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Physics
Converging Lens
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Move the object, change the focal length and the object height to see how the image through a converging lens changes in position, orientation, size and nature (real or virtual).
Converging lens simulation area
Real image · inverted · smaller than the object
Object beyond 2F
Real image – inverted – smaller than the object.
- d′
- 15 cm · behind the lens
- k
- −0.5 · inverted
- |h′|
- 2.5 cm · object h = 5 cm
Substitution: 1/10 = 1/30 + 1/15
Convention: d′ > 0 for a real image, d′ < 0 for a virtual image.
Why?
When d > 2f, the real image lies between F′ and 2F′, inverted and smaller than the object. The farther the object moves away, the closer the image moves to F′ and the smaller it gets; moving the object toward 2F makes the image grow.
- An image equal to the object There is a unique position for an image exactly equal to the object.Not completed
- A virtual, upright, larger image Try moving the object very close to the lens.Not completed
- An image very far from the lens From outside, bring the object close to F and watch d′.Not completed
Model notes
- The lens is thin and ideal: thickness and aberrations are ignored; for ray construction the lens is treated as large enough for every special ray to pass through it.
- Light travels from left to right; the object AB is real and perpendicular to the optical axis, with A on the axis.
- The image follows 1/f = 1/d + 1/d′ and k = −d′/d with this sign convention: d > 0; d′ > 0 for a real image (behind the lens) and d′ < 0 for a virtual image (on the object side). Example: f = 10 cm and d = 5 cm give 1/10 = 1/5 + 1/d′, so d′ = −10 cm, a virtual image 10 cm from the lens.
- For readability the vertical axis is drawn magnified relative to the horizontal axis (usually about 2–3 times, depending on the frame size), and the frame picks its scale so the object and 2F′ stay in view. This magnification does not change the image position or where the rays meet.
- Image screen: light from each object point passes through the lens (aperture D = 6 cm) and converges at the image point. A screen at a distance s from the lens cuts this cone into a light spot of diameter D·|s − d′|/d′, centered on the ray through the optical center; the wider the spot, the dimmer it is. The image counts as sharp when |s − d′| ≤ 0.75 cm. This is an approximate geometric model that ignores diffraction and aberrations.
- Zooming, panning or "Fit to view" only change the view, not any physical quantity.