Lenses

1. Lenses

2. Lenses in General • Lenses work by refraction • 2 refractions, one when light enters lens and one when it leaves lens. • Light is bent due to it having a lesser speed in the glass or plastic • Lens shapes • Fattest in the middle is converging lens • Thinnest in middle is diverging lens

3. Image Terminology • Real images form from converging light rays and can be projected while virtual images form from diverging rays and cannot be projected • Magnified images are larger than the object, reduced are smaller. • Erect images are right-side-up while inverse images are upside-down.

4. Lens Terminology • Focal point: where rays parallel to the principal axis would meet after passing through converging lens • Focal Length: Distance between focal point and center of lens • False focal points: points on principal axis of diverging lens where rays appear to come together.

5. Ray Tracing • Process allows quick determination of what type of image forms. • Diverging lens always gives same image (Reduced, Erect and Virtual) • Converging Lens has 1 of 3 images depending on object distance. • Use principal rays to determine type of image • Use 1/f= 1/p + 1/q and M=-q/p to find location and magnification. Also cc/2 = f • Positive side of lens is opposite object

6. Lens Aberrations (Flaws) • Spherical Aberration occurs when rays from different parts of the lens focus to different focal points • Can be limited by reducing amount of lens used • Front surface mirror avoids the problem • Chromatic aberration occurs when different colors of rays focus to different focal points. • Achromatic lens can eliminate this.