Question

2. The actual light sensor size of a digital camera is 14.9 mm x 22.3 mm. You want to take a photo of your little sister, who is 1.25 m tall. Your camera has a 35 mm focal length lens. How far from the camera should your sister stand in order to produce a 22 mm tall image on the light sensor?

Answer 1

2)

Given,

The focal length, f = 35 mm = 0.035 m

We know,

The magnification, M = d₂ / d₁

where,

d₁ is the object to lens distance
d₂ is the image to lens distance

By the lens equation, 1/f = (1/d₂) + (1/d₁)

1/d₂ = 1/f - 1/d₁

d₁ = 1 / [M(1/f - 1/d₁)]

d₁/f - 1 = 1 /M

d₁ = f (1/M + 1)

Where, M = 0.022 / 1.25 = 0.0176

So, d₁ = 0.035 [ (1/0.0176) + 1]

d₁ = 2.024 m