Understanding the camera lens

The lens focuses light on to the film to form an image, and unless that image is sharp you will never produce clear pictures. So it is important to understand how the lens works, and what your particular lens can do. Only when you feel comfortable with the lens controls and can adjust them quickly and accurately will you get the most enjoyment and satisfaction out of trying out different effects in photography.

Focal Length

The amount of a scene photographed by any lens is governed by its focal length. On a 35mm camera a normal lens of 50mm has roughly the same view as the human eye. To photograph more of the subject, or to pull distant objects closer, you need lenses with different focal lengths.

The shorter focal length (under 35mm) of the wide angle lens gives a broad view of the scene, while the much longer focal length of a telephoto lens shows up detail in distant objects.

Look at the below example, the same subject shot with a wide angle 16mm lens and a telephoto 200mm lens.

16mm vs 200m

Focal length is the distance between the lens and the film when the lens is focused at infinity (for a normal lens, that means set for objects more than 30m away). You can set fire to a piece of paper by holding a magnifying glass at exactly the point where a sharp image of the sun (at infinity) forms on the paper, and a camera lens focuses an image on film in the same way. In each case, the distance between the lens and the image is the focal length.

Now imagine a magnifying glass forming the image of a candle flame on a sheet of paper. The distance between paper and glass before a sharp image is formed is greater than when the sun’s rays are used. The closer an object is to the camera, the further the lens must be from the film to focus correctly. Most simple 110 and 126 cameras have lenses with no focusing adjustment. These have been factory set to keep everything sharp between 2m and infinity. Most 35mm have lenses which must be accurately focused by the photographer. These are set up in helical mounts, two telescoping tubes with a screw thread between them. The closest focusing distance is determined by the maximum movement of this mount: for example, the shortest distance a 50mm lens fitted to a 35mm reflex camera focuses at is usually about 50 – 70cm.

If you have a reflex camera, try this yourself by setting the lens to minimum distance and moving backwards and forwards until an object close by becomes sharp in the viewing screen. Then measure the distance in between.

Aperture

Brightness control

The brightness of the light reaching the film is controlled by a hole called the aperture. It works like the pupil of the eye, large in the dark to let in more light and small in bright conditions. The camera lens controls its aperture with a diaphragm (a mechanical iris) which is operated by a ring or lever outside the lens. The dimmer the light the larger the aperture must be to keep the brightness of the light on the film constant.

F  numbers

Simple cameras often mark the aperture control with weather symbols, but the more complex cameras use a numerical system called f numbers. The smaller the f number, the larger the aperture: for example, f2.8 lets in more light than f5.6 and much more than f16.

Depth of field

Changing the f number also affects the depth of field, or amount of the scene in front of the camera that appears in focus. The depth of field scale on the lens indicates how much of the area in front of and behind the subject is in focus. If you move the aperture ring on the lens through the range of f numbers you can see how this control over sharpness can be used to subdue unwanted background and emphasise the main subject or, at a smaller aperture, to take a picture which is sharp from the foreground to infinity.

The full range of lenses

There are a wide range of lenses currently available. The photographer has to choose the focal length that he needs for a particular subject. The 28mm, 50mm, and 135mm focal lengths used on cameras which take interchangeable lenses cover most situations. Beyond these there are the ultra-wide angle (below 28mm) and long telephoto (over 200mm) lenses for special effects. These special lenses and the equipment for close-up photography, zoom lenses, and mirror lenses are discussed in later chapters.

The wide angle of view of a 20mm lens gives great depth of field, which means that most of the picture is sharp and focusing is not critical. Distortion of the subject at the edge of the lens must be taken into account. Lenses as wide as the 8mm fisheye are not corrected and the result is a completely circular view with only the centre of the picture retaining familiar proportions.

Powerful telephoto lenses – such as 1000mm lenses – show detail in distant subjects which, pictured on their own, look normal. If other objects are included in front of or behind the subject, distance appears compressed. As focal length increases through the lens range, the depth of field shortens dramatically and accurate focusing is essential to get a sharp result. These long lenses are large and heavy so a tripod should be used to avoid camera shake.

Prime Lenses vs. Zoom Lenses

Prime lenses have a fixed focal length. Basically, when you look through the viewfinder, the image you see, that’s as ‘zoomed in’ or ‘zoomed out’ as it goes. If you want to get more or less of the scene in the frame, you have to move your feet to physically recompose the shot.

Zoom lenses have the ability to zoom in and out. So you can stay in one spot and use the lens to recompose the shot.

Most photographers have a collection of lenses that they use for different purposes. Prime lenses, which have a fixed focal length, are typically used for portrait or close-up photography, while zoom lenses, which have a variable focal length, are better suited for landscape or action shots. Each type of lens has its own advantages and disadvantages. Prime lenses are usually sharper and produce less distortion than zoom lenses, but they can be more expensive and less versatile. Zoom lenses are more affordable and offer more flexibility, but they may not produce as high-quality images as prime lenses. Ultimately, the best lens for a particular situation depends on the photographer’s needs and preferences.

Image stabilisation

Some cameras have this built into the camera itself, in other cases, the stabilising part of the camera is in the Lens.

Image stabilisation, also known as stabilization or vibration reduction, is an important element of photography that helps to reduce the effects of camera shake. This is particularly useful in low-light situations, where hand tremors and subtle changes in lighting can lead to unwanted blurring in photos. There are a variety of different image stabilisation technologies out there, ranging from simple image sensors placed on the camera body to sophisticated integrated lenses with electromagnetically controlled internal mechanics. Whatever the type of image stabilisation system used, however, it essentially works by offsetting the tiny movements caused by your hands and arms as you take your shot. The result is smooth, blur-free images that capture even the smallest details with clarity and precision.

Lens Filters

When it comes to photography, one of the most important tools you can use is a lens filter. Why? because it acts as a very cheap way of protecting the exposed bit of glass at the front of your lens. I’ve chipped a few of my lenses, all I needed was a cheap UV filter on the end and that would have cracked instead, saving me a large repair bill. Lens filters act as an add-on to your camera, providing a range of different effects that can enhance your photos and help you capture the types of shots you’re looking for. There are a number of different types of lens filters, including neutral density (ND) filters, UV filters, graduated neutral density (GND) filters, and polarizing (PL) filters. Each type has its own unique characteristics and properties that allow you to customize your photos according to your specific vision or creative goals. Whether you’re looking to achieve vibrant colours or pristine highlights in bright sunlight, there’s a lens filter that can help you achieve the results you’re after. So if you’re looking to take your photography skills to the next level, consider adding a lens filter to your arsenal and start experimenting with all the possibilities they have to offer!

UV filters – filter out UV light rays, but they’re mostly used for lens protection

Neutral density filters – the sky and the ground are different brightness levels, neutral density filters help you even out the brightness so you can get an accurate exposure of a whole scene.

Polarising filters – reduce/eliminate reflections from glass and water, also increased colour saturation