How this calculator works
A thin converging lens forms a real image when the phone lies outside its focal point. The lens equation connects the two distances measured from the lens principal plane. Magnification scales every screen dimension, including its diagonal, if aspect ratio is preserved. A simple magnifier has aberrations; focus, screen brightness and usable image size must be checked experimentally.
Formula
1/f = 1/u + 1/v; magnification magnitude M = v/u; image diagonal = M times screen diagonal.
Worked example
With f = 0.1 m and u = 0.11 m, v = 1.1 m and magnification is 10. A 6 inch screen becomes a 60 inch diagonal image in the ideal model.
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Frequently asked questions
Why is the image inverted?
A single converging lens reverses a real image about the optical axis.
What if the phone is inside the focal length?
The lens forms a virtual image that cannot be caught on the wall.
Does a bigger image stay equally bright?
No. Spreading the available light over a larger area reduces illuminance.