Which Machine Vision Lens Do I Need? Calculate Focal Length from Field of View, Sensor Size and Working Distance

Choosing the right machine vision lens becomes much easier once three application parameters are known: the field of view you need to inspect, the actual camera sensor size, and the available working distance between the camera and the object. These three values determine the approximate focal length required for the imaging system and provide a practical starting point for selecting an industrial camera lens.

This calculation is useful whether you are designing a machine vision inspection system, automated quality control station, dimensional measurement system, barcode inspection system, robotic vision application, packaging inspection machine, electronics inspection system or another industrial imaging application.

A common mistake is to select an industrial camera lens only by looking at focal length, megapixel rating or sensor format. A 12 mm, 16 mm, 25 mm or 50 mm machine vision lens does not automatically provide a particular field of view. The actual image coverage depends on focal length together with sensor dimensions and working distance.

For engineers and buyers comparing machine vision lenses, the most useful approach is therefore to calculate the required focal length first and then check sensor compatibility, image resolution, mount, aperture, distortion, depth of field and optical resolution.

You can explore the complete Machine Vision Lens range from Kyptec Automation® while using the calculations in this guide to narrow the available choices. The collection includes lenses covering different focal lengths, sensor formats and resolution requirements.

What Does Focal Length Mean in Machine Vision?

Focal length is one of the main specifications that determines how wide or narrow an industrial camera sees at a given working distance.

A shorter focal length generally gives a wider field of view. An 8 mm or 12 mm lens, for example, normally covers a wider scene than a 25 mm or 50 mm lens when the camera sensor and working distance remain unchanged.

A longer focal length provides a narrower field of view and greater image magnification. This can be useful when the inspection target is relatively small or when the camera must be positioned farther away.

This is why searches such as “what focal length lens do I need,” “machine vision lens focal length calculator,” “industrial camera lens field of view calculator” and “how to select lens for machine vision camera” cannot be answered accurately from focal length alone.

The lens needs to be selected as part of the complete optical geometry.

What Is Field of View in Machine Vision?

Field of view, commonly abbreviated as FOV, is the physical area of the object or production line that must appear inside the camera image.

If a component is 80 mm wide but its entire outline must be inspected, designing the system for exactly 80 mm horizontal field of view gives almost no alignment tolerance. A practical system may instead require 90 mm, 100 mm or another suitable value so that the whole component remains visible despite normal positional variation.

Field of view can be expressed horizontally or vertically. You should perform the calculation using the sensor dimension corresponding to the field of view being considered.

For horizontal FOV, use active sensor width.

For vertical FOV, use active sensor height.

The calculation should normally be checked in both directions to confirm that the required inspection area fits completely inside the image.

What Is Working Distance?

Working distance is the approximate distance between the lens or camera imaging system and the object being inspected.

In a real industrial machine, working distance is often determined before the lens because mechanical constraints already exist. The camera may need to remain above a conveyor, outside a machine enclosure, behind protective glass or away from a moving component.

If you have more freedom to change camera position, working distance and focal length can be optimized together.

Increasing working distance while keeping focal length unchanged generally increases the field of view. Increasing focal length while keeping working distance unchanged generally reduces the field of view.

This relationship is one of the most important concepts when choosing a machine vision camera lens.

Why Sensor Size Matters When Selecting a Machine Vision Lens

Camera sensor size directly affects field of view.

A larger sensor captures a wider field of view than a smaller sensor when both cameras use the same focal length and working distance, assuming the lens provides sufficient image-circle coverage.

This is why simply asking for a “25 mm lens” is not enough when purchasing an industrial camera lens. The lens should be evaluated against the actual sensor dimensions of the camera.

Machine vision cameras are frequently described using optical-format labels such as 1/2 inch, 2/3 inch, 1 inch or 1.1 inch. These labels should not be inserted directly into a focal-length equation.

For the calculation, obtain the actual active sensor width and height in millimetres from the camera or image-sensor datasheet.

For example, a camera may be described as having a 2/3 inch sensor format, but the correct horizontal calculation requires the sensor's real active width in millimetres rather than converting 2/3 inch directly into millimetres.

This simple point prevents many lens-selection errors.

Machine Vision Lens Focal Length Formula

For an initial lens calculation, determine the sensor dimension, desired field of view and working distance using the same measurement units.

