# Determining Focal Length

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In summary, focal length refers to the distance between a camera or telescope lens and the image sensor or film when the subject is in focus. It is measured in millimeters and is determined by the curvature of the lens and the distance between the lens and the sensor or film. The focal length also determines the field of view, with shorter focal lengths resulting in a wider field of view and longer focal lengths resulting in a narrower field of view. Focal length varies among lenses, with prime lenses having a fixed focal length and zoom lenses having a range of focal lengths. Focal length is important in photography and optics as it affects perspective, depth of field, composition, and the magnification and clarity of the subject being captured.

## Homework Statement

Without her contact lenses, Kat cannot clearly see an object more than 70.0cm away. What should be the focal length of her corrective contact lenses?

1/f = 1/p + 1/q

## The Attempt at a Solution

1/f = 1/infinity + 1/-70.0cm = -0.0143cm
f = -70.0 cm

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Your attempt at a solution is correct. The focal length of Kat's corrective contact lenses should be -70.0 cm. This means that the lenses have a negative power, which is common for corrective lenses used to correct nearsightedness (myopia). Good job using the thin lens equation to solve this problem!

## What is focal length?

Focal length refers to the distance between the lens of a camera or telescope and the image sensor or film when the subject is in focus.

## How is focal length measured?

Focal length is measured in millimeters (mm) and is determined by the curvature of the lens and the distance between the lens and the sensor or film.

## What is the relationship between focal length and field of view?

The focal length of a lens determines the field of view, or how much of the scene can be captured in the image. A shorter focal length results in a wider field of view, while a longer focal length results in a narrower field of view.

## Is the focal length the same for all lenses?

No, the focal length varies among different lenses. Prime lenses have a fixed focal length, while zoom lenses have a range of focal lengths that can be adjusted.

## Why is focal length important?

Focal length plays a crucial role in photography and optics as it affects the perspective, depth of field, and composition of an image. It also determines the magnification and clarity of the subject being captured.

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