Line Scan Camera Lens for High-Speed Sorting Systems: How to Select FOV, Resolution and Working Distance for Conveyor-Based Optical Sorting

High-speed sorting systems have a demanding optical requirement: every object crossing a conveyor, belt, feeder or multi-lane transport path must be imaged with enough detail for the sorting system to make a reliable decision while production continues at speed. In these machines, the line scan camera lens is responsible for mapping a potentially wide sorting zone onto a long linear sensor while preserving the detail needed to differentiate acceptable products, reject objects, dimensional variations, surface abnormalities, orientation differences or other visible classification features. Selecting the wrong field of view can reduce pixels available on each object, while an unsuitable working distance can create mechanical integration problems or unnecessary magnification loss. For OEMs, the correct lens therefore has to balance sorting width, object size, smallest classification feature, sensor resolution, working distance and full-field image quality rather than being selected by focal length alone.

This blog focuses specifically on line scan camera lens selection for conveyor-based high-speed optical sorting, which is different from conventional frame-based sorting optics and from sorting systems dedicated to one particular product category. Line scan imaging is particularly useful when objects move predictably through an inspection line because successive scan lines can reconstruct the moving inspection area continuously. Kyptec Automation® already identifies conveyor-based inspection, high-speed industrial imaging and sorting-related applications within its broader machine-vision guidance, while its dedicated Line Scan Camera Lens collection currently contains three focal-length choices: 25 mm, 35 mm and 50 mm. These optics are specified for 4K 7 μm and 8K 3.5 μm line-scan configurations and are designed for continuous high-resolution imaging where consistent sharpness and low distortion are important.

Why Line Scan Optics Are Well Suited to High-Speed Conveyor Sorting

A conveyor sorting machine may continuously present objects across a belt that is hundreds of millimetres or more in width. Unlike a stationary inspection station where every product is stopped at the same position, the sorting system must image objects while they are moving, often with several objects or lanes entering the inspection zone simultaneously. A line scan system builds the image from successive lines as the belt moves, making it particularly useful where the conveyor provides the mechanical motion required for image reconstruction.

For the lens, the central challenge is cross-belt coverage. The optical field must include every valid object position while preserving enough resolution for the smallest feature that controls the sorting decision. If the belt width is unnecessarily over-framed, each product receives fewer pixels. If the field is too narrow, legitimate objects near the belt edge may leave the usable inspection zone. The ideal line scan lens therefore provides sufficient margin for real product movement without wasting large portions of the linear sensor on unused conveyor background.

Start With Sorting Width, Not Focal Length

One of the most common errors when specifying an industrial sorting camera lens is starting with a preferred focal length. OEMs should first establish the required physical field of view.

For a conveyor sorter, this usually includes the active conveyor width plus the maximum lateral product movement that is considered valid. If a belt is 800 mm wide but products only occupy a controlled 700 mm inspection region, the optical design does not necessarily need a dramatically larger field. Conversely, if products can legitimately travel close to the belt edges, sufficient margin must be included.

Once this physical FOV is known, focal length and working distance can be evaluated together to produce that field on the selected line sensor.

This approach prevents the machine from being designed around the lens when the lens should instead be selected around the machine.

Calculate Pixels per Millimetre Before Selecting the Lens

The most useful first-resolution calculation is:

Pixels per millimetre = Number of active line pixels ÷ Object FOV in millimetres

For example, an 8,192-pixel line covering an 800 mm sorting width provides approximately 10.24 pixels/mm. If the same camera is configured to cover 1,200 mm, sampling falls to approximately 6.83 pixels/mm.

This matters because a sorting system does not classify the belt itself; it classifies features on the objects.

Suppose a product is 20 mm wide but the feature distinguishing a reject from an acceptable product is only 0.5 mm. At 10.24 pixels/mm, that feature spans about five pixels. At 6.83 pixels/mm, it spans about 3.4 pixels. The reduced sampling may materially change classification reliability even though the complete product remains clearly visible.

The correct optical specification should therefore be based on the smallest classification feature, not merely the minimum object size.

