Posts Tagged 'Depth Of Field in Digital Photography'

Aperture in Photography

Aperture in Photography

Part 1

Last week I discussed Shutter Speed as one of three factors to control exposure. For this week’s new series of articles I am going to cover the basics of Aperture.

What is Aperture? 

Let’s take a look at a definition of aperture from Wikipedia:

In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane. If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. If an aperture is wide, then uncollimated rays are admitted, resulting in a sharp focus only for rays with a certain focal length. This means that a wide aperture results in an image that is sharp around what the lens is focusing on. The aperture also determines how many of the incoming rays are actually admitted and thus how much light reaches the image plane (the narrower the aperture, the darker the image for a given exposure time). In the human eye, the pupil is the aperture.

An optical system typically has many openings, or structures that limit the ray bundles (ray bundles are also known as pencils of light). These structures may be the edge of a lens or mirror, or a ring or other fixture that holds an optical element in place, or may be a special element such as a diaphragm placed in the optical path to limit the light admitted by the system. In general, these structures are called stops, and the aperture stop is the stop that determines the ray cone angle, or equivalently the brightness, at an image point. In some contexts, especially in photography and astronomy, aperture refers to the diameter of the aperture stop rather than the physical stop or the opening itself. 

Sounds pretty complicated, right? But stay with me! In this series of articles I am going to cover the practical uses of aperture in photography rather than the scientific explanations.  In general terms, and for all types of photography, the aperture is the unit of measurement that defines the size of the opening in the lens, which can be adjusted to control the amount of light reaching the film or digital sensor. The size of the aperture is measured in f-stops.

Aperture in Photography

Aperture is a measurement unit for the opening of a lens.

In its most basic role the aperture controls the volume of light passing through the lens. As you can see in the above diagram, the lower the number (f-stop) the larger opening, which allows more light to pass through; the higher the f-stop, the narrower the opening, with less light coming through the lens.

How/where do I change the Aperture setting?

In modern digital cameras, you can control the aperture’s f-stops through camera body. If you set your camera to Aperture Priority (A, or AV), you set the f-stop by using the main command dial and the camera will then select the correct shutter speed and/or ISO to adjust the exposure.

In these photos I used different f-stops (high number/narrow opening and low number/wide opening); because I was in Aperture priority mode the camera adjusted the exposure by changing the shutter speed.

Aperture in photography

In Aperture priority mode you select the f-stop and camera selects the correct shutter speed or/and ISO

Aperture in photography

Aperture in photography controls the volume of light passing through the lens

This concludes the basic look at what aperture is and does. Stay tuned for Part 2 where we’ll look at some creative uses for aperture settings.

Ted and the Omnilargess Team

Check our upcoming and new digital photography classes

0
Depth Of Field in Photography

Depth Of Field in Photography

How does aperture control Depth Of Field

Aperture is one of the main controls in photography. As you know we can set our exposure by using Shutter speed, ISO, and Aperture. But controlling exposure is not the only important performance of the aperture. Another significant role is to control the Depth Of Field.

What is Depth Of Field?

I found the best description for depth of field in Wikipedia:

In optics, particularly as it relates to film and photography, depth of field (DOF) is the distance between the nearest and farthest objects in a scene that appear acceptably sharp in an image. Although a lens can precisely focus at only one distance at a time, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under normal viewing conditions.

In some cases, it may be desirable to have the entire image sharp, and a large DOF is appropriate. In other cases, a small DOF may be more effective, emphasizing the subject while de-emphasizing the foreground and background.”

Although it may seem complicated, in real life application it is not. As a rule of thumb the higher f-stops (higher the number) give greater depth of field, with more of the scene appearing to be in focus in your photo. And vise versa, a lower f-stop results in a smaller (shallow) depth of field, with only one sharp and focused point in the image.

There are several other rules which apply to depth of field, such as lens focal length and the size of your media (sensor or film), which I will discuss in a different article.

For these photos the camera was on a tripod, ISO 200, Aperture Priority mode.

DSC_1407

A shallow Depth Of Field by using lower f stop (f2.8)

By using higher aperture value (f22), you can increase the Depth Of Field

By using higher aperture value (f22), you can increase the Depth Of Field

You see that as I opened up the aperture (set f-stop to a lowest number) the background and foreground go out of focus. It is a simple and effective technique to ensure your main subject is noticeable to viewers at the first glance.

Shallow Depth Of Field is very useful for portraits

Shallow Depth Of Field is very useful for portraits

On the other hand some time you want to keep everything in the scene in focus, then you need to use a value for aperture (f22 and higher)

Larger f stop means longer Depth Of Field which brings everything from foreground to background to focus. Very useful for Landscape Photography

Larger f stop means longer Depth Of Field which brings everything from foreground to background to focus. Very useful for Landscape Photography

 

If you want to learn more Register for our Understanding Exposure in Digital Photography workshop on May 22, and 23. Class size is limited.


Ted and Omnilargess Team

0