Lenses work by refracting light rays using the principle of refraction. There are two main types of lenses: convex and concave. A convex lens is thicker in the middle and converges light rays, forming a real, inverted, and reduced image. A concave lens is thicker on the edges and diverges light rays, forming a virtual, upright, and reduced image. Ray diagrams can be used to determine the location, orientation, size, and type of image formed by a lens by tracing the path of three key rays: the parallel, focal, and vertex rays.

1. LENSES

2. What are lenses?
Lenses came from the Latin word for “lentil”, a type of bean
used in cooking

3. How do lenses work?
•Refraction is the bending of light as it
passes from one transparent substance into
another.
Refracted rays
light rays

5. Types of lenses
Concave Lens
Convex Lens
* It is thicker at the center than the edges
* It forms real images and virtual images
depending on the position of the object.
• It is thicker at the edges and
thinner at the center
• It forms upright, reduced
image and virtual image

6. Types of lenses
Convex Lens
A convex lens is also called
converging lens because it
makes parallel light rays
passing through it bend
inward and converge at a
spot just beyond the lens
know as focal point (F)

7. Types of lenses
Concave Lens
A concave lens is
sometimes called
diverging lens because
it makes parallel light
rays curve outward or
diverge

8. Ray Diagramming for Lenses

9. V
F F
2F 2F
Imaginary line that will serve as
guide when to bend the
refracted ray in graphical
method
• Vertex (V) – the geometric center of a lens
• Focal /Focus (F)- The point where light rays converge or appear to converge when parallel rays pass
through a lens
• Focal length- the distance from the vertex to the focal point
note: twice the focal length you have 2f , which will help you in describing the image FORM BY A LENS
f f

11. In Front and Back Side of a Lens

12. Three Most useful Rays for ray Diagramming
for Lenses
Where:
P- Parallel ray
F- Focal Point/Focus
V- Vertex
P-F Ray
F-P Ray
V- Ray
At least two of these rays can be used to describe the
images formed by a lens

13. Three Most useful Rays in Lenses
Convex Lens Concave Lens
A ray of light parallel to the
principal axis is refracted passing
though the principal focus, F
located behind the lens
A ray of light parallel to the principal
axis is refracted passing though the
principal focus, F located in front of
the lens
V F
F
P-F Ray
V F
F
P–F Ray

14. Three Most useful Rays in Lenses
Convex Lens Concave Lens
A ray of light passing through the
focus, F in front of the lens is
refracted parallel to the principal
axis.
A ray of light directed towards the
focus, F behind the lens is refracted
parallel to the principal axis.
V F
F
F-P Ray
V F
F
F- P Ray
Imaginary extension
of the refracted ray

15. Three Most useful Rays in Lenses
Convex Lens Concave Lens
A ray of light passing through the vertex, V of a the lens and continue to
travel in the same direction.
V F
F
V-Ray
V F
F

17. Describing the Characteristics of the
images formed by lenses
Location of the Image
Between F and 2F
Behind the lens
Between V and F
At F
Beyond F and farther than 2F
At 2F
In front of the lens
(if the image is virtual)
Orientation of the
Image
Upright or Inverted

18. Describing the Characteristics of the
images formed by lenses
Size of the Image Same, Reduced, Enlarged
Type of the Image Real Image or Virtual
Image

19. Difference between REAL OR VIRTUAL
REAL IMAGE VIRTUAL IMAGE
Inverted image
Positive (+) value of the distance of image (d )
Negative (-) value of the height of image (-h1)
(means inverted, therefore real image)
Negative (-) value of the magnification (-M)
(means real image)
Formed in front of a lens and CAN BE
projected on a screen
Upright image
Negative (-) value of the distance of image (-d)
Positive (+) value of the height of image (h)
(means upright, therefore virtual image)
Positive (+) value of magnification (M)
(means virtual image)
Formed in front of a lens and CANNOT be
projected on a screen

20. Sample Ray Diagramming of Convex
Lens
Note: the image will be drawn inverted if the refracted rays merge or
converge in the lower or below the principal axis
1.Using a ruler and a pencil, draw the principal axis on a piece of
paper.
2.Draw the lens and then a vertical line that crosses lens.
3.Mark two important points in the principal axis, the Vertex, Focal
Point/Focus, and the 2F (twice the value of focal length).
4.Draw the object in front of the lens based on the given location.
5.From the tip of the object, draw at least two of these rays : P-F Ray,
F-P ray, or V ray
6.From the point where the actual refracted rays merged to the
principal axis, draw the inverted image of the object.

22. Sample Ray Diagramming of Convex Lens
Describe the Characteristics of the Image Formed
Location of the Image
Orientation of the Image
Size of the Image
Type of Image
Behind the lens (between F and 2F)
Inverted
reduced
Real Image

23. Sample Ray Diagramming of Concave
Lens
1.Using a ruler and a pencil, draw the principal axis on a piece of
paper.
2.Draw the lens and then a vertical line that crosses lens.
3.Mark two important points in the principal axis, the Vertex, Focal
Point/Focus, and the 2F (twice the value of focal length).
4.Draw the object in front of the lens based on the given location.
5.From the tip of the object, draw at least two of these rays : P-F Ray,
F-P ray, or V ray
6.From the point where the virtual refracted rays merged to the
principal axis, draw the upright image of the object.
Note: the image will be drawn upright if the virtual refracted rays
merge or converge in the upper or above the principal axis

25. Sample Ray Diagramming of Convex Lens
Describe the Characteristics of the Image Formed
Location of the Image
Orientation of the Image
Size of the Image
Type of Image
In front the lens (same side where the
object is located)
Upright
Reduced
Virtual Image