Pixels per Object Is an Important Sorting Metric

Sorting OEMs often discuss camera resolution in terms of 4K or 8K, but object-side resolution provides a more meaningful engineering measure.

A 25 mm object imaged at 8 pixels/mm receives roughly 200 pixels across its width. A 5 mm object at the same scale receives only about 40 pixels.

If classification depends only on overall size, this may be sufficient. If the system needs to identify a small notch, crack, surface mark, damaged corner or orientation feature, the critical feature may receive far fewer pixels.

This is why two optical sorting systems using identical 8K cameras can have very different real inspection capability: the physical FOV determines how those pixels are distributed over the conveyor.

Wide Conveyor FOV Versus Small Feature Detection

Wide sorting machines create a fundamental optical trade-off. The OEM wants one camera to cover as much conveyor width as possible, but every additional millimetre of FOV spreads the available sensor pixels over a larger physical region.

The solution is not automatically to use the widest possible lens. Instead, calculate the required pixels/mm first and determine the largest FOV that still satisfies the classification requirement.

If one camera cannot cover the entire belt while preserving sufficient object detail, the optical design requirement itself indicates that the inspection architecture may need to be divided. The line scan camera lens should not be forced to solve an impossible relationship between enormous FOV and extremely small features.

Kyptec Automation® KL-1402 for Compact Wide-Coverage Sorting Machines

The Kyptec Automation® KL-1402 25 MM Line Scan Camera Lens provides the shortest focal length in the current Kyptec Automation® line scan range. Its live specification lists 25 mm focal length, F2.8–22 aperture, M42 mounting and support for 4K 7 μm and 8K 3.5 μm line-scan systems.

This geometry can be evaluated where a sorting-machine OEM has limited camera height but still needs comparatively broad conveyor coverage. Examples include compact multi-lane sorting machines, industrial parts sorters and conveyor inspection stations where mechanical space above the transport surface is restricted.

Because wider coverage reduces object-side sampling, the final decision should always confirm that the smallest sorting feature remains sufficiently resolved at the intended belt width.

Working Distance Is a Mechanical and Optical Parameter

Working distance is often treated as a secondary lens specification, but in sorting equipment it should be established early because the physical camera position may be constrained by conveyor guards, feeding mechanisms, rejection devices, overhead structures or service-access requirements.

The working distance, focal length and sensor geometry jointly determine the object field.

Moving the camera farther away generally increases the amount of conveyor covered while reducing object magnification. Moving it closer generally narrows FOV and increases available pixels/mm.

An OEM should therefore answer two questions simultaneously:

How wide must the sorting zone be?

How high above the conveyor can the camera realistically be mounted?

The best line scan camera lens is the focal length that satisfies both conditions while preserving the minimum required object-side resolution.

Product Height Variation Changes the Effective Geometry

Sorting systems rarely handle perfectly flat objects at one identical height. Items may differ in thickness or may not sit perfectly flat on the conveyor.

When product height changes, the distance between the object surface and lens changes. That can affect focus and slightly alter magnification.

A system designed only around the conveyor plane can therefore perform differently on taller products.

OEMs should specify the minimum and maximum expected inspection heights and test whether important classification features remain sufficiently sharp throughout that range. Where dimensional measurements form part of the sorting decision, changes in magnification should also be considered.

Do Not Use Depth of Field as a Substitute for Correct FOV Design

Depth of field can help accommodate reasonable object-height variation, but it does not solve insufficient object resolution.

Stopping the aperture down may keep differently sized objects within acceptable focus, but if the optical FOV is so wide that the smallest classification feature receives too few pixels, increased depth of field cannot recover that lost sampling.

FOV, resolution and depth tolerance should therefore be solved separately before being optimized together.

Kyptec Automation® KL-1404 for Medium Conveyor Geometry

The Kyptec Automation® KL-1404 35 MM Line Scan Camera Lens provides an intermediate 35 mm focal length with F2.8–16 aperture, M42 mounting and published compatibility with 4K 7 μm and 8K 3.5 μm line-scan cameras.

This focal-length class can be evaluated for medium-height conveyor sorting machines where the OEM wants a more controlled field than a compact wide-angle geometry while retaining a practical camera stand-off.

