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3. Lens Systems

Objects and Images for Lens Systems (Figure 3)

• Real objects have diverging rays and are on the same side as the incoming object rays.


• Virtual objects are not naturally occurring and have converging rays.


• Real images have a focal point that can be focused on a screen and therefore are on the same side as the outgoing image rays.

Click on image to enlarge.

Virtual images cannot be focused on a screen and are always on the left side of the lens system.

• A virtual object may also have a virtual image.


• When light rays are about to cross, they are considered to have positive (+) vergence (convergence) and when they are receding from their crossing point, they are said to have negative (-) vergence (divergence).


• Rays that cross at the focal point of the lens are considered to have an infinite amount of vergence. Therefore rays that are parallel (have no crossing point), has a vergence of zero.


• Converging lenses have real/inverted images that are on the opposite side of the lens from the object.


• Diverging lenses create virtual/erect images that are on the same side as the object.