Photography Basics – Aperture, Shutter Speed & ISO

1/6th sec @ f22

1/6th sec @ f22

Welcome to the first in a series of Photography tips aimed at beginners to photography and photographers who have a basic understanding but with to improve their creativity.

I decided to write this as a result of comments online that many DSLR owners used their camera as a fancy point and shoot, when I asked around it was apparent that some people who are new to photography may not have an in-depth knowledge of their camera controls or the basics of photography and that a few simple tutorials may help them to achieve their potential.

I’ll start with the basics as they have the most impact on what we all do in general and also have the most creative impact on an image, that is Aperture, Shutter Speed and ISO.

Aperture

The aperture determines how much light passes through the lens, it is basically a diaphragm that can let in varying amounts of light, similar to the iris in your eye. Fully open and it will let in more light, reducing the aperture size will let in less light, but that is not all the aperture does it also affects the Depth of Field (Dof) in the final image.

DoF is the amount of the image that is in focus on the focal plane, this is basically the point where your sensor (or film) is placed. With the aperture wide open the DoF will be shallow, the portions of the image closer and further away than the main subject will be out of focus and blurred, with the aperture stopped down more of the image will be in focus.

The location of the aperture control on your camera will vary but it will be used to adjust the f-stop or f-number, this number is the ratio of focal length to effective aperture diameter, but a smaller f-number (f3.5) equates to a wider opening and more light / less DoF, a larger number (f16) equates to a smaller opening and greater depth of field.

The actual range of f numbers will vary dependent on the lens in use and you may notice that a zoom lens will have two maximum f numbers i.e. f3.5 – f5.6 which relates to either end of the zoom, finally each change in f-number is one stop or Exposure Value (Ev) in light (remember this it will come up again later).

Shutter Speed

The shutter determines how much light hits the film or sensor, or more accurately, the length of time the sensor or film is exposed to the light entering the camera. On the old wooden plate cameras this was as simple as a wood or metal slide that the photographer would pull out from the film holder and replace after a matter of minutes had passed, as film became more sensitive, the shutter became more advanced offering higher speeds and has now evolved to a series of mechanical blinds in front of the sensor (or film) which open for a fraction of a second to allow light to hit the sensor.

Speeds can range from several seconds to a maximum of several 1000’s of a second i.e 12 s – 1/8000. Shutter speeds also traditionally increase in the following form 1/125, 1/250. 1/500 etc. each increase or decrease in shutter speed related to 1 Ev in light (I said it would come up again).

Again shutter speed has another use, a high shutter speed can be used to freeze motion, that’s great right? We all want the subject to be sharp, right? Well yes, and no. There may be times when you want to convey motion, how do you do this with a subject (or medium) that is static, well by introducing a degree of blur.

Sports photographers will often use a slower shutter speed(1/60th) and pan the camera with the action, when done right this will give a sharp subject but the background will be blurred, a lens can be zoomed during a long exposure to give a creative blur or the motion of a waterfall can be conveyed by turning the appearance of the water into a smooth, silky fog by using exposures longer than 30 seconds.

ISO

ISO is traditionally a rating of how sensitive film is to light, different films would have a different rating i.e. ISO 50, ISO 100, ISO 200, ISO 400 the lower the number (ISO 50) the less grain the film has so it produces a sharper image but is less sensitive to light so needs brighter conditions or a tripod, the higher the number (ISO 400 or even ISO 3200) gives a much more grainy image with possible colour shifts  but will allow you to shoot in lower light.

For example taking ISO 100 as standard; an exposure of f8 @ 1/250 at ISO 100 equates to f8 @ 1/125 at ISO 50 or f8 @ 1/4000 at ISO 3200.

So has the advent of digital cameras made ISO irrelevant? No of course not.

Your DSLR will still have an ISO dial, it will vary between ISO 100 to ISO 3200 on average, and guess what? Each step up or down in ISO equates to 1 Ev (you were paying attention to that – right?).

So what does this mean? Well, in general the Lower the ISO the better. A digital sensor works by converting the light that hits its surface into a digital signal, increasing the ISO increases the sensitivity of the sensor by increasing the electric charge across it, whilst this will allow the camera to work in darker environments it will also introduce noise (or grain) into the image, which can result in a degeneration of image quality. Sometimes, however you may need to sacrifice a little bit of image sharpness to get the shot, indoors at a concert or sporting event the lighting may not be bright enough without increasing the ISO, or you may want to use grain creatively.

The Exposure Triangle

Now, if you remember what I wrote earlier there is a common point: each increase or decrease of Aperture, Shutter Speed and ISO increases or decreases the Ev by one stop, therefore a combination of these values will give a correctly exposed photo but with varying effects. If you want just a small part of the image in focus a wide aperture will achieve that but will require a high speed, if you want more of the image in focus use a smaller aperture but you will need a slower speed, this is the basics of making a manual exposure (that funny M symbol on the camera settings).

Most Cameras will have at least a program (auto) mode, Aperture Priority mode and Shutter Priority Mode. Program will do a decent job at getting a well exposed image, but use the other modes and play. Taking a portrait? Open the aperture a bit (to f3.5 for example) and throw the background out of focus. Shooting a landscape? Close the aperture down more (to f11 or f16) and pack the frame with front to back sharpness. At a sports event? Set the camera to Shutter Priority and use a high speed (1/500th ) to freeze motion or use a slower Shutter Speed and deliberately add blur to emphasise movement.

Photography, as in life has rules; rules to get the right exposure, to freeze motion, to obtain the most pleasing composition. I would urge everyone to learn the rules and learn when to apply them for best effect, in this way the technical aspects of photography becomes second nature and will allow the photographer to concentrate on the creative aspect of photography. But just as importantly, or more importantly, knowing the rules means that when you deliberately break them, you know why you have done so, you will have done so for a creative reason, but you will also know how to reproduce the effect when you need to.