Machine Vision Optics Troubleshooting

POMEAS optical applications team · Reviewed by Tiger Xie · Published 2026-10-16

Troubleshooting starts from the symptom and works back to the cause. Each guide below takes an image defect, names the optical causes that produce it, and gives an order in which to eliminate them, so that a repair is confirmed rather than guessed.

These guides assume the setup was correct at commissioning. If the system has just been installed, check the setup and calibration material in the technical guides index first.

1. The guides in this index

A. Blur, shift and shading

• Why a Lens Turns Blurry After Adding a Prism: 4 Causes — Adding a prism can defocus a machine vision lens.
• Why Does a Zoom Lens Shift After Changing Magnification? Causes & Solutions — Why the image shifts after you change zoom magnification: the causes in continuous and motorized zoom lenses, how to tell them apart, and how to fix each one.
• Industrial Lens Vignetting: 3 Causes and Fixes — Three root causes of dark corners in telecentric, zoom and FA lenses, a step-by-step diagnosis flow, and which fixes are worth the money.

B. Fault classes and isolation order

• Motorized Zoom Lens Troubleshooting: 4 Fault Classes — Four fault classes behind nearly all POMEAS motorized zoom lens field issues, plus the wiring rules that prevent most of them - and the one action that damages motors.

2. How to use this index

Start with the symptom the image shows, not with the component you suspect. Each guide gives an elimination order, and following it is faster than testing the most likely cause first, because different optical faults often share a symptom.

3. Frequently asked questions

Why did focus change after adding a prism or fold mirror?

Adding an element to the optical path changes the path length and, depending on the element, introduces aberration or tilt. Work through path length and back focus first, then mechanical tilt, then the quality of the element itself.

Why does the image move when magnification changes?

Magnification change alters the optical path through the lens group, so a lens that is not properly centred and parfocal shifts the image as it zooms. This is a setup condition rather than a defect; the centring and parfocality procedure is the fix, and if the condition will not hold, the cause is mechanical.

Why are the corners darker than the centre?

Corner shading usually means the image circle is being exceeded somewhere in the chain, at a magnification setting or aperture where the lens no longer covers the sensor. Check the lens image circle against the sensor diagonal at every magnification you use, then check for mechanical obstruction in the path.

How do I tell whether the fault is optical or mechanical?

Test at a fixed magnification with the optics untouched. If a defect appears while nothing optical changes, the cause is mechanical, electrical or thermal. If it appears only when magnification or focus is adjusted, it is optical or electromechanical and belongs with the lens control chain.

Is there a standard order for eliminating optical faults?

One that saves time: confirm the symptom reproduces at a defined magnification, check illumination before the lens, check the mechanical path before the electronics, and change one element at a time.

What should I log so a fault can be diagnosed later?

The magnification and focus command values, illumination setting, exposure time and the image itself. Most optical faults are differences between two states, so a saved reference image with its settings is what makes the next occurrence diagnosable in minutes.

4. Related POMEAS resources

• Machine Vision Optics Selection Guides: Complete Index
• Machine Vision Inspection Application Cases: Complete Index
• Machine Vision Optics Technical Guides: Complete Index
• Machine Vision Optics Calculators and Formulas: Complete Index
• Machine Vision Optics Comparisons: Complete Index
• All POMEAS machine vision knowledge articles
• POMEAS zoom lenses
• POMEAS telecentric lenses
• POMEAS FA lenses
• POMEAS machine vision lighting
• POMEAS Technical Reference Series — full-length notes on optical imaging performance testing and measurement method

Talk to a POMEAS Engineer About an Imaging Fault

If an image defect has appeared, send the image together with the magnification, focus and illumination settings that produced it, and a saved reference image if you have one. Diagnosis is faster when two states can be compared.

Email: [email protected] | WhatsApp: +86 185 9810 2007

Reviewed by Tiger Xie.