Langfords
pg 40
The light bending power of a lens is shown by its focal length. The focal length of a simple lens is the distance between the lens and a sharply focused image of an object at infinity (aka the horizon).
A lens with a long focal length has relatively weak bending power - it needs a long distance to bend light rays to a point of focus. The longer the focal length the larger the image.
A lens with a short focal length has stronger bending power.
The lens to image distance needed for sharp focus changes as the subject gets closer. The rule is: the nearer your subject, the greater the distance required between lens and film plane.
pg 58
The shorter the focal length, the smaller the image the lens produces.
A lens of short focal length used with a small format camera gives the same angle of view as a lens of longer focal length used in a bigger camera.
Angle of view - pg 57
The natural field of view of the human eye covers approximately 45 degrees and so a camera lens covering this angle is regarded as normal or standard.
pg 59
Changing the lens to a longer focal length (zooming to tele) makes the image detail bigger and the angle of view becomes narrower.
Any slight movement of the camera is also magnified.
Other changes include less depth of field for the same f number. A 100mm lens gives half the angle and twice the image magnification of a 50mm lens assuming distance subjects.
Changing to a shorter focal length (zooming to wide) gives more foreground and surroundings, everything is imaged smaller and there is greater depth of field.
Perspective - pg 61
Changing focal length together with your distance from the subject you exert a powerful influence on the perspective of your pictures.
Perspective is concerned with the way objects at different distances appear to relate in size and how parallel lines seen from an oblique angle apparently converge towards some far-off point.
The differences between two "heights" is in direct ratio to their distances from you. Perspective alters according to the distance from your viewpoint of the subject.
Steep perspective - close viewpoint plus wide angle lens or shortest focal length zoom setting. Exaggerates distance/height, dramatically emphasizes a foreground items.
Flattened perspective - distant viewpoint plus tele-photo lens or longest focal length zoom setting. Compresses space, makes a series of items one behind another appear "stacked up". In landscapes it helps to make background features dominate over the middle distance.
pg 40
The light bending power of a lens is shown by its focal length. The focal length of a simple lens is the distance between the lens and a sharply focused image of an object at infinity (aka the horizon).
A lens with a long focal length has relatively weak bending power - it needs a long distance to bend light rays to a point of focus. The longer the focal length the larger the image.
A lens with a short focal length has stronger bending power.
The lens to image distance needed for sharp focus changes as the subject gets closer. The rule is: the nearer your subject, the greater the distance required between lens and film plane.
pg 58
The shorter the focal length, the smaller the image the lens produces.
A lens of short focal length used with a small format camera gives the same angle of view as a lens of longer focal length used in a bigger camera.
Angle of view - pg 57
The natural field of view of the human eye covers approximately 45 degrees and so a camera lens covering this angle is regarded as normal or standard.
pg 59
Changing the lens to a longer focal length (zooming to tele) makes the image detail bigger and the angle of view becomes narrower.
Any slight movement of the camera is also magnified.
Other changes include less depth of field for the same f number. A 100mm lens gives half the angle and twice the image magnification of a 50mm lens assuming distance subjects.
Changing to a shorter focal length (zooming to wide) gives more foreground and surroundings, everything is imaged smaller and there is greater depth of field.
Perspective - pg 61
Changing focal length together with your distance from the subject you exert a powerful influence on the perspective of your pictures.
Perspective is concerned with the way objects at different distances appear to relate in size and how parallel lines seen from an oblique angle apparently converge towards some far-off point.
The differences between two "heights" is in direct ratio to their distances from you. Perspective alters according to the distance from your viewpoint of the subject.
Steep perspective - close viewpoint plus wide angle lens or shortest focal length zoom setting. Exaggerates distance/height, dramatically emphasizes a foreground items.
Flattened perspective - distant viewpoint plus tele-photo lens or longest focal length zoom setting. Compresses space, makes a series of items one behind another appear "stacked up". In landscapes it helps to make background features dominate over the middle distance.