Convex Lenses

Convex lenses are also called converging lenses.

• Object is symbolized by the upward arrow
• Real focus is on the side opposite the object
• Virtual focus is on the same side as object
• 2f is the same as R for a mirror
• f is still the focus as with a mirror
• O is the optical center
• Convex lens creates same images as a concave mirror (sometimes, real, virtual, or nonexistent)
• Example is a magnifying glass

Image Formation

• When object is beyond 2f, image is real, inverted, smaller than object
• When object is at 2f, image is real, inverted, same size as object
• When object is at f, image is nonexistent
• When object is between f and the lens, image is larger, virtual, and upright

Comparison to Concave Mirror

• Concave mirrors (also converging ) yield the same image results as convex lenses.
• The same sign rules hold for the lenses that apply to mirrors.
• Also called “diverging“
• The only image formed is smaller, virtual, and upright

Concave Lenses

• These cave-in in the middle and are comparable in image formation to convex mirrors
• Use the same sign rules and equations as mirrors!

 

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