1. Lenses

2. What are lenses?
Lens – a thin, transparent piece of glass or plastic that has at least one curved side
The sides may be concave, convex, or plane
Lenses that make parallel light rays come together (converge) are called converging lenses
Lenses that make parallel light rays move apart (diverge) are called diverging lenses

3. Lenses
Lenses that make parallel light rays come together (converge) are called converging lenses
Lenses that make parallel light rays move apart (diverge) are called diverging lenses

4. Images Formed By A Converging Lens
Three rays may be used when locating an image in a converging (convex) lens:
Ray is parallel to the PA from object and is refracted through the focal point on the far side of the lens
Ray passes directly through the centre of the lens
Ray passes through the focal point on the same side of the lens and refracts parallel to PA

5. Images Formed By A Converging Lens
S – smaller
A – inverted
L – between F and 2F
T - real

6. Converging Lenses Can Produce Different Types of Lenses
Images formed by a converging lens will differ depending on whether the object is at one of 5 possible locations:
Beyond 2F
At 2F
Between 2F and F
At F
Inside F

7. Object at 2F F 2F F
S – same
A – inverted
L – at 2F
T - real

8. Object Between F and 2F F 2F F S – larger A – inverted L – past 2F
T - real

9. Object at F F 2F F
NO CLEAR IMAGE

10. Object Within F F 2F F S – larger A – upright L – other side of object
T - virtual

11. Image Characteristics of a Converging Lens
Object
Image
Location
Size
Attitude
Type
Beyond 2F
At 2F
Between
2F and F
At F
Inside F
between 2F and F
real
smaller
inverted
same
inverted
at 2F
real
larger
inverted
beyond 2F
real
No clear image
larger
upright
behind object
virtual
Optics Bench

12. Optical Devices – uses of Lenses
Where must the lens be placed?
A copy camera produces an image that is real and the same size
A hand magnifier produces an image that is virtual and larger
A slide projector produces an image that is real and larger
A 35-mm camera produces an image that is real and smaller
A spotlight produces parallel light: there is no image
A photographic enlarger produces an image that is real and larger
2F from the object
Inside F
Between F and 2F
Beyond 2F
At F
Between F and 2F