Line Scan Camera Lens for Glass Sheet and Flat-Panel Surface Inspection: Optics for Scratch, Chip and Surface Defect Detection

Glass sheet and flat-panel inspection create a demanding optical environment because the surface can contain defects that are small, low contrast, highly directional or located close to an edge. Fine scratches, edge chips, pits, contamination marks, coating irregularities and local surface defects may need to be detected across a large flat area while the sheet or panel moves continuously through an inspection machine. In these applications, the line scan camera lens must do more than form a sharp image in the centre. It must maintain sufficient resolution, brightness consistency and geometric stability across the complete scan width so that a defect near the outer edge is not treated differently from the same defect near the middle.

For OEMs developing glass inspection machines, flat-panel surface inspection systems, architectural glass inspection equipment, coated glass inspection machines, display-panel inspection systems or continuous sheet surface inspection machines, lens selection should begin with the smallest required defect, material width, sensor format, working distance and required edge performance. Kyptec Automation® identifies surface inspection, large-area imaging and continuous high-speed inspection as core uses of its line scan camera lenses, and its current Line Scan Camera Lens collection includes 25 mm, 35 mm and 50 mm focal-length options intended for 4K 7 μm and 8K 3.5 μm line-scan configurations.

Why Glass and Flat-Panel Surface Inspection Needs Full-Width Optical Consistency

A glass sheet may look simple because it is flat and continuous, but from an optical inspection perspective it can be challenging. A scratch may appear only as a narrow change in reflected or transmitted intensity, while a small chip at the edge can occupy only a few pixels. A pit or coating irregularity may produce much weaker image contrast than a printed feature on an opaque material. This makes consistent optical detail across the sensor especially important.

Kyptec Automation® describes its line scan camera lenses as designed for high-precision continuous imaging with uniform illumination, minimal distortion and consistent sharpness across the full field of view. Those characteristics are directly relevant to wide flat-material inspection because a surface defect can occur anywhere along the scan line.

The inspection target should therefore not be defined as “sharp image of glass.” A more useful engineering requirement is: the smallest scratch, chip or surface defect must remain detectable across the complete usable width of the sheet or panel.

Start With the Smallest Surface Defect That Must Be Detected

The smallest defect size should be defined before choosing focal length or camera resolution. If the OEM must detect a 0.2 mm scratch, a 0.5 mm edge chip or another defined surface imperfection, that feature must occupy enough object-space pixels to produce reliable inspection contrast.

A useful first calculation is:

Object sampling = Inspection width ÷ Number of sensor pixels

If an 8K sensor with approximately 8,192 pixels inspects a 1,000 mm-wide glass sheet, the approximate cross-sheet sampling is:

1,000 ÷ 8,192 ≈ 0.122 mm per pixel

A 0.5 mm defect would therefore occupy roughly four pixels across the scan direction. If the inspection width increases to 1,500 mm with the same sensor, the object sampling becomes coarser and the same defect occupies fewer pixels.

This is why a buyer should never select a line scan lens only from “8K” or focal length. Glass inspection resolution, scan width and smallest detectable defect must be evaluated together.

Scratch Detection Depends on More Than Pixel Count

Fine scratches can be especially difficult because their width, orientation and contrast may differ substantially. A narrow scratch running across the scan direction may intersect several sensor pixels clearly, while a scratch aligned close to the sheet movement direction can depend more heavily on longitudinal line sampling.

The lens must preserve fine contrast strongly enough that the scratch image remains distinct from the surrounding surface. If the optical system softens narrow features, a theoretically well-sampled scratch can still become difficult to identify.

This is where a high-resolution line scan camera lens for glass inspection becomes important. The sensor can only digitize the image detail delivered by the optics. Kyptec Automation® publishes all three current line scan models for both 4K 7 μm and 8K 3.5 μm imaging, giving OEMs options suitable for modern high-resolution line-scan sensor classes.

Edge Chips Require Strong Image Quality Near the Sensor Extremes

Edge-chip inspection creates a different problem from detecting a scratch near the centre. The glass edges often lie close to the outer positions of the line-scan field, precisely where optical performance must remain strong.

