Explaining All The Parts Of A Zoom Lens


The lenses that are used on most professional video camcorders are zoom lenses. This means that the focal length can be altered while filming to change your composition, a process called 'zooming'.

The requirements for professional lenses are very high to make sure that the picture is never deformed during the complete zoom range. The lens design is very complex and sophisticated. It's characteristics are the most important influence on the impact of an image.

Zoom range

A lens is usually defined in the following way: zoom range X minimal focal length. The minimal focal length tells us if a lens is a telelens or a wide angle lens, usually the separation is at about 7.5 mm. Click here to learn more about focal lengths. Some studio lenses can go both very wide and still have a large zoom range. These lenses can be used for a almost all situations.

A zoom lens allows faster working methods than using prime lenses. Sometimes it is easy to forget which focal length you are using while filming.

Back-focus

The flange focal-length adjustment ring controls the back-focus lens, which makes sure that your subject stays focussed while zooming. This setting is known as the back-focus setting, and it should be correctly set up when preparing your camera, or when changing lenses.

A good lens is designed to keep your subject focused throughout the whole of its zoom range. However, to make sure this is the case, the back focus has to be correctly adjusted. If you zoom in on your subject, focus, then zoom out and you discover that the picture looses sharpness, your back focus has not been properly set up or has been changed during production.

See Setting up the back-focus to learn how to properly set up the back-focus of your lens.

Macrolens

In the lens is also a macrolens that can be used to create shots very close to your subject, closer than the Minimum Object Distance (MOD). To use this part of the lens, pull the safety knob on the macrolens ring, and then you can turn it. The safety knob is used to make sure you don't accidentaly turn the macrolens ring while filming, as this will make your regular shots very out of focus.

The focusing ring

The focusing ring is used to make sure your subject is in sharp focus. You can choose to control the ring yourself (Manual), or by a servo motor (Servo) by setting the zoom selector. The sharpest focus can be checked before shooting by rocking the focus point behind and in front of your subject.

The zoom ring

The zoom ring allows you to change the focal length to adjust the image size without moving the camera position. It also can be controlled manually or by a servo motor. The zoom ring is generally used in three ways, to compose a shot, to readjust the composition of a shot and to change the shot size while shooting.

The aperture ring

The aperture is referred to the lens diaphragm opening inside the lens. The size of the diaphragm opening in a camera lens regulates the amount of light that passes through onto the camera sensor. The aperture ring is the prime method of controlling exposure. This can be done manually or automatically (using auto-exposure, or remotely).

Extender

Some lenses are fitted with an extender, which alters the range of focal lengths. An extender optically enlarges the image coming through a lens. Most of the times using an extender affects the picture quality in a bad way.

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