Lenses and Focal Length

Transcription

1 Task 2 Lenses and Focal Length During this task we will be exploring how a change in lens focal length can alter the way that the image is recorded on the film. To gain a better understanding before you begin this task you will need to read to the text book information found on intranet. Pages and pages It is important that you read this information with the idea of developing an understanding of the concepts covered.

2 The Task Sheet It is important to read through the task sheet before you begin the work to establish what needs to be done and the order in which to do it. Task Lenses and Focal Length

3 Describing Lenses Photographers usually describe lenses by there focal length mm, mm (known as zoom lenses) Lenses of only 1 focal length are known as prime lenses. Common examples would be 24mm, 28mm, 35mm, 50mm, 105mm. Longer lenses with only one focal length are called telephoto. For example 500mm telephoto

4 Lens Characteristics Other lens characteristics are Lens speed This is determined by the maximum aperture opening of the lens. The wider the maximum aperture opening the faster the lens and the more light gather potential it has. Lenses of only one focal length are always faster than zoom lenses. Faster lenses are also more expensive. For example a 50mm lens with a maximum aperture of f2.0 may cost $200 but a 50mm lens with a maximum aperture of f1.2 may cost more than $1000.

5 What a Lens Can See The shorter the focal length of the lens (the lower the number eg. 18mm), the more of a scene the lens takes in and the smaller it makes each object in the scene appear. Often these lenses are known as Wide Angle Lenses. Of course the reverse applies as the focal length increases. Longer focal lengths eg. 200mm, result in less of the scene being taken in by the lens and objects also appear bigger.

6 How the Image Changes with Focal Length 300mm 200mm 150mm 100mm 50mm 18mm

7 Longer Focal Length Lenses As the focal length of the lens increases less of the scene is shown and what is visible is enlarged. Longer focal length lenses also compress depth giving the illusion that objects are closer together. The view on the top right was taken with a 50mm lens producing an image very close to that produced by the human eye. The objects in the scene are spaced apart as we would expect. The image on the right bottom was taken with the 300mm lens. The jetty in the foreground appears to be much closer to the gazebo.

8 Short Focal Length / Wide Angle Lenses Wide Angle lenses show more of a scene than human vision would. They also make objects appear further away than normal. Extremely wide lenses can create quite visible distortions, curving horizon lines and if used for portraits they can produce grossly distorted features. Wide angle lenses are excellent in confined spaces or when it is important to see a wide scene.

9 Short Focal Length Lenses in Use Lenses can be used to give some objects in a scene more dominance and as a result more importance. Photographers often do this on purpose, particularly if the photograph is advertising a product. Because they can be focused at very close range it makes the foreground objects look large in comparison to those in the background, whilst keeping everything in focus.

10 Zoom Lenses Zoom lenses are lenses that combine a series of focal lengths in one lens. They are usually larger and heavier than lenses of a single focal length. They have smaller maximum apertures than lenses of a single focal length although manufactures have steadily been working to improve this. The weight, size and limited aperture opening mean that the photographer must take additional care to ensure that the camera is held steady when taking photographs to avoid problems of camera shake. However in most day to day photography situations the convenience of the zoom lens makes it the most obvious choice of lens to use. Two or three zoom lenses can replace 6 or more fixed focal length lenses.

11 Choosing the Right Lens As a photographer choosing the correct lens is one of the important parts of the picture taking process. Developing an understanding about the way lenses work is one of the fundamentals to learn. This task, Focal Length and the next on Depth of Field will show you how to use the lens to control what you see in the photograph and then control what will be in focus. Using focal length and depth of field and important skills to understand for successful photography.

12 The Focal Length / Shutter Speed Rule To help you avoid Camera Shake problems use this simple rule - The slowest shutter speed that should be used when hand holding the camera should be equal to but not less than the focal length of the lens in use. Otherwise use a tripod or other device to hold the camera steady.

13 The Series of Focal Lengths to Use 200mm, 100mm, 18mm