THURROCK Camera Club, which is rapidly approaching the celebration of its centenary, has just held its final competition of this season.

This was the inaugural triptych competition in honour of one of the club's committee members, Chas Taag, who passed away suddenly just prior to Christmas last year.

The concept is to produce a triptych image that presents three images with a common theme in a single photograph.

The top three places awarded by the judge were:

• Winner was Mel Fox - Poinsettia

• 3rd Dave George - Cactus in Flower

Meanwhile, in the latest of our series of photographic tips from club members as the clock ticks towards the centenary celebrations , in this article we look at another important element that photographers need to consider when capturing their images, Depth of Field (DoF).

Having an understanding DoF and knowing what factors may impact it is an important skill for photographers to develop.

The ability to understand and apply your desired depth of field will enable you to produce images that will allow your main subject to stand out from the background or produce the blurred backgrounds you often see in professional photographs or alternatively ensure that everything you want to capture in your images is in reasonable focus.

What is Depth of Field?

Depth of field is described as the distance between the closest and farthest objects or part of the scene in a photo that appear in sharp focus.

Simply explained, when we adjust the camera's lens to focus on a subject it will only achieve perfect focus at one particular distance; anything in front or behind this point will be blurred to a greater or lesser degree. However, the transition from sharp to unsharp focus is gradual and can be controlled by the photographer, most commonly by one or all of the following three things:

1. Lens aperture diameter – (The F-stop you have used on the lens)
2. Focal length (i.e. the optical distance (usually measured in mm) from the point where the light meets inside the lens to the camera's sensor.)
3. Distance from the subject and the distance of the background behind the subject.

The most common way that photographer's control depth of Field is via an adjustment to the lens aperture. By increasing or lowering the lens aperture (adjusting the size of the opening of the hole inside the lens) you will control the amount of light that will reach the camera's sensor, similar to a pupil in your eye, which dilates to let more light in or can contract to restrict light when it is bright.

That said, what may be counter intuitive for some, is that larger lens apertures, which correlate to smaller f-stop numbers, let in more light and produce a very shallow Depth of Field. On the other hand, small apertures, or large f-stop numbers, will restrict the amount of light entering the camera, producing images with a large Depth of Field.

Focal length measures the distance, usually in millimetres, between the optical centre of the lens and the camera's sensor. It is determined when the camera is focused to infinity. Lenses are named by their focal length, and you can usually find this information on the barrel of the lens. For example, a 50 mm lens has a focal length of 50 mm.

To explain how this feature impacts your image, the Focal length describes the angle of view captured by a lens, i.e. how much of a scene the lens will capture and how large subjects within the frame appear.

The longer the focal length of a lens, the narrower its angle of view so the less of the scene will be captured and this is what allows you to get close up images from distance e.g. using a telephoto lens.

Finally, we can look at distance to the subject. The closer the subject is to the camera, the greater the relative distance from the front to the back of that object. A high relative distance gives a corresponding reduction in how much of the object appears in focus. In other words the further away the background of your image is to the main subject the more likely it will be to be out of focus.

By attaining an understanding of Depth of Field, you can decide which parts of your photograph you wish to have in focus and which elements you wish to be blurred. The decision will be governed to a certain extent by the subject matter of your image, but having a grasp of basic DoF principles will enable you to decide how you wish your image to appear.

It is possible to obtain tools to help measure exact DOF for images, but by of a simple rule of thumb guide it may be easier to remember the following.

To Increase Depth of Field:

• Select a narrow aperture
• Shorter focal length
• Move away from subject

• Use a Wider aperture
• Seek a Longer focal length
• Move closer towards subject

In the attached examples you can see how different approaches to the Depth of Field have impacted the images.

In the image, "Artificial flowers", the photographer has chosen a depth of field that slowly softens the background of the image. This allows him to capture sharp detail on the foreground blooms but softens the flowers towards the back of the image, while still retaining their shape so they can be identified as part of the plant.

In the image entitled "Biker" the author has utilised a very shallow depth of field by applying a wide aperture which has enabled him to blur the background to the subject. This avoids the intrusion of any potential distractions to the subject and also helps the face of his subject stand out.

In the final image, "Twilight at Corbiere" given the distance to the main element of the images, the lighthouse and rocks, the photographer has employed a smaller aperture to maximise his depth of field in order to capture a larger amount the scene that is in focus for the viewer.