Photography: How to Use the Diaphragm Aperture & Work Depth of Field
Photography & Light Regulation
Now a days, cameras are very complex devices with multiple functions and appliances that enable us to play and develop interesting effects, altering or capturing reality in unimaginable ways. Nevertheless, the first step in photography will always be to learn the basic principles of light regulation, and the mechanisms with which the photographer can modulate light to create the image he wants to compose.
There are 3 basic mechanisms within any given digital camera that serve the purpose of light regulation: the shutter, the diaphragm and the sensor sensitivity or ISO. This article is about the diaphragm: what it is, how it works and what can we as photographers achieve by working with and prioritizing it.
Photography for Everyone
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What is the Diaphragm of a Camera?
The diaphragm is a photographic device located in the lens of the camera, which regulates the aperture of the lens, thus regulating the amount of light that enters the camera. It is a disc, within the lens, that can open or close to different diameter values.
The more open the diaphragm is, the larger the diameter and the larger the amount of light that will enter the camera.
The smaller the diaphragm aperture is, the smaller the amount of light that will get to the image sensor.
Photo Example 1: Sunny Day, Diaphragm F8
Diaphragm Aperture and Focus Scale Diagram
How to Use the Diaphragm
Generally speaking, the idea is to counterbalance the atmospheric conditions we are working with. This means that when we have a lot of light, in sunny days for example, we use the camera’s mechanisms -in this case the diaphragm- to reduce the amount of light reaching the camera’s sensor (otherwise the photo would turn out too bright and colors as well as detail would be lost). In other words, if we want to take a picture in a bright sunny day, we would have to work with a small lens aperture or closed diaphragm.
The diaphragm aperture is measured in a “Focus” (F) scale that goes from F2 to F22, with F2 being the maximum aperture of the diaphragm, and F22 being the minimum aperture or the closest the diaphragm can be.
Remember it works kind of backwards: the larger the F number, the smaller the aperture, reducing the amount of light coming into the picture. The smaller the F number, the larger the diaphragm aperture and the bigger the amount of light we will be working with.
From a general point of view, a correctly exposed digital picture is a file that shows a full range of tones, from deep shadows to bright highlights, with detail across the entire image. You should see some detail in the dark shadow areas while at the same time retaining detail in the brighter highlight areas.
Photo Example 2: Diaphragm F5.6, Human Eye Perception
The Diaphragm and Its Photographic Effects
When prioritizing the diaphragm as a light regulator, besides determining the exposure or amount of light entering the image sensor, there are two additional effects we can create and work with: “Depth of Field” vs “Blur”, and “Chromatic Depth”.
What is Depth of Field?
The easiest way to explain the depth of field in photography is to tie it to the general sharpness of an image. When every item of a photograph, located at different focus distances, is sharp and focused, it is said to have a very high depth of field. If a photograph has some parts very sharp and others out of focus or blurry, it is said to have a low depth of field.
Having clarified this, the depth of field is defined as the "distance between the nearest and the farthest object in an image, which are considered to be well focused".
Photo Example 3: Closed Diaphragm, High Depth of Field
Photo Example 4: Open Diaphragm, Low Depth of Field, Blurry Effect
How does the Depth of Field relate to the Diaphragm and F Number?
- The closer the diaphragm aperture is, the higher the depth of field we will attain.
- The higher the F number, the higher the depth of field.
If we want to create an image where everything is correctly focused, including background, foreground, things at a close distance and things far away, we have to work with a closed diaphragm, which means F numbers from 6 onwards.
On the contrary, if we want to isolate a specific object in our photograph or create sharp & blurry contrast, we would have to work with an open diaphragm and low F numbers. In this case, we will achieve a sharp main focus and a blurry surrounding.
At F6 we start noticing the sharpness irregularities in the photograph, with some parts a bit out of focus; the lower the F number goes, the difference will be more and more obvious and the unfocused segments will become much more blurry.
If you want to create big focused/blurry contrast, work with two given objects that are relatively close to one another, this is when the effect becomes more obvious.
You´ll find more examples of this photographic effect and other useful tips to improve your technique, your photographs and your compositions in the following article: Nature Photography & Photography Tips.
Camera Used for these Photographs
All of the above photographs were taken with this Olympus Camera, which is a very compact SRL reflex professional camera, with a very good optic and a very practical, light design. Excellent for photographers that aren’t 100% dedicated to photography but never the less need high quality, professional photographs and can’t afford very high priced equipment; very good value for a very reasonable price.
Photo Example 5: How to Use the Diaphragm to Achieve Chromatic Depth
What is Chromatic Depth
When working with F values from 7 to 12, which means relatively closed diaphragm, there is another effect that comes into play, called “chromatic depth” (see diagram above).
Chromatic depth means that colors in the photograph will be saturated and become more intense, radiant, bright.
In other words, red will become RED, green will be GREEN, orange will be ORANGE! And so forth.
This color saturation is obviously more relevant to color photography but can also be noticed in black and white photography, where the different scales of grey will become more solid.
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