Thin Lenses
Ray Diagrams for Converging Lenses
These diagrams show refraction occouring only once in the middle of the lens. This is for ease of sketching. Refraction occours at both boundries.
Rule 1
Rays that are parallel to the principal axis will refract through the principal focul point, F.
Rule 2
Rays passing through the secondary focul point, F', will refract parallel to the principal axis.
Rule 3
Rays that are headed towards the center of the lense will pass through with very little deflection. This rule is an approximation and not totally accurate. The refracted ray is parallel to the incident ray, but the refracted ray is shifted slightly.
Converging Lenses Examples
The above rules can be applied to find where the image of an object appears.
When an object is placed at a point greater than 2F', the image is dimished, real, and inverted.
When an object is placed at 2F', the image is the same size, real, and inverted.
When an object is placed at a point between 2F' and F', the image is enlarged, real, and inverted.
When an object is placed at F', there is no image because the rays do not converge.
When an object is placed inside F', the image is enlarged, virtual, and upright.
