease the ISO sensitivity:
|Action (Cause)||Consequence 1||Result 2|
|Increase the ISO sensitivity||Photo lighter||Photo with more noise or graininess and sharpness, richness of colors, contrast and dynamic range|
|Decrease ISO sensitivity||Photo darker||Photo with less noise or graininess and sharpness, richness of colors, contrast and dynamic range|
The following is an example of digital photography with high ISO. Note the presence of noise and how not so sharpness, richness of colors, contrast and dynamic range.
Photographic Filters And Your Influence On The Exposure Triangle
Photographic filters are usually used to control the entry of light into the camera and/or the white balance of an image and therefore modify significantly the exposure of a photograph.
Without going into too much detail, the polarizing filters, neutral density and infrared are those that have the most power to influence the exposure of an image (ultraviolet (UV) Filters and skylights also influence the exposure of an image, but with less power). Due to your ability to absorb ambient light, these filters block the passage of light into the camera.
The graph below demonstrates just how adding a filter makes the image darker, if none of the three elements of the triangle of exposure changes.
To block a portion of the light would go on camera, filters, therefore, require that photographers make adjustments to one or more of the three elements of the triangle of exposure to compensate for “loss of light”.
The options to make the photo more clear are: increase the exposure time and/or the opening of the diaphragm and/or ISO sensitivity.
The polarizing filter absorbs part of the luminosity and leaves only polarized light waves in a particular direction to the sensor. In this way, is controlled the entry of unwanted light on the camera.
By controlling the passage of unwanted light, the exposure of the image becomes darker, which allows the photographer to increase the exposure time and thereby increase the saturation of the image.
→ For a full article and more information, visit our page of *polarizing filters.
Neutral Density Filter (ND)
The neutral density filter absorbs by equal a percentage of all waves of light, of all colors, to go through it and follow to the sensor.
These filters are like sunglasses to the camera lens.
When using a neutral density filter, the amount of light that passes into the sensor decreases. This allows the photographer to increase the exposure time or open the diaphragm without the photo be overexposed.
→ For a full article and more information, visit our page of *neutral density filters.
The infrared filter blocks the entire spectrum of visible light to the naked eye, leaving only infrared radiation pass the environment into the camera.
To compensate for light blocking size, images created with the aid of infrared filters are usually (very) long exposure. For example, even on a day of bright sunshine, the photographer may need more than 30 seconds of exposure for your photo be well exposed.
Checking The Exposure Of The Photo With A Histogram
A way to verify that the choices made for the three elements of the triangle of exposure are correct is to analyze the histogram of the picture. Most digital cameras have the option to display the histogram on the screen even before the shutter releases, while in other models the histogram can only be verified after the picture was clicked.
Note: compact cameras generally do not show the histogram on the screen.
In A Few Details, The Histogram Lets You Analyze The Picture:
Is underexposed-the graph is disproportionately more to the left;
Is superexpostra – the graph is unbalanced especially to the right;
Lost detail/texture/information to be extremely under or overexposed.
The following are three examples of the same photo: with the perfect exposure, underexposed and overexposed. Notice how change the histograms of each version.