IGCSEPhysicsCambridge (CIE)Revision Notes3. WavesLightReal Images

Real Images (Cambridge (CIE) IGCSE Physics): Revision Note

Exam code: 0625 & 0972

Written by: Katie M

Reviewed by: Tim

Updated on 24 August 2026

Converging lens - real image

Constructing converging ray diagrams

The three main rules for constructing ray diagrams are as follows:

Rays passing through the principal axis will pass through the optical centre of the lens undeviated
Rays that are parallel to the principal axis will be refracted and pass through the focal point f
$Diagram of a converging lens showing an incident ray parallel to the horizontal principal axis refracted through the focal point on the far side.$
Rays passing through the focal point f will emerge parallel to the principal axis

Drawing converging ray diagrams of real images

Object placed beyond 2f

Ray diagram of a converging lens forming a smaller, inverted real image when the object is placed beyond twice the focal length on the principal axis.

When an object is placed beyond 2f (to the left of the lens), the image that forms (to the right of the lens) will have the following properties:

The image forms...	between f and 2f
The nature of the image is...	real
The orientation of the image is...	inverted
The size of the image is...	diminished

Object placed at 2f

Ray diagram of a converging lens showing an object at 2f forming an inverted real image at 2f on the opposite side, with principal focus points marked.

When an object is placed at 2f (to the left of the lens), the image that forms (to the right of the lens) will have the following properties:

The image forms...	at 2f
The nature of the image is...	real
The orientation of the image is...	inverted
The size of the image is...	the same

Object placed between f and 2f

Ray diagram of a converging lens with object between f and 2f, showing rays forming a real, inverted, magnified image beyond 2f on the other side.

When an object is placed between f and 2f (to the left of the lens), the image that forms (to the right of the lens) will have the following properties:

The image forms...	beyond 2f
The nature of the image is...	real
The orientation of the image is...	inverted
The size of the image is...	magnified

Worked Example

Draw a ray diagram to show how a converging lens can be used to form a diminished image of a real object.

Label the object, image and principal foci of the lens on your diagram.

Answer:

Step 1: Start by drawing and labelling a principal axis and the lens as a line or a very thin ellipse

Diagram of a converging lens shown by a vertical double arrow crossing a horizontal line labelled principal axis.

Step 2: Mark and label the focal points on each side of the lens

Diagram of a converging lens shown by a vertical double arrow crossing a horizontal line labelled principal axis and focal points F marked symmetrically on either side of the lens.

Step 3: Draw and label the object at a distance greater than the focal length on the left side of the lens

Tip: For a diminished image, the object should be placed a distance of at least 2f away from the lens

Step 4: Draw a ray through the optical centre of the lens

Step 5: Draw a second ray from the object to the lens which is parallel to the principal axis

Step 6: Draw the continuation of the ray passing through the focal point on the right side of the lens

$Diagram of a converging lens shown by a vertical double arrow crossing a horizontal line labelled principal axis and focal points F marked symmetrically on either side of the lens. An upright object is placed at a distance at least 2F away from the centre of the lens. A ray is drawn from the top of the object towards the optical centre of the lens. A ray parallel to the principal axis is drawn towards the lens. The parallel ray is refracted and passes through the focal point on the far side.$

Step 7: Draw and label the image at the point where the rays meet

Step 8: Check your final image and make sure everything is included to gain the marks

For a three-mark question, examiners will be looking for:
- One ray drawn through the optical centre of the lens
- A second ray drawn which produces a diminished (smaller) image (which must pass through a labelled focal point)
- Both the object and the image must be drawn and labelled correctly

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