Shutter speed, ISO, Aperture... oh my!

What is exposure? Exposure is a combination of 3 factors which determine the amount of light which enters your camera. These factors are aperture, ISO, and shutter speed. Photography is all about light, and without an ample amount of light entering your camera, you have nothing but a dark worthless picture. Learning how to determine the right combination of these three settings can be a tedious task, but understanding what they do will make it much easier.

Shutter Speed

Shutter speed is simply how long your camera's shutter stays open when you take a picture. These speeds can range from thousandths of a second to 30 or more seconds. The longer your shutter stays open, the more light your camera lets in. A shutter speed of 1 second lets in 4 times the light of a shutter speed of 1/4 second. The shutter speed can also determine the clarity of a picture. A longer shutter speed will blur the shot, and create trails from even the slightest bit of movement in your picture, whereas a shorter shutter speed will 'freeze' any action and create a sharp picture in which time appears to be stopped. For an example, take a picture of a constant drip of water using both a fast and a slow shutter speed. The shot taken with the slow shutter speed will create a soft blur of water, whereas the shot taken with the faster shutter speed will catch every individual drop in mid-air.
A fast shutter speed can also help eliminate blur due to camera shake when not using a tripod.

Aperture (f/stop)

Aperture (also known as f/stop) is how large the iris (or eye) of your lens opens up. A larger aperture means a larger opening in your lens for light to pass through. When referring to aperture, a smaller number is always a larger opening. For example, an aperture of f/5.6 is a larger opening, and therefore lets more light in, than an aperture of f/11. Each unit of measurement in aperture is called a 'stop' one stop up would be making the lens opening larger, and one stop down would be making it smaller. A single stop down of aperture lets half the light in that the previous stop did.
Comparison of the diameter of different f/stops.

Adjusting aperture also changes your Depth of Field. Depth of field is how much of the area, measuring away from your camera, is in focus. If you are tightly focused on an object which is relatively flat, you have short depth of field. If you are focused on a group of people standing at varying distances, you would need a long (or large) depth of field. Basically, a short depth of field (which would be caused by a large aperture) will be clearly focused on a relatively shallow area. The item you focus on may be sharp and clear, but any objects in the foreground or background may be blurred. A smaller aperture would create a larger depth of field, and bring all objects into perfect focus.
depth of field
depth of field

Film Speed (ISO)

Film speed (or ISO) is a measurement of how sensitive your camera's sensor (or in the case of a film camera, your camera's film) is to light. The larger the ISO (higher number), the more sensitive it is to light. The smaller the ISO (smaller number), the less sensitive it is to light. Each step up in ISO doubles the amount of light sensitivity (ISO 400 is 2x as sensitive to light as ISO 200). Using a higher ISO, you can sometimes get shots in low light that would have required a longer shutter speed or a larger aperture if you were using a lower ISO. However, this does not come without its setbacks. The higher the ISO is set, the grainier your picture will appear. At higher ISOs, you will notice some extremely substantial grain. ISO noise is much less noticable in DSLR and other large sensor cameras than it is in point and shoot cameras.
ISO comparison
ISO comparison

Camera Modes

There are several different 'modes' on your camera that determine the level of automation which your camera will provide. These modes are generally adjusted by a dial located on top of your camera, and may range from fully manual, meaning you have control over every single aspect of the shot, to fully automatic, meaning the camera will control everything for you based on the current conditions.

There are two categories (or 'zones') of modes, Basic (automatic) and Creative (manual), each of these zones make up half of the dial. Most dials have 'Fully Automatic' mode in the very center of the dial, marked by a green square. Basic modes are marked by icons which represent the primary use of that particular mode, and are generally accessed by turning the dial clockwise from fully automatic mode. Creative modes are marked simply by letters, and are generally accessed by turning the dial counter-clockwise from fully automatic mode.

Rebel XT mode dial
Rebel XT mode dial
Mode dial on the Rebel XT. Above the fully automatic mode is the creative zone, below it is the basic zone.===Basic Zone (Auto Modes)===
Modes which are typically located in the basic zone, but will vary depending on camera. Many cameras will not have all of these modes.
Pan Focus Mode - An assisted focus mode for shots in which there is a lot of movement or action, making focusing (either manual or auto) difficult. This sets the camera at the widest possible focal point to attempt to focus on the whole scene. (Not shown on example picture)
Portrait Mode - Icon: A side (profile) view of a head. - This mode brings subjscts in the foreground into sharp focus, and may enlist the use of a larger aperture to blur the background.
Landscape Mode - Icon: Mountains. - This mode is for taking shots of distant objects, or wide-angle shots, and will bring background objects more clearly into focus by setting a smaller aperture
Night Scene Mode - Icon: Icon containing a star. - This mode uses flash and a slower shutter speed to illuminate the subject and allow more light to enter the camera.
Black and White Mode - Used to take pictures in black and white, which is arguably not very useful, as you can always take a picture in color and convert it to black and white later using image editing software, which offers more versatility. (Not shown on example picture)
Macro Mode - Icon: Flower. - Used for extreme close-up shots where the camera may have trouble focusing in other modes.
Sports / Action Mode - Icon: Running person. - Use this mode for shots in which there is a good amount of motion which you want to capture without blurring.
Movie Mode - Used to shoot low-quality movie clips on point and shoot digital cameras (this mode is not available on DSLR cameras due to the method of action which they use). Mainly a novelty mode, it can not be expected to produce anything of worthwhile quality. (Not shown on example picture).