It can be relevant to multi-lane component sorting, packaging sortation and industrial grading machines where products occupy a significant conveyor width but fine classification details must still receive useful sensor sampling.

Smallest Object Size Is Not Always the Smallest Required Feature

A sorting specification that says “minimum product size = 10 mm” is incomplete.

The vision system may need to distinguish that product from another 10 mm product based on a 1 mm corner, a 0.4 mm opening, a small edge break or another visible detail.

The lens should therefore be selected using the smallest decision-making feature, not the smallest object.

This distinction is important for buyer-intent lens selection because an OEM can otherwise purchase a camera-lens combination that images every product clearly but still lacks enough detail to classify them reliably.

Full-Field Sharpness Matters in Multi-Lane Sorting

A multi-lane sorting system may place products near the centre and near both ends of a long sensor.

If fine-detail performance deteriorates significantly near the field edges, classification accuracy can become lane dependent.

The OEM should test the same reference object or defect at left, centre and right positions. If the sorting feature is visible only in the centre, the optical system is not truly qualified for the full sorting width.

Kyptec Automation® describes its dedicated line scan camera lenses as engineered for consistent sharpness across the full field and minimal distortion in high-speed continuous imaging. These are especially useful characteristics to evaluate when multiple sorting lanes share one linear sensor.

Distortion Matters When Sorting Uses Size or Position

Some sorters classify only from colour or visible surface condition, while others also use width, position, edge location or dimensional thresholds.

When image geometry contributes to the sorting decision, low distortion becomes more important because image position should correspond predictably to object position.

This is also relevant when the rejection mechanism depends on a calculated lateral coordinate. If a product is detected at a particular position across the belt, the reconstructed image should represent that location consistently.

The Kyptec Automation® line scan range is positioned for precision defect detection and measurement with minimal distortion, supporting this type of geometry-sensitive application.

Conveyor Speed Does Not Change Cross-Belt FOV, but It Changes Image Quality Requirements

The lens determines cross-line imaging geometry, but conveyor speed affects how quickly successive image lines must be captured.

At higher transport speeds, the available exposure may become shorter. This can reduce optical signal and make subtle classification features harder to preserve.

For that reason, the correct line scan lens should not be qualified only on stationary products. Actual sorting samples should be imaged at the intended operating speed.

The smallest classification feature should remain visible under final production exposure, aperture and conveyor-speed conditions.

Aperture Selection for High-Speed Optical Sorting

A larger aperture can help collect more light when exposure time becomes short. However, opening the lens fully is not automatically the best solution because products with different heights may require more focus tolerance.

A smaller aperture can increase usable depth of field, but excessive stopping down eventually reduces fine-detail performance and also decreases the light reaching the sensor.

The correct aperture is therefore the setting that maintains the smallest sorting feature across the required object-height range while providing enough signal at production speed.

Kyptec Automation® KL-1406 for Sorting Systems With Greater Camera Stand-Off

The Kyptec Automation® KL-1406 50 MM Line Scan Camera Lens is the longest focal-length option currently listed in the Kyptec Automation® line scan collection. The live collection confirms 50 mm alongside the 25 mm and 35 mm options.

This geometry can be evaluated for sorting machines where a greater camera stand-off is mechanically desirable or where the required conveyor field is better matched to longer focal-length optics.

Such configurations can be useful in larger industrial sorting frames where cameras must be mounted above surrounding machine structures while still preserving a controlled inspection zone.

4K Versus 8K for Conveyor-Based Sorting

The 4K versus 8K decision should be made from sorting width and minimum feature size.

If a 4K sensor provides sufficient pixels/mm for every valid product and classification feature, increasing sensor resolution is not automatically necessary. An 8K system becomes more useful when the OEM wants to cover a wider conveyor while maintaining similar object sampling, or needs to resolve smaller features across the same FOV.

Kyptec Automation® publishes its current line scan optics for both 4K 7 μm and 8K 3.5 μm configurations, enabling OEMs to evaluate the same focal-length family across different resolution requirements.