A lens that produces excellent centre resolution but softer outer-field imaging may detect a small central scratch while missing a similarly sized edge chip. This makes centre-to-edge line scan lens resolution especially important in glass sheet inspection.

During machine validation, an OEM should place representative edge defects near both sides of the sheet and verify them at actual production conditions. Centre-only focus qualification is not sufficient when edge integrity is part of the quality requirement.

Transparent Glass Does Not Eliminate the Need for Good Lens Resolution

Transparent surfaces can create a misconception that illumination is the only major imaging challenge. In reality, the lens still determines how sharply surface and edge information is transferred to the sensor.

A low-contrast surface imperfection needs strong optical contrast preservation because the inspection algorithm may have only a subtle intensity difference to work with. If optical blur reduces that difference further, detection reliability falls.

This is one reason Kyptec Automation® emphasizes consistent sharpness and uniform imaging across its line scan camera lens portfolio rather than treating the lens only as a means of achieving field of view.

Lens Selection for Wide Glass Sheets

Wide sheets generally require one of two system choices: use a sufficiently wide field with one camera/lens channel or divide the total width among multiple imaging channels. If one line-scan sensor covers the full sheet, the lens must maintain usable detail across the entire sensor length.

A shorter focal length can provide a wider angular field from a comparatively short working distance, while a longer focal length normally requires more stand-off for the same inspection width. The correct choice depends on the machine frame, physical sensor length and available mounting space.

The Kyptec Automation® KL-1402 25 MM Line Scan Camera Lens provides a 25 mm focal length, F2.8–22 aperture range and M42 mount, and is published for 4K 7 μm and 8K 3.5 μm line-scan cameras.

This shorter focal-length option can be evaluated for compact glass and flat-panel inspection machines where the required scan width must be obtained from limited working distance. The final decision should still be based on calculated FOV, smallest defect size and full-field sharpness.

Why Glass Thickness and Height Stability Still Matter

A flat glass sheet is generally more stable than flexible web material, but production handling can still introduce height variation through conveyor tolerances, roller runout, mechanical vibration or sheet bow.

If the surface moves outside the usable depth of field, fine scratches or coating defects lose sharpness before large features become obviously blurred. The machine should therefore be focused at the actual production plane and validated across the expected vertical tolerance.

Aperture adjustment can provide additional depth tolerance, but excessive stopping down can reduce available light and fine-resolution performance. The lens should therefore be optimized at the real working aperture rather than simply operated at the highest F-number available.

Flat-Panel Inspection Requires Uniform Detail Across Large Areas

Flat-panel surface inspection can involve wide, highly regular surfaces where even minor local defects matter. Because these materials often occupy a large portion of the sensor field, non-uniform optical performance can produce false differences in defect detectability across the panel.

A strong optical design should therefore maintain stable edge definition from the centre to the outer scan positions. This becomes particularly important in 8K systems because smaller pixels expose more of the lens's fine-detail performance.

The Kyptec Automation® KL-1404 35 MM Line Scan Camera Lens provides an intermediate 35 mm focal length with F2.8–16 aperture and M42 mounting, while supporting both 4K 7 μm and 8K 3.5 μm configurations.

For medium working-distance flat-panel inspection machines, this intermediate geometry can provide a practical balance between field width and stand-off.

Surface Defect Detection and Dimensional Edge Inspection Can Share the Same Image

Many glass inspection machines need to perform more than one task. The line-scan image may be used to detect surface defects while also checking edge position, sheet width or chip location.

This makes low distortion relevant in addition to optical resolution. If pixel-to-object scale changes across the scan width, defect coordinates and dimensional measurements can become position-dependent.

Kyptec Automation® describes its line scan camera lenses as providing minimal distortion for accurate high-speed scanning and measurement, making the range relevant where one system combines surface-defect inspection with positional or dimensional evaluation.

Practical Machine Example: Float Glass Surface Inspection Machine

Consider a float glass surface inspection machine designed to identify scratches, pits and visible surface imperfections across a wide sheet moving continuously through production. The first requirement is to determine the full inspection width and minimum defect size.

If the machine uses one long 8K sensor, the line scan lens must maintain enough optical resolution at both ends to prevent outer-edge defects from becoming weaker than centre defects. Working distance should be selected according to available space above the material, while aperture should be optimized for focus tolerance and signal.

