Physics · 3.2.4 Thin converging lens · Image formation
Lens Imaging. Draw it.
Drag the object between O, F, 2F and beyond to see how the image changes. The three principal rays are drawn live so you can read off real/virtual, upright/inverted, and magnified/diminished. Each region corresponds to a real-world device.
0625 Topic 3.2.4 — Thin lens
Ray diagrams
Applications: camera · projector · magnifier · telescope · eye
Variables
1.50 f
10.0
2.0
Image properties
Object distance u
15.0 cm
Image distance v
30.0 cm
Magnification m
−2.00
Image height
4.0 cm
Image is
real
Orientation
inverted
Size
magnified
Sign convention
real-positive
Real-world application
📷 Camera / eye
When u > 2F, the image is real, inverted and diminished — exactly what a camera or human eye does.
📐 The five image-formation cases
Slide the object back and forth and watch the image jump between these regions:
- u > 2F — image is real, inverted, diminished, between F and 2F. Camera, eye, photography.
- u = 2F — image is real, inverted, same size, at 2F. Photocopier (1:1).
- F < u < 2F — image is real, inverted, magnified, beyond 2F. Projector, microscope objective.
- u = F — image is at infinity. Rays emerge parallel. Spotlight, search beam.
- u < F — image is virtual, upright, magnified, on the same side as the object. Magnifying glass, eyepiece, simple microscope.
📋 The three principal rays
- A ray parallel to the principal axis refracts through the focal point F on the opposite side.
- A ray through the optical centre C passes straight through with no deviation.
- A ray through the focal point F on the object side emerges parallel to the principal axis.
The image forms where any two of these rays meet (for real images), or where their backward extensions meet (for virtual images).
🎯 Syllabus reference (0625)
- 3.2.4 Thin converging lens — describe the action of a thin converging lens on a beam of light; define principal focus and focal length; draw and use ray diagrams for an object placed at various distances from a converging lens.
- Describe the characteristics of a real image and contrast them with those of a virtual image.
- Describe the use of a single lens as a magnifying glass.
- State that the human eye uses a converging lens to focus light onto the retina; identify short sight and long sight.