Optics in Machine Vision

Optics are a fundamental part of every machine vision system - and at the same time one of the most common causes of unstable inspection results. In many projects, lens selection is considered too late or treated as an isolated task, resulting in insufficient image quality, measurement errors or unnecessary design iterations.

The key point is that optics never operate in isolation. They must be precisely matched to the sensor, pixel size, working distance and lighting.

If you would like to understand the fundamentals of industrial machine vision, start with our introduction to What Is Machine Vision?

What sensor sizes are available - and why are they important?

Sensor size describes the physical area onto which the image is projected. In industrial machine vision, sensor sizes are typically specified in inches, such as 1/3", 1/2", 2/3" or 1".

Smaller sensors such as 1/3" and 1/2" are commonly used in compact and cost-sensitive applications. Larger sensors - such as 2/3" and 1" - are standard in many industrial inspection systems because they provide a wider field of view or higher image detail. Even larger sensor formats are used in high-resolution applications.

Sensor size directly affects the field of view. With the same lens, a larger sensor captures more of the object. At the same time, the lens must be compatible with the sensor size, as every lens is designed for a specific image circle. Exceeding this image circle results in vignetting or blurred image areas.

Sensor size is also closely related to camera technology. Differences in sensor architecture and pixel size are explained in more detail in Camera Technologies in Machine Vision.

Choosing the right camera is closely linked to sensor size. An overview of available camera models and sensor formats can be found in Industrial Cameras.

The most widely used standard in industrial machine vision is the C-mount, which offers broad compatibility and is typically used with sensors up to approximately 1".

The CS-mount is mechanically similar but has a shorter flange focal distance. CS-mount lenses cannot be mounted directly on C-mount cameras, whereas C-mount lenses can often be used on CS-mount cameras with an adapter.

For larger sensors or applications requiring higher optical performance, F-mount - systemsoriginally developed for photography - are frequently used. Additional mount types are available for specialised applications.

Standard lenses cover a broad range of applications and are widely used for general inspection tasks. They provide an excellent balance between performance and cost.

Macro lenses are designed for small fields of view and high magnification. They are ideal for inspecting small structures with high levels of detail.

Telecentric lenses are specifically designed for precision measurement applications. They minimise perspective errors and ensure that objects appear the same size regardless of height variations.

Typical applications are explained in Optical Metrology.

For precision measurement tasks, explore our range of Telecentric Lenses.

Wide-angle lenses provide a large field of view at short working distances but can introduce higher distortion and are therefore not suitable for every application.

How do pixel size and resolution affect lens selection?

The resolution of a machine vision system results from the interaction between the camera and the lens. Pixel size describes the physical dimensions of an individual sensor pixel.

Smaller pixels enable higher image detail but place greater demands on optical performance. If the lens cannot resolve sufficient detail, the camera's theoretical resolution cannot be fully utilised.

A practical rule of thumb is that a relevant feature should be represented by at least two to three pixels to enable reliable detection or measurement.

As a result, cameras and lenses should always be selected together. Treating them independently often leads to inefficient or unstable systems.

What role do aperture and depth of field play?

The aperture controls how much light reaches the sensor while also influencing depth of field.

A smaller aperture increases depth of field, allowing objects at different heights to remain in focus. However, it also reduces the amount of available light.

A wider aperture allows more light to reach the sensor but reduces depth of field. This can cause problems when objects are not precisely positioned or are moving.

In industrial applications, depth of field is often a critical factor in achieving stable and repeatable inspection results.

Why are working distance and mechanical design important?

Working distance describes the distance between the object and the lens. It influences the field of view, perspective and mechanical integration.

A longer working distance may simplify system integration but often requires higher-performance optics. Lens size and mechanical stability must also be considered, especially in industrial environments with vibration, temperature fluctuations or limited installation space.

Robust mechanical design is essential for repeatable inspection results.

What role do wavelength and lighting play?

Not all lenses perform equally well across every wavelength. Many standard lenses are optimised for visible light, whereas infrared or ultraviolet applications require dedicated optics.

Different wavelengths can cause focus shifts or changes in image quality. Therefore, optics and lighting should always be considered together during system design.

Common mistakes when selecting lenses

Many projects encounter similar challenges. The lens is selected after the camera rather than based on the application, pixel size is overlooked, or lighting is only considered late in the design process.

Depth of field and spectral requirements are also frequently underestimated. These issues often result in unnecessary redesigns and reduced long-term system stability.

Want to ensure your lens selection is right for your application?

Discuss your requirements with our machine vision experts or review your complete system design together with our team.

Optics as part of the overall vision architecture

Selecting the right optics is not an isolated task but an integral part of overall system design. Success depends on the interaction between the camera, optics, lighting and software.

In practice, the careful optimisation of these components has the greatest impact on system performance. With our MORE Services, we support customers in designing and validating complete machine vision solutions.