What if the sensor doesn’t match the lens image plane?

A lens and a camera sensor must be properly matched to ensure optimal image quality. When a lens’s image plane does not align with the camera sensor, several optical issues can arise, leading to suboptimal performance and potential image defects.

Let’s first take a closer look at the concept of the lens image plane and the sensor. The lens image plane is the location where the lens projects the focused image of the scene being photographed. On the other hand, the sensor is the light-sensitive component of the camera that captures this projected image and converts it into a digital or analog signal. When these two elements are not properly matched, a series of issues can arise.

To illustrate this, we conducted an experiment using the TTL11.5 series lens, which is specifically designed for 11.5mm sensors. We paired it with a camera equipped with a 1.1” (17.6mm) sensor to assess the resulting image quality. As soon as the images were captured, a distinct problem became apparent. Dark corners, also known as vignetting, emerged around the edges of the image. This phenomenon occurs because the lens, designed for a smaller sensor size, is unable to project a uniformly illuminated image onto the larger sensor. The light rays from the lens are not spread out evenly across the entire surface of the larger sensor, leading to a reduction in light intensity at the corners. This not only detracts from the aesthetic appeal of the image but can also result in the loss of important details in those areas.

Now, let’s consider the opposite scenario. Suppose we use the STS18.5 series lens, which is originally designed to have a 45mm field of view, and pair it with a 2/3” (11mm) sensor. In this case, the actual field of view shrinks to only 26mm. This is a direct consequence of the large image plane of the lens being paired with a relatively small sensor. The lens, designed to project a wider image, has its projected area restricted by the smaller sensor. As a result, only a portion of the lens’s full potential field of view is captured by the sensor, effectively reducing the overall area of the scene that can be photographed. This not only limits the scope of the photography but also fails to fully utilize the capabilities of the lens, wasting its performance potential.

The implications of such mismatches extend beyond just the visual appearance of the images. In professional photography, where precision and quality are non-negotiable, a misaligned sensor and lens image plane can render the entire setup useless for certain applications. For example, in architectural photography, where capturing the full expanse of a building with uniform lighting and sharpness is crucial, the presence of dark corners can distort the representation of the structure. In wildlife photography, where a wide field of view may be necessary to capture the natural habitat of animals, a reduced field of view due to an incompatible lens-sensor combination can prevent the photographer from getting the desired shot.

Moreover, in the context of modern imaging technologies such as surveillance cameras and machine vision systems, the consequences of a mismatch can be even more severe. Surveillance cameras rely on clear, distortion-free images to effectively monitor an area. Dark corners or a reduced field of view can create blind spots, compromising the security of the monitored location. In machine vision applications, where cameras are used for tasks such as quality control in manufacturing, an inaccurate lens-sensor combination can lead to incorrect measurements and faulty analysis, potentially resulting in significant financial losses for the company.

So, how can one ensure a proper match between the lens and the sensor? Camera and lens manufacturers typically provide detailed specifications regarding the compatibility of their products. These specifications include information about the sensor size, the lens's image circle (the area of the projected image), and the recommended applications for each lens-sensor combination. It is essential for photographers and users of imaging systems to carefully study these specifications before making a purchase.

In addition to relying on manufacturer specifications, some photographers also engage in practical testing. They may borrow or rent lenses and sensors to test different combinations in real-world shooting conditions. This hands-on approach allows them to directly observe the effects of different pairings and make an informed decision based on their specific needs. For example, a landscape photographer may test various lens-sensor combinations to find the one that offers the widest field of view without sacrificing image quality at the corners.

Another aspect to consider is the technological advancements in the field of lens and sensor design. In recent years, manufacturers have been working on developing more flexible and adaptable lenses and sensors. Some lenses are now designed with variable image circles, allowing them to be used with a wider range of sensor sizes. Similarly, sensors are being developed with improved light-gathering capabilities and more efficient pixel arrangements, which can help mitigate some of the issues associated with a mismatch. However, despite these advancements, it is still crucial to ensure a proper match to achieve optimal results.

The issue of lens-sensor compatibility also has implications for the future of the photography and imaging industry. As technology continues to evolve, new types of sensors and lenses are constantly being introduced. For instance, the development of high-resolution sensors with smaller pixel sizes and larger overall dimensions requires lenses that can accurately project a high-quality image onto these advanced sensors. Manufacturers need to collaborate closely to ensure that their lenses and sensors are designed to work in harmony. This collaboration could involve sharing technical knowledge, conducting joint research and development projects, and standardizing certain aspects of lens-sensor compatibility.

There is also a growing demand for products that can help bridge the gap between incompatible lenses and sensors. For example, some companies produce adapter rings that can modify the physical connection between a lens and a sensor, allowing for a wider range of combinations. However, it is important to note that while these adapters can sometimes enable a connection, they may not always fully address the optical and image-quality issues associated with a mismatch.

Furthermore, the education and training of photographers and imaging professionals play a vital role in understanding the importance of lens-sensor compatibility. Photography courses at educational institutions should include in-depth modules on the technical aspects of lenses and sensors, including how to select the right combination for different types of photography. Workshops and seminars can also be organized to provide hands-on experience and practical advice on this topic.

In conclusion, the relationship between the sensor and the lens image plane is a complex and multi-faceted one. A mismatch between these two elements can lead to a variety of problems, from dark corners and reduced field of view to compromised image quality and wasted lens performance. Whether in professional photography, surveillance, or machine vision applications, ensuring a proper match is essential. By understanding the technical specifications, conducting practical tests, keeping up with technological advancements, and promoting education in this area, photographers and users of imaging systems can make more informed decisions and achieve the best possible results in their work. As the industry continues to evolve, the importance of this harmonious relationship will only become more pronounced, driving further innovation and collaboration in the field of photography and imaging technology.

Basson focuses on machine vision products used for precision measurement and defect detection.

Basson not only provides high-precision bi-telecentric lens systems, telecentric lens systems, telecentric light sources, coaxial illuminations and optical lenses, but also offers customized services.

With products designed in Germany, business planned in the UK and products made in China, Basson is able to provide superior products to customers through its global team. Currently, Basson is in preparation of production and assembly of products in Japan.

Dr. Liu Lu, acting as CTO of Basson, is a PhD degree holder of Oxford University.

Production and testing instruments include optical vacuum coating machines manufactured by Satis in Switzerland and Leybold in Germany, a laser interferometer from Zygo in the US, a spectrophotometer from PerkinElmer in the US, a spherometer from Hofbauer Optik in Germany, a centering instrument from Kyoritsu Electric in Japan, a NC grinding device made by Kojima Engineering in Japan and an automatic centering machine made by Shonan in Japan.