Here’s a little animation my daughter and I made to describe magnifying glasses.
Now here’s an easy experiment you can do with your kids. Hold something about a foot from your eyes. You should be able to easily focus on it. Now bring it slowly closer. At some point, you won’t be able to focus. Light bouncing off the object goes through the lens in your eye and gets projected on the retina (the back of the eye where all the detectors are located). The lens is designed to bring light from far away in focus right on the retina. As you bring something closer to your face, muscles in your eye stretch the lens to keep the object in focus.
Depending on your age and how near or far sighted you are, the distance where you can still focus will change. As you age, you lens in your eye becomes less able to change focus easily. If you are near sighted, your eye is stretched out and the lens can’t keep far away things in focus. Normally you wear extra lenses (eyeglasses or contacts) to compensate. If you take off your glasses, you can get something very close to your face and still focus. The opposite is true for far sighted people. They have to hold things farther away to see them in focus.
If you want to see an object close, you either need to be nearsighted and take off your glasses, or else you need an extra lens between you an the object. A magnifying glass held at just the right spot, can change where the light focuses, allowing you to see close objects clearly.