A useful geometrical relationship is:

Focal Length ≈ (Sensor Dimension × Working Distance) ÷ (Field of View + Sensor Dimension)

When working distance is much larger than focal length, engineers also frequently use the simplified approximation:

Focal Length ≈ (Sensor Dimension × Working Distance) ÷ Field of View

The simplified equation is convenient for initial estimates, while the first equation provides a more useful starting approximation when the object is relatively close to the lens.

These formulas should be treated as lens-selection estimates rather than guarantees of exact final field of view. Actual results can change because of lens design, principal-plane location, distortion, close-focus behaviour, sensor dimensions and manufacturing tolerances.

The final lens should therefore be verified with the actual camera, object and working distance whenever precise metrology or inspection coverage is required.

Worked Example 1: Calculate a Lens for a 100 mm Field of View

Suppose an inspection system requires a horizontal field of view of 100 mm. The active sensor width is 8.8 mm, and the available working distance is approximately 300 mm.

Using the more complete approximation:

Focal length ≈ (8.8 × 300) ÷ (100 + 8.8)

Focal length ≈ 2640 ÷ 108.8

Focal length ≈ 24.3 mm

A commercially available focal length close to this calculation is 25 mm.

If the camera and required optical resolution are compatible with a 2/3 inch format, a product such as the 25 mm Machine Vision Lens with 5 Megapixel and 2/3 inch format, Kyptec Automation® KL-1208 can therefore become a candidate for further evaluation. Kyptec Automation® KL-1208 is specified as a 25 mm C mount machine vision lens for a 2/3 inch image format and 5 megapixel applications. The important point is not to select it merely because it is 25 mm, but because the calculated focal length, sensor compatibility and required image resolution should all be considered together.

Worked Example 2: What Happens If Working Distance Changes?

Keep the same illustrative 8.8 mm sensor width and 100 mm field of view, but increase working distance from 300 mm to 600 mm.

The approximate focal length becomes:

Focal length ≈ (8.8 × 600) ÷ (100 + 8.8)

Focal length ≈ 48.5 mm

The required focal length has approximately doubled because the camera has moved much farther from the target while the required field of view remains unchanged.

This illustrates why buyers should always tell a machine vision lens supplier the working distance. Asking only for a lens that captures a 100 mm object is incomplete because a system operating at 200 mm working distance may require a substantially different focal length from a system operating at 600 mm.

For applications where the calculation points toward approximately 50 mm and a suitable 2/3 inch sensor is being used, the 50 mm Machine Vision Lens with 10 Megapixel and 2/3 inch format, Kyptec Automation® KL-1232 is one of the available options to evaluate. It is listed with a 50 mm focal length, C mount and 2/3 inch image format.

Worked Example 3: Selecting a Lens for a Wider Inspection Area

Consider a system where the active sensor width is approximately 8.8 mm, required horizontal FOV is 200 mm and working distance is 300 mm.

The approximate focal length is:

Focal length ≈ (8.8 × 300) ÷ (200 + 8.8)

Focal length ≈ 12.6 mm

This indicates that a lens around 12 mm may be worth evaluating.

The 12 mm Machine Vision Lens with 5 Megapixel and 2/3 inch format, Kyptec Automation® KL-1204 is one relevant option within the Kyptec Automation® range when the camera format and required resolution correspond to its specifications. Kyptec Automation® KL-1204 is specified as a 12 mm C mount lens for a 2/3 inch image format.

The example also demonstrates why wide field of view applications typically move toward shorter focal lengths.

Should I Choose the Exact Calculated Focal Length?

Not necessarily.

Suppose the calculation gives 23.7 mm. An industrial lens with exactly 23.7 mm focal length may not be available or necessary. A standard 25 mm lens could be evaluated instead.

Likewise, if the estimated focal length is 15.2 mm, a 16 mm machine vision lens may be a logical candidate.

After selecting the nearest practical focal length, the installer can often adjust camera working distance slightly to achieve the required field of view.

For example, the 16 mm Machine Vision Lens with 10 Megapixel and 2/3 inch format, Kyptec Automation® KL-1226 provides a 16 mm focal-length option for compatible 2/3 inch camera systems.

For a different camera format, lens selection must be checked again rather than assuming that the same model will be suitable.

Sensor Format Must Match the Lens Image Circle

Focal length calculation solves only one part of lens selection.

A lens must also produce an image circle large enough to cover the camera sensor. If the lens is designed for a smaller image format than the camera sensor, the corners of the image may become dark or unusable. This effect is commonly described as vignetting.

