# Question from simple lens diagram (camera)

by ZedCar
Tags: camera, diagram, lens, simple
 P: 332 1. The problem statement, all variables and given/known data A simple camera has a converging lens of focal length 50.0 mm. It is used to photograph a tree 3.00 m high. The tree is 8.00 m away from the lens. Calculate the distance v between the lens and the film, giving your answer in mm to three significant figures. 2. Relevant equations 1/f = 1/u + 1/v 3. The attempt at a solution 1/50 = 1/8000 + 1/(-v) v = -50.3 mm Is this correct? Thank you!
 P: 58 Why did you reason that the image distance was negative?
 P: 332 Hmmm, not sure why I done that actually... Have corrected to: 1/f = 1/u + 1/v 1/50 = 1/8000 + 1/v v = 50.3 mm
P: 58

## Question from simple lens diagram (camera)

That looks right. The negative image distance you got before implies that the film needed to be outside the camera to capture the image.
 P: 332 Thanks Squeezebox! When I want to calculate the linear magnification of the image, the following equation is used: m = v/u Do I use the same v and u values from above? (both in metres) i.e. 0.0503 / 8 = 0.0063
P: 58
 Quote by ZedCar Thanks Squeezebox! When I want to calculate the linear magnification of the image, the following equation is used: m = v/u Do I use the same v and u values from above? (both in metres) i.e. 0.0503 / 8 = 0.0063
Now you have the opposite problem. There's a negative sign in this one.

m= -v/u

The image gets flipped upside down. This happens with your eyes too; your brain flips the image back right side up.
 P: 332 Ah, so it'd be -0.0503 / 8 = -0.0063 So is the height of the tree, stated in the question as being 3.00 m, not required to obtain the linear magnification?

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