Practical Example: Wide-Belt Multi-Lane Sorting Machine

Consider an 8K sorting machine covering a 1,000 mm conveyor. With 8,192 pixels across the field, the nominal sampling is approximately 8.19 pixels/mm.

A 30 mm object receives roughly 246 pixels across its width. If the smallest classification feature is 0.5 mm, it occupies approximately four pixels.

If the OEM widens the FOV to 1,500 mm without changing the sensor, sampling falls to about 5.46 pixels/mm and that same 0.5 mm feature receives fewer than three pixels.

This calculation should be performed before the mechanical camera position and lens are frozen because it determines whether a single wide-field optical configuration can satisfy the required sorting accuracy.

Practical Example: Mixed-Height Object Sorting

A conveyor handles products with different thicknesses. The sorting feature is visible on the upper surface, so taller objects are closer to the camera than shorter objects.

The OEM should test the smallest critical feature at both height extremes. If the feature becomes soft on one group, aperture, working distance or camera geometry may need refinement.

Simply selecting a higher-resolution sensor does not remove the focus problem.

Practical Example: Multi-Lane Component Sorter

A machine uses several lanes across one conveyor and relies on small edge features to classify products.

The same known reference component should be placed in the centre lane and both outer lanes. If classification confidence falls toward the edges, full-field optical performance, alignment and focus should be investigated before algorithm thresholds are altered.

A Kyptec Automation® line scan camera lens provides a focused optical platform for this architecture because the current product family is designed specifically for high-resolution continuous imaging across long line-scan sensors.

Frequently Asked Questions About Line Scan Camera Lenses for High-Speed Sorting Systems

1. How do I choose a line scan camera lens for an optical sorting machine?

Begin with conveyor width, active sorting width, smallest classification feature, camera sensor pixel count, pixel pitch, product-height range and available working distance. Calculate pixels/mm before choosing focal length, then select the optical geometry that covers the required sorting region without sacrificing the resolution needed for classification.

2. How wide should the field of view be for a conveyor sorting system?

The FOV should cover the full valid sorting region plus realistic lateral product movement. Excessive additional background should be avoided because every unnecessary millimetre of FOV reduces object-side pixels per millimetre.

3. How do I calculate sorting-system resolution?

Divide active line pixels by the physical conveyor FOV in millimetres. Then multiply the resulting pixels/mm by the size of the smallest classification feature. This tells the OEM approximately how many native sensor pixels represent the feature used for the sorting decision.

4. Should I calculate pixels per object or pixels per defect?

Both are useful, but pixels on the smallest decision-making feature are more important. A product can occupy hundreds of pixels while the tiny feature that differentiates it from another sorting class occupies only a few.

5. Can one line scan camera inspect multiple sorting lanes?

Yes, provided all lanes fit within the qualified FOV and the smallest relevant feature in the outer lanes still receives sufficient optical resolution. Full-field sharpness should be verified rather than assumed from centre performance.

6. What happens if I use too wide an FOV in an optical sorter?

The number of pixels representing each millimetre decreases. Large objects may still appear clear, but fine sorting features can become poorly sampled and classification reliability can decline.

7. Does working distance affect optical sorting accuracy?

Yes. Working distance influences FOV, magnification and pixels/mm. It can also affect whether the camera fits mechanically above the conveyor. The final lens should therefore be selected together with the available camera mounting height.

8. How does product-height variation affect a sorting lens?

Different product heights change object distance, which can affect focus and magnification. OEMs should qualify the smallest sorting feature on both the shortest and tallest expected products rather than testing only the conveyor surface.

9. Is an 8K line scan camera always better than 4K for sorting?

No. An 8K configuration offers greater cross-line sampling, but it is valuable only when the wider or finer-resolution requirement needs those additional pixels. A correctly designed 4K system may already satisfy many sorting applications.

10. What Kyptec Automation® line scan camera lens can be evaluated for compact wide-belt sorting machines?

Kyptec Automation® KL-1402 25 MM is the shortest current focal-length option and is specified with F2.8–22 aperture, M42 mounting and support for 4K 7 μm / 8K 3.5 μm systems. It can be evaluated where broad conveyor coverage is required from comparatively limited stand-off.