Using a lens designed for an image format equal to or larger than the camera sensor is generally the safer approach, provided the other optical specifications are suitable.

Kyptec Automation® provides machine vision lenses across multiple image formats, which makes it easier to select a focal length while also matching the camera sensor. For example, the 25 mm Machine Vision Lens with 10 Megapixel and 1 inch format, Kyptec Automation® KL-1216 is specified for a 1 inch image format, while Kyptec Automation® KL-1208 provides a 25 mm option designed for a 2/3 inch format. These lenses share a nominal focal length but are intended for different imaging requirements.

This is exactly why “25 mm machine vision lens” should never be the only purchasing specification.

Does Megapixel Rating Matter When Choosing an Industrial Camera Lens?

Yes.

The lens must preserve enough image detail for the camera sensor and inspection task.

A high-resolution camera does not automatically produce a high-resolution inspection image if the lens cannot resolve sufficient detail. The optical system should therefore be considered as a combination of lens quality, sensor pixel size, camera resolution, field of view, focus, lighting and image-processing requirements.

For basic presence detection, the optical-resolution requirement may be moderate. For fine defect detection, dimensional measurement, PCB inspection, semiconductor inspection or small-feature recognition, lens resolution becomes much more important.

This is why the Kyptec Automation® machine vision lens range includes different megapixel classes rather than treating focal length as the only specification. The selection should match both optical geometry and inspection detail.

Why Object Resolution Matters Before Buying a Lens

A useful buyer-intent question is not only “which focal length do I need?” but also “how small is the feature I need to detect?”

Suppose a camera captures 2448 horizontal pixels across a 100 mm field of view. The theoretical object-space sampling is approximately 100 ÷ 2448, or 0.0408 mm per pixel.

If the field of view is increased to 200 mm with the same camera, object-space sampling becomes approximately 0.0817 mm per pixel.

The wider view therefore captures less pixel detail per millimetre of the object.

This relationship explains why trying to inspect a very large area with one camera can reduce the ability to detect tiny defects. Sometimes the correct solution is not simply a wider lens. It may require a higher-resolution camera, a narrower field of view, multiple cameras or a different inspection geometry.

How Aperture and F Number Affect Machine Vision Lens Selection

The aperture controls the amount of light reaching the sensor and influences depth of field.

A wider aperture allows more light but generally provides shallower depth of field. A smaller aperture can increase depth of field, helping maintain focus when the inspected object varies in height, but it also reduces available light and can eventually introduce diffraction that reduces fine detail.

Industrial machine vision therefore requires a balance between aperture, lighting intensity, exposure time, object movement and desired depth of field.

The focal-length calculation tells you approximately which lens geometry you need. Aperture helps determine how that lens performs under actual imaging conditions.

What Is Depth of Field and Why Does It Matter?

Depth of field describes the range of object distances that appear acceptably sharp.

This becomes important when products do not remain at exactly the same distance from the camera. Packages on a conveyor may vary in height. Mechanical parts may have three-dimensional surfaces. Components inside bins may appear at different depths.

A machine vision lens that produces the correct field of view may still perform poorly if only a very thin section of the object remains in focus.

Depth of field is affected by focal length, aperture, working distance, acceptable blur and imaging magnification. This is why final lens selection should consider the physical application rather than relying exclusively on a focal-length calculator.

Lens Distortion Can Affect Measurement Accuracy

For simple presence or absence inspection, moderate distortion may be manageable. For dimensional measurement and precision metrology, it can become much more significant.

A conventional lens may show barrel or pincushion distortion, particularly toward the edge of the image. If dimensional measurements are made across the complete field of view, calibration or a lower-distortion optical solution may be required.

Machine vision buyers working on measurement systems should therefore evaluate distortion specification in addition to focal length, sensor size and resolution.

Kyptec Automation® positions its machine vision lens range for industrial inspection, measurement and automation applications, and individual product specifications and datasheets can be reviewed before final selection.

Lens Mount Compatibility Is Equally Important

The lens mount must physically and optically match the camera.

C mount lenses are widely used in industrial machine vision systems, but not every machine vision camera uses the same mount.

Before purchasing, confirm the camera mount type, flange requirements, available mechanical clearance and lens dimensions.

