Physics

Smartphone Projector Calculator

Find the magnification of a DIY lens projector.

Lens focal length

Phone-to-lens distance

Calculated Output

Magnification (×) 2

Lens-to-screen distance 300

Formula: 1/f = 1/d_o + 1/d_i; M = d_i ÷ d_o

Step-by-Step Breakdown

1. Values used:

2. Lens focal length = 100

3. Phone-to-lens distance = 150

5. Magnification = 2×

6. Lens-to-screen distance = 300

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The math behind it

The thin-lens equation 1/f = 1/d_o + 1/d_i gives the image distance; magnification M = d_i ÷ d_o.

100 mm lens, phone at 150 mm → image at 300 mm, 2× magnification.

Why is the image upside down?

A single converging lens flips the image, so you mirror the phone display.