When to use this calculator
Find ideal image distance for a thin lens and a real object. Uses the thin-lens sign convention: converging f positive, diverging f negative, virtual image distance negative.
Explore the optics & quantum relationships calculators for other questions in this topic. For a related calculation, use the Young Double Slit Fringe Calculator: Estimate ideal double-slit fringe spacing on a distant screen.
PUTTING IT INTO PRACTICE
Thin Lens Image Distance: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Focal length (cm) | 10 |
| Object distance (cm) | 30 |
| Result | 15 cm |
- Check the input labels and enter the example values above.
- Apply the relationship: Image distance = 1/(1/focal length − 1/object distance).
- The result is 15 cm, rounded for display.
How to interpret your result
Uses the thin-lens sign convention: converging f positive, diverging f negative, virtual image distance negative.
Use the stated sign convention for lenses and angles measured to the normal for refraction. Vacuum wavelength differs from wavelength inside a material. These models do not account for every optical aberration or material response.
Frequently asked questions
Why can a refracted-angle calculation have no real result?
When Snell’s-law sine exceeds one, the ideal ray model predicts total internal reflection rather than a real transmitted angle.
When is the thin lens image distance calculator useful?
Find ideal image distance for a thin lens and a real object. Uses the thin-lens sign convention: converging f positive, diverging f negative, virtual image distance negative.
How do I use the thin lens image distance calculator?
Enter focal length (cm), object distance (cm). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Image distance = 1/(1/focal length − 1/object distance).
What should I check before using the result?
Uses the thin-lens sign convention: converging f positive, diverging f negative, virtual image distance negative.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
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