FA Lens Focal Length & Working Distance Calculator
Estimate the focal length required to cover a target field of view at a given object distance, then compare it with POMEAS FA lenses in the datasheet database.
Calculator
Formula and applicable conditions
| Required magnification | β = sensor width / FOV width |
|---|---|
| Focal length (paraxial) | f = β × u / (1 + β) = sensor width × u / (FOV width + sensor width)u is the object distance from the principal plane. Working distance is measured from the lens front, so the two are not identical. |
| Field of view at a given distance | FOV = sensor width × (u − f) / f |
Parameter definitions
| Effective sensor size | Imaging area in mm from the camera datasheet. |
|---|---|
| Target field of view | Object area to be covered. |
| Object distance | Distance used by the thin-lens model. Start with the mechanical working distance and correct it for the lens construction. |
Worked example
- 1/1.8-inch camera (7.18 × 5.32 mm), FOV 50 mm, object distance 300 mm.
- f = 7.18 × 300 / (50 + 7.18) = 37.7 mm, so a 35 mm FA lens is the nearest standard option.
- At 300 mm the 35 mm lens gives FOV = 7.18 × (300 − 35) / 35 = 54.4 mm, slightly wider than requested.
Frequently asked questions
Why is working distance not the same as object distance?
Working distance is measured from the lens front (or a defined mechanical reference), while the thin-lens model uses the distance from the principal plane. For long distances the difference is small; for short distances and high magnification it matters and must be corrected with real lens data.
Is the estimated focal length exact?
No. It is a paraxial thin-lens estimate. Real lenses are thick-lens systems with a defined flange focal distance and focus range. Use the estimate for shortlisting and confirm the real field of view by test.
What if the required focal length is between two models?
Choose the nearest available focal length and check the achievable field of view at your working distance with this calculator, then confirm by sample test. A slight change of working distance often covers the gap.
Does the tool consider distortion?
The focal length estimate does not. Distortion values from the datasheet are shown for candidate models because distortion affects measurement accuracy, especially for metrology tasks.
Request a POMEAS lens recommendation
Submit the parameters and the calculation result below. The form posts to the existing POMEAS contact interface; nothing is sent automatically and no data is shared with third parties.