Several standard machine vision lenses from Kyptec Automation®, including Kyptec Automation® KL-1208, Kyptec Automation® KL-1216, Kyptec Automation® KL-1226 and Kyptec Automation® KL-1232, are listed with C mount interfaces.

A Better Way to Specify a Machine Vision Lens Before Purchase

Instead of requesting “a 25 mm industrial lens” or “a lens for a 5 MP camera,” define the complete application.

The most useful information is the camera sensor model or exact active sensor width and height, camera resolution, required horizontal and vertical field of view, working distance, smallest feature that must be detected, available illumination, object speed, acceptable distortion, required depth of field and lens mount.

With those values, lens selection becomes substantially more reliable.

Kyptec Automation® provides a broad industrial machine vision lens selection, which is useful because a buyer can evaluate multiple focal lengths and sensor formats within the same product family rather than attempting to adapt an unsuitable lens to the application.

For additional background, the existing industrial camera lens selection guide from Kyptec Automation® also explains important lens-selection parameters including focal length, sensor compatibility and working distance.

Frequently Asked Questions About Machine Vision Lens Selection

1. How do I calculate the focal length for a machine vision lens?

Start with the actual sensor dimension, required field of view and working distance. A useful approximation is focal length = sensor dimension × working distance ÷ (field of view + sensor dimension). Use sensor width with horizontal FOV and sensor height with vertical FOV. After calculating the result, choose the nearest practical machine vision lens focal length and verify the actual image. If your result is close to 25 mm, for example, you can compare suitable 25 mm options within the Kyptec Automation® machine vision lens range rather than choosing on focal length alone.

2. What focal length lens do I need for my industrial camera?

There is no single focal length that suits every industrial camera. The answer depends primarily on sensor size, desired FOV and working distance. Short focal lengths such as 8 mm or 12 mm are generally associated with wider viewing angles, while 35 mm, 50 mm and longer focal lengths generally provide narrower views at the same distance. The correct choice should be calculated for your exact camera and application.

3. How do I calculate machine vision field of view?

If focal length, sensor dimension and working distance are known, the relationship can be rearranged to estimate field of view. Because practical lenses depart from an ideal thin-lens model, use the result as an engineering estimate and validate it with the actual lens. For precise applications, always leave sufficient field-of-view margin rather than designing the object to touch the image boundary.

4. Is a 12 mm or 25 mm lens better for machine vision?

Neither is universally better. A 12 mm lens normally provides a wider field of view, while a 25 mm lens normally provides a narrower view with greater magnification at the same working distance and sensor size. Kyptec Automation® offers both focal-length ranges, including Kyptec Automation® KL-1204 at 12 mm and Kyptec Automation® KL-1208 at 25 mm for compatible 2/3 inch 5 MP applications. The better choice is whichever produces the required FOV and image detail for your inspection.

5. Does a larger camera sensor need a different lens?

Often, yes. A larger sensor changes the field of view produced by a given focal length and also requires a sufficiently large lens image circle. Lens sensor-format compatibility should therefore be checked whenever the camera changes. Kyptec Automation® provides lens options designed for different image formats, which helps buyers match optical coverage to the intended camera rather than selecting only by focal length.

6. Can I use a 2/3 inch lens on a 1 inch sensor?

It is generally not the preferred approach because a lens designed for the smaller image format may not fully cover the larger sensor, potentially causing vignetting or unusable image corners. A lens designed for the camera's sensor format or a larger compatible format is usually safer. For example, Kyptec Automation® KL-1216 is specifically listed as a 25 mm lens for a 1 inch image format, whereas Kyptec Automation® KL-1208 is a 25 mm lens for a 2/3 inch format.

7. Should I use sensor diagonal, width or height when calculating focal length?

Use the sensor dimension that corresponds to the required FOV. Use sensor width for horizontal field of view and sensor height for vertical field of view. Diagonal calculations can be useful for angle-of-view discussions, but machine vision installations are usually easier to design using horizontal and vertical dimensions independently.

8. Does working distance affect machine vision focal length?

Yes. Working distance strongly influences the required focal length. If the camera must move farther from the object while maintaining the same field of view, a longer focal length is generally required. If working distance decreases while FOV remains constant, a shorter focal length will normally be needed. This is why working distance should always be included when requesting an industrial camera lens quotation or recommendation.

