# Using the eye

Use the eye to look at any object marker, or any real or virtual image produced from it.

Three blue lines appear when you first place the eye on-screen:

- The centre line is the line of sight and must pass through the object/image being viewed. The eye will try to focus on the first object/image encountered or the image produced by a mirror or lens. With no objects/images present, the eye focuses to its maximum focal length.
- The outer two lines define the region of interest. Narrowing this region narrows the angle from which the eye accepts light. If the region is larger than the object/image being viewed, the object/image will appear small on the display screen.

The display screen (picture) shows the image/object that the eye is attempting to focus on. It shows perspective, intensity and blurring.

## See also:

- Eye