11. When is Kyptec Automation® KL-1404 useful for sorting machines?

Kyptec Automation® KL-1404 35 MM provides an intermediate focal-length geometry with F2.8–16 aperture and M42 mounting. It can be evaluated where the machine requires a balanced relationship between conveyor coverage, stand-off and object magnification.

12. When should Kyptec Automation® KL-1406 be considered for conveyor sorting?

Kyptec Automation® KL-1406 50 MM can be considered where greater camera stand-off is available or preferred and the required sorting FOV matches longer focal-length geometry. It is the longest focal-length option currently listed in the Kyptec Automation® line scan collection.

13. Does conveyor speed affect which line scan lens I should buy?

It affects the operating optical requirements because higher speed can require shorter exposure. The chosen lens and aperture should preserve enough image signal and fine-detail contrast for the smallest sorting feature under actual production-speed conditions.

14. Can line scan lenses be used when products appear randomly across the conveyor width?

Yes, provided the entire valid product region is inside the optical FOV and sufficient image quality is maintained across that complete width. Random lateral position makes edge-to-edge lens performance especially important.

15. Why does my sorting system work well in the centre but make more mistakes near the conveyor edges?

Possible causes include edge sharpness, camera alignment, illumination variation, focus or insufficient optical coverage. Testing one reference product at multiple positions is a useful way to determine whether the problem follows image location rather than product type.

16. Can one sorting lens handle different product sizes?

Potentially yes, if the largest objects fit inside the valid field and the smallest important feature on the smallest product remains adequately sampled. The product-height range should also remain inside the usable focus tolerance.

17. Should an optical sorting lens be tested using real production products?

Yes. Resolution charts are useful for initial optical evaluation, but real products reveal the actual contrast, edge characteristics and subtle visual features the sorter must classify. Final qualification should include representative good and reject samples at production speed.

18. What information should an OEM provide before buying a line scan camera lens for a high-speed sorting machine?

Provide active sorting width, conveyor width, active line pixels, pixel pitch, physical sensor length, smallest and largest object dimensions, smallest classification feature, number of sorting lanes, maximum product height, available working distance and conveyor speed. These parameters allow the Kyptec Automation® Line Scan Camera Lens collection to be evaluated from actual sorting geometry rather than focal length alone. The live collection currently contains dedicated 25 mm, 35 mm and 50 mm options, and OEMs planning volume integration can also use the Kyptec Automation® OEM Orders page.

Conclusion

Selecting a line scan camera lens for a high-speed sorting system starts with understanding what the machine actually needs to classify. Conveyor width determines the required field of view, but the smallest decision-making feature determines whether that FOV provides enough usable resolution. For this reason, OEMs should calculate pixels per millimetre and pixels on the smallest feature before deciding whether a 4K or 8K system and a particular focal length can satisfy the sorting requirement.

Working distance should then be matched to the mechanical machine layout. Product-height variation, full-field sharpness, aperture and production speed should be qualified using real sorting samples rather than relying solely on static resolution charts. A system that covers the complete belt but cannot resolve the feature controlling rejection is under-resolved, while a system that provides excessive magnification but cannot cover legitimate product positions is equally unsuitable.

The Kyptec Automation® Line Scan Camera Lens portfolio provides a focused family of Kyptec Automation® KL-1402 25 MM, Kyptec Automation® KL-1404 35 MM and Kyptec Automation® KL-1406 50 MM line scan camera lens options. The current live product pages specify 4K 7 μm / 8K 3.5 μm support, M42 mounting and adjustable aperture, while Kyptec Automation® describes the series as engineered for high-precision continuous imaging with uniform illumination, minimal distortion and consistent full-field sharpness.

For high-speed optical sorting machines, wide-belt sorting systems, multi-lane component sorters, conveyor classification machines and industrial grading equipment, Kyptec Automation® line scan camera lenses provide a strong dedicated optical foundation for designing around the three parameters that matter most to the OEM: correct FOV, sufficient object-side resolution and a mechanically practical working distance.