Creative Zone (Manual Modes)

Modes which are located in the manual zone, and offer greater control and fine-tuning of your shots
Program Mode (P) - Much like an automatic mode, the camera will still do the majority of work for you, but offers you the option to manually override settings such as focus, while the camera manages the exposure. Program mode is decent for beginners who want to be able to get quick shots without putting too much thought into it, but still want a bit more versatility than an auto mode offers
Shutter Priority (TV) - In shutter priority mode, you are able to manually adjust the shuter speed while the camera controls the aperture and ISO.
Aperture Priority (AV) - Aperture priority mode is similar to shutter priority mode, but lets you adjust the aperture, while the camera controls shutter speed and ISO.
Manual Mode (M) - This mode provides the most control of all, as you are able to adjust every aspect of the shot. There is absolutely no camera assist in this mode. You are able to adjust aperture, shutter speed, and ISO for yourself. Most experienced photographers will exclusively use manual mode due to the level of customization it offers.
Auto Depth of Field Mode (A-DEP) - A-DEP is a mode exclusive to Canon cameras, and will measure the depth of the nearest and furthest objects in the viewfinder when the shutter release is pressed half-way, and therefore is able to compose a shot with no blurring of the foreground or background objects which you focus on. A-DEP is complicated to use and generally not worth even attempting.

The primary things to think about when composing a photograph are your subject, your surroundings, and your positioning. Before taking a picture, ask yourself, 'What do I want to accomplish with this photograph?'. Create a goal or objective, plan it out, then make that plan work. There are two basic ways to do this; position your subjects, or position yourself.

A good way to teach yourself composition is to read up on the subject, then study others photographs, asking yourself questions such as 'What was the subject in this picture?', 'Did the photographer do a good job of making the subject the primary and immediate point of interest?', 'If not, what could have been done to change that?', 'Is the background visually pleasing, are there any distractions?'.

One good technique to get a feeling of what a scene would look like as an actual photograph is to make a frame out of your hands and view the scene through this frame. This effectively gives you a sense of border, and also blocks out items which may be otherwise distracting you from the actual scene at hand. Below is an example of this.
hand frame
hand frame
Viewing potential photographs through a 'hand frame' can give you a good feel for the end result.


All good pictures start with a subject. Before taking a picture, decide what you want the primary subject or point of interest to be. Generally, the picture should be taken in a way that makes the subject the first thing which is seen in the photograph. Your subject should be the primary point of focus and should be crisp and clear. Ideally, there should be nothing in the photograph that draws more attention than the subject itself. If, for example, you were to photograph a beach scene with a lighthouse as your subject, and a viewer is more drawn to a sandcastle on the beach, you've done a poor job of making your subject clear. Obviously, there can be, and many times are, multiple subjects in one photograph. In this case, the objective is to obtain harmony and balance between all subjects. Do you want them both to be equally attractive, do you want one to pop while the others are slightly more subtle? These are all questions which you must address, and plan accordingly. When choosing a subject, don't look at the photograph as the photographer, look at it as another photographer critiquing your work.


Frames can be basically any item that encloses or surrounds your subject. This could be branches of nearby trees or even a solid frame such as a cut-out in a wall. Take note of your surroundings, and keep an eye out for objects that would make for an image-enhancing 'frame'. Take shape, texture, and color into consideration, frames which contrast sharply with the subject of your picture can make for beautiful photographs. Use frames with care, as misuse can create cluttered or visually unappealing pictures.
Photographic Framing
Photographic Framing
A good example of framing, this picture would be rather bland without the frame. With it, however, it is a stunning picture. Photo by mnadi.


Obtaining the right balance between your subject and other aspects of the picture is extremely important. You don't want other parts of the photograph distracting from your subject. Things that you should pay attention to are color, contrast, size, and symmetry. Generally speaking, asymmetrical photographs are more appealing than symmetrical photographs. Placing your subject off-center usually has more of an impact and is more pleasing to the eye than having your subject smack dab in the middle, which brings me to the Rule of Thirds

Rule of Thirds

The Rule of Thirds is a photographic composition technique that most if not all advanced photographers employ quite a bit. The basis of this rule is that a photograph is divided into 9 equal sized sections, with 2 lines vertically and 2 lines horizontally. The four intersections of these lines are a good guidepoint for where your subject should be centered. These points (and lines also) also work as guides for other aspects of the photograph, for example, a horizon may look better when lined up with one of the lines. Also, when photographing people, a good use of the rule of thirds in many circumstances would be to line a person's body up with a vertical line, and line their eyes up with a horizontal line. This is likely one of the most important compositional techniques, as many photographers feel that a centered subject is not as interesting (in most situations). It is, however, recommended that you treat this 'rule' as more of a guideline though, as there are many circumstances where a more appealing photograph can be produced without the use of this rule. The rule of thirds goes all the way back to 1845, where it originated as a rule for composing scenic artwork.
Rule of Thirds
Rule of Thirds
A good example of employing the use of the Rule of Thirds in a landscape photo.