## What sees better: Your eye or a phone camera?

Do you know how close together can words be on a road sign so you can still read it from a distance? How close can objects can be to be seen as separate objects? Is the vision of person with spectacles better than yours? Why we can see much smaller objects using scanning electron microscopy comparing to white light microscopy?

### Materials

Red and blue dots pattern
Mobile phone camera
Meter   stick

### Directions

Prepare and print the pattern of red dots and blue dots,
1 mm across, spaced 1 mm apart. Tape the pattern on a wall. Than stand far enough away from the patterns in a well-lighted room so that they appear to be solid lines. Take a picture of a pattern on your mobile camera. Walk slowly toward the patterns and carefully observe the patterns taking a camera picture every few steps. At some point can you see separate dots instead of solid lines? Which dots can you see first, red or blue? Record the distance where you can see the separate blue dots and the distance where you can see the separate red dots. Can you see dots faster than your camera can do?

### Explanation

The resolution (Rayleigh’s criterion) is defined as the shortest distance between two points on a specimen that can still be distinguished by the detector, such as: the human eye, mobile phone camera, microscope, as separate entities. The resolution is limited by the diffraction. When light reflected from two very small objects passes through a small circle aperture (like the pupil of your eye or camera) it generates diffraction pattern seen as a two bright spots (called the Airy disks) surrounded by dimmer rings of light around the disk. Rayleigh’s Criterion states that you will be able to tell that there are two small dots rather than one dot when the center of one diffraction disk falls on the edge of the other. The diameter of this pattern is related to the wavelength of the illuminating light and the size of the circular aperture. Shorter wavelengths are capable of resolving details to a greater degree than are the longer wavelengths. For example: the resolution of the light microscope in which the wavelength is 400 nm is ~ 200 nm. The resolution of the scanning electron microscope in which the wavelength of an electron is about 0.017 nm, is ~ 1nm. It means that we can use a white light microscope to see a structure of hair (hair thickness ~100,000 nm), but to see viruses we have to use scanning electron microscope (virus size ~100 nm).