9. Is a higher megapixel machine vision lens always better?

Not automatically. A lens should provide adequate optical performance for the sensor and inspection requirement. A higher-resolution lens can be useful with high-resolution cameras and small-feature inspection, but focal length, image format, distortion, aperture, working distance and lighting remain equally important. Choosing the highest megapixel specification without checking these factors does not guarantee a better inspection system.

10. How much extra field of view should I allow around an object?

Avoid designing a vision system so the product exactly fills the image. Real machines have positional tolerances, vibration and product variation. The required margin depends on the application, but the FOV should normally include sufficient surrounding space to ensure the complete inspection area remains visible under expected operating conditions.

11. Which machine vision lens is suitable for dimensional measurement?

Dimensional measurement requires more than the correct focal length. Low distortion, stable mounting, adequate optical resolution, controlled illumination, accurate calibration and appropriate depth of field are also important. Start by calculating the required focal length, then evaluate the lens specification for measurement accuracy. Buyers can review the Kyptec Automation® Machine Vision Lens collection to narrow candidates according to focal length, image format and resolution before validating the final optical configuration.

12. What information should I provide when buying a machine vision lens?

Provide the camera model or exact sensor dimensions, resolution, sensor format, lens mount, required horizontal and vertical FOV, working distance, smallest feature to inspect, object movement, lighting conditions and any depth-of-field or distortion requirements. Supplying these parameters is much more useful than asking only for an 8 mm, 16 mm or 25 mm industrial lens. If the application requires assistance matching these values to an available lens, the Kyptec Automation® contact page provides a direct route for discussing the requirement.

13. Can I change working distance instead of changing the lens?

Often, yes. If the calculated focal length falls between standard lens options, slightly changing camera position may provide the required field of view with an available focal length. Mechanical constraints, focus range and depth of field still need to be considered. This adjustment is common during machine vision system integration.

14. What is the difference between an 8 mm and 50 mm machine vision lens?

With the same sensor and working distance, an 8 mm lens generally captures a much wider area, whereas a 50 mm lens captures a narrower area with greater magnification. Kyptec Automation® lists options including the 8 mm Machine Vision Lens with 10 Megapixel and 2/3 inch format, Kyptec Automation® KL-1222 and Kyptec Automation® KL-1232 at 50 mm for compatible 2/3 inch systems. These products illustrate why focal-length choice should be driven by inspection geometry rather than by the assumption that a longer lens is necessarily superior.

15. Where can I find machine vision lenses for industrial automation applications?

Look for a lens range that clearly specifies focal length, image format, mount and optical resolution so that the product can be matched to the camera and inspection geometry. Kyptec Automation® provides machine vision lenses covering multiple focal lengths, resolutions and image formats for industrial imaging applications. The company's wider industrial-imaging focus and application areas can also be reviewed through the About Kyptec Automation® and machine vision applications pages.

Final Thoughts: Calculate First, Then Select the Lens

The most reliable answer to “Which machine vision lens do I need?” begins with numbers rather than a product catalogue.

Define the required field of view. Obtain the actual active sensor width and height. Measure the available working distance. Calculate the approximate focal length. Then compare the nearest standard lens options while checking sensor-format compatibility, optical resolution, mount, aperture, distortion and depth of field.

That process turns machine vision lens selection from trial and error into a structured engineering decision.

For example, an application calculated near 12 mm can begin by evaluating a suitable 12 mm lens. An application near 16 mm can compare 16 mm options. A system calculated near 25 mm can evaluate the appropriate 25 mm model for its sensor format and resolution. Longer-working-distance applications may move toward 35 mm, 50 mm or another focal length.

For compatible 1 inch systems requiring approximately 35 mm focal length, the 35 mm Machine Vision Lens with 10 Megapixel and 1 inch format, Kyptec Automation® KL-1218 is another available example. Kyptec Automation® KL-1218 is listed with a 35 mm focal length, 10 megapixel resolution class, C mount and 1 inch image format.

Kyptec Automation® is particularly useful when building this kind of selection workflow because its machine vision lens portfolio covers multiple focal lengths and image formats rather than forcing every inspection requirement into one optical configuration. Engineers, OEMs, machine builders and system integrators can therefore begin with the calculated optical requirement, compare compatible lenses and then validate the chosen configuration for the real inspection environment.

The objective is not to buy the shortest focal length, longest focal length or highest megapixel lens. The objective is to select the machine vision lens that gives the required field of view, sufficient image detail and stable optical performance at the actual working distance of the machine.

That is the foundation of a reliable industrial vision system.