Background

Visual angles are the angles of objects relative to an individual’s eyes. That is, if we drew lines from the top and bottom of an object and extended those lines to your eyes, we would have the visual angle of that object. This angle represents the size of the image tha the object has on the retina. The larger the angle the larger the retinal image.

To make this point more concrete, think of throwing a ball to a friend several yards away. When the ball ball leaves your hand, its retinal image is a certain size defined by the angle the size of the obect has at your eye. As the ball moves away from you, the retinal image size of the ball shrinks as the distance increases.

Use this activity to see how retinal image size depends upon the distance and the size of the object.

Instructions

Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

Illustration Tab

Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Red Arrow Position: moves the red arrow closer or farther from the eye.
The two arrows are matched: Selecting Physically makes the two arrows have the same physical size. Selecting Retinal Image Size adjusts the size of the red arrow so that it will always have the same retinal image size as the blue (fixed) arrow.
Show Data: when checked, summary data such as the arrow eight, distance from the eye, and the angleb (retinal image size) are presented.

Reset

Pressing this button restores the settings to their default values.