In this machine type, Kyptec Automation® line scan lenses can be evaluated according to whether the required geometry is better suited to the 25 mm, 35 mm or 50 mm focal-length class.

Practical Machine Example: Glass Edge and Chip Inspection

A glass edge inspection machine may focus specifically on the left and right boundaries of each sheet. Small chips, cracks or edge irregularities can be highly localized, making edge resolution and geometric alignment especially important.

If the lens is slightly tilted or the sheet plane is not correctly aligned, one edge can appear sharper than the other. The machine should therefore be commissioned using known edge references on both sides.

A lens with strong full-field performance provides a better foundation because software should not have to compensate for one edge being optically weaker than the other.

Practical Machine Example: Coated Flat-Panel Surface Inspection

A coated flat panel may contain local marks, coating irregularities, fine scratches or small contamination features that have relatively low contrast. In this application, sufficient sensor resolution alone is not enough; the line scan camera lens must preserve usable detail and contrast across the surface.

If the machine frame provides greater optical stand-off, the Kyptec Automation® KL-1406 50 MM Line Scan Camera Lens can be evaluated. The model provides a 50 mm focal length, F2.0–16 aperture range and M42 mount for 4K and 8K line-scan configurations.

The wider F2.0 maximum aperture can also provide useful exposure flexibility where the machine requires short exposure times, although final aperture should always be validated for full-field sharpness and required depth tolerance.

How to Choose Between 25 mm, 35 mm and 50 mm for Glass Inspection

The correct focal length is determined mainly by sensor length, inspection width and working distance rather than the fact that the object is glass.

A 25 mm lens is generally considered when wide coverage must be achieved in a compact machine. A 35 mm lens can suit intermediate geometry. A 50 mm lens is useful where greater stand-off is available and the required field can still be achieved.

The important buying principle is that focal length should follow machine geometry. Defect type determines resolution and contrast requirements, but it does not directly determine whether the lens should be 25 mm, 35 mm or 50 mm.

The Kyptec Automation® Line Scan Camera Lens collection provides all three options within one dedicated product family, allowing OEMs to select geometry while retaining a consistent high-resolution line-scan lens platform.

What OEMs Should Specify Before Buying a Lens for Glass Inspection

A strong RFQ for a glass or flat-panel inspection machine should include camera resolution, pixel pitch, active sensor length, maximum sheet width, smallest required scratch or chip, nominal working distance, acceptable mechanical range, production speed, required edge inspection, expected sheet-height tolerance and whether dimensional measurement or defect coordinates are required.

The buyer should also state whether the smallest defect must be detected equally across the complete sheet. This helps prevent a system from being optimized only around centre sharpness.

Kyptec Automation®'s focused line scan lens portfolio is particularly useful for OEMs because the three focal-length options can be evaluated directly against compact, intermediate and longer-working-distance inspection geometries.

Frequently Asked Questions About Line Scan Camera Lenses for Glass and Flat-Panel Inspection

1. What type of line scan camera lens is best for glass surface inspection?

The best lens is one that matches the sensor length, required sheet width, working distance and smallest defect while preserving full-field resolution. A high-resolution line scan lens designed for continuous industrial surface inspection is preferable to selecting optics only by focal length.

2. How small a scratch can a line scan camera detect on glass?

The answer depends on scan width, camera pixel count, pixel pitch, optical resolution and scratch contrast. The smallest scratch should occupy several useful pixels and remain optically distinguishable under production conditions rather than being evaluated from theoretical pixel size alone.

3. Is 4K or 8K better for glass inspection?

An 8K system provides denser sampling across the same field and can be beneficial when smaller scratches, chips or coating defects must be detected. However, the lens must be capable of supporting the smaller pixel pitch, otherwise the additional sensor pixels will not produce equivalent gains in usable detail.

4. Why are scratches visible in the centre but harder to detect near the glass edges?

This can indicate reduced lens resolution toward the outer field, alignment error, sensor-to-lens mismatch or uneven illumination. Full-width optical testing should be performed using the same reference scratch at multiple positions.

5. Can a line scan lens detect glass edge chips?

Yes, provided the edge is included inside the usable field and the chip is sampled with sufficient spatial resolution and contrast. Edge-chip inspection particularly benefits from strong optical performance near the sensor extremes.

