A pinhole camera is used to produce an image of a bird that is 3.8 m away. If the size of the bird's image on the screen is 3.0% of the size of the bird, what is the distance from pinhole to screen?
A) 5.7 cm
B) 23 cm
C) 11 cm
D) impossible to determine given the information.

Question

Quizplus · Accepted Answer

We can use the thin lens equation: 1/f = 1/di + 1/do, where f is the focal length (which is very small for a pinhole camera), di is the distance from pinhole to image, and do is the distance from pinhole to object. Since the image is inverted, we use the negative value of di. Let's call the distance from pinhole to screen "x". Then we have:

1/f = -1/di + 1/do
1/f = -1/(0.03*3.8) + 1/x
Assuming f is small enough to be negligible compared to the distances involved, we can simplify:

1/x ≈ 1/(0.03*3.8)
x ≈ 11 cm

A Pinhole Camera Is Used to Produce an Image of a Bird