# Lenses: If given object height and focal length, is it possible to calculate

• Byrne
In summary, the problem is to calculate the diameter of the moon's image on a camera's film given the focal length of 35 mm and the radius of the moon as 1.74 x 106 m. However, it is not possible to solve the problem with only this information and the distance between the Earth and the moon must also be taken into account. The distance to the moon can be considered infinite for calculating the image distance from the lens, but not for calculating the image size on the film.
Byrne
the image's height? If so, how? I have the formulas, but see no way of making a substitution.

If you wanted to know the problem, it states:

The focal length of a camera is 35 mm and the radius of the moon is 1.74 x 106 m. Calculate the diameter of the moon's image that appears on the camera's film.

It's impossible to solve the problem using only the given information. However, if you look up the distance between the Earth and the moon from somewhere...

Byrne said:
the image's height? If so, how? I have the formulas, but see no way of making a substitution.

If you wanted to know the problem, it states:

The focal length of a camera is 35 mm and the radius of the moon is 1.74 x 106 m. Calculate the diameter of the moon's image that appears on the camera's film.

Take the moon's distance from the Earth to be infinite.

HallsofIvy said:
Take the moon's distance from the Earth to be infinite.
For the purpose of calculating the image distance from the lens, the distance to the moon can be considered infinite. But not for the purpose of calculating the image size on the film.

## 1. Can the distance between an object and a lens affect the focal length?

No, the distance between an object and a lens does not affect the focal length. The focal length is a fixed property of a lens and is determined by its physical characteristics.

## 2. How does the object height affect the focal length of a lens?

The object height does not directly affect the focal length of a lens. However, it can affect the size of the image formed by the lens.

## 3. Is it possible to use the focal length to determine the size of an object?

No, the focal length alone cannot be used to determine the size of an object. Other factors, such as the distance between the object and the lens, are also needed.

## 4. Can the focal length of a lens be changed?

Yes, the focal length of a lens can be changed by adjusting the distance between the lens and the object or by using additional lenses to modify the light rays passing through the lens.

## 5. How does the shape of a lens affect its focal length?

The shape of a lens can affect its focal length. Generally, a lens with a greater curvature will have a shorter focal length, while a flatter lens will have a longer focal length.

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