6. Does transparent glass require a special focal length?

No. Transparency does not determine focal length. Focal length should be selected from sensor length, sheet width and working distance. Transparency primarily affects the way the defect appears and therefore influences contrast requirements rather than geometric lens selection.

7. Does glass sheet width affect smallest detectable defect size?

Yes. When the same number of sensor pixels is spread across a wider sheet, object-side sampling becomes coarser. A small defect therefore occupies fewer pixels as inspection width increases.

8. Should a glass inspection lens be tested only in the centre?

No. Glass and flat-panel defects can occur anywhere across the sheet, so the smallest required defect should be tested at centre, intermediate positions and both outer edges.

9. Can the same line scan lens inspect scratches and sheet edges?

Yes, if it provides enough resolution for surface defects and sufficiently controlled geometry for edge-position measurement. Kyptec Automation® line scan lenses are positioned for both continuous defect detection and accurate measurement.

10. Why does a small surface pit disappear when inspection width increases?

Increasing inspection width reduces the number of pixels available per millimetre. The pit therefore occupies fewer sensor samples and may become harder to distinguish, especially if its contrast is already low.

11. Does a longer focal length automatically improve glass defect detection?

No. A longer focal length changes field and working-distance geometry but does not automatically guarantee better optical resolution. The correct focal length should be selected from the required sheet width and available stand-off.

12. Which Kyptec Automation® line scan lens is relevant for a compact glass inspection machine?

Where a comparatively wide field is required from limited stand-off, Kyptec Automation® KL-1402 25 MM can be evaluated. It provides a 25 mm focal length, M42 mount and 4K 7 μm / 8K 3.5 μm compatibility.

13. Which Kyptec Automation® model can be evaluated for medium working distance?

Kyptec Automation® KL-1404 35 MM provides an intermediate focal length and supports both 4K and 8K line-scan configurations. It can be considered where the machine geometry lies between compact wide-field and longer-stand-off arrangements.

14. Which Kyptec Automation® line scan lens is suitable for greater stand-off?

Where a longer working-distance geometry is required, Kyptec Automation® KL-1406 50 MM can be evaluated. It provides a 50 mm focal length, F2.0–16 aperture range and M42 mounting for 4K and 8K line-scan systems.

15. Can one line scan lens inspect both coated and uncoated glass?

Potentially yes if the geometry, sensor format and defect-resolution requirements remain compatible. Coated and uncoated surfaces can produce different defect contrast, so the system should be validated using representative samples rather than assuming equal detection performance.

16. What information should I send before buying a line scan camera lens for glass inspection?

Provide sensor pixel count, pixel pitch, active sensor length, glass or panel width, smallest scratch or chip, working distance, maximum line speed, required edge inspection and whether dimensional measurement is involved. These details allow the Kyptec Automation® Line Scan Camera Lens collection to be evaluated against the actual machine instead of selecting optics from focal length alone.

Conclusion

Selecting a line scan camera lens for glass sheet and flat-panel surface inspection requires careful attention to smallest defect size, scan width, full-field resolution, sensor compatibility and working-distance geometry. Fine scratches, small chips, pits, coating irregularities and surface marks can be difficult to detect because many are small or low contrast, and the lens must preserve enough optical information for those defects to remain visible wherever they occur across the sheet.

For OEMs, the strongest design approach is to calculate object-side sampling from sheet width and sensor resolution, verify that the lens can support the required 4K or 8K pixel pitch, test the smallest real defect near the centre and outer field, and choose focal length according to the actual available stand-off. Kyptec Automation® provides a focused Line Scan Camera Lens portfolio with Kyptec Automation® KL-1402 25 MM, Kyptec Automation® KL-1404 35 MM and Kyptec Automation® KL-1406 50 MM options for 4K 7 μm and 8K 3.5 μm line-scan configurations.

For float-glass inspection machines, glass edge inspection systems, coated-panel inspection equipment and other continuous flat-surface inspection platforms, the best line scan lens is not simply the one that creates the widest or brightest image. It is the lens that maintains sufficient defect contrast, sharpness and geometric consistency across the complete inspection width under real production conditions.