When light from a strong light source (such as the sun or artificial light) reaches the lens directly, it reflects and bounces off various lens elements and even the sensor, thereby degrading image quality and creating unwanted artifacts in the image. This phenomenon is known as “glare,” and it can affect images in various ways, from significantly reducing image contrast by introducing colored haze, to adding circular or semi-circular halos or “ghosting,” or even strangely shaped translucent objects of various colors and intensities. In photography, glare can also be acceptable, for example, to add artistic elements to an image. Lens flare is also frequently added to movies and video games to increase realism and enhance the viewer's visual experience.

1. What is Lens Glare?
Lens glare occurs when a light source (such as the sun) is much brighter than the rest of the scene, either within the image (within the lens's field of view) or outside the image but still shining onto the lens. Depending on the position of this strong light source, it can cause significant haze/lack of contrast, spherical and polygonal artifacts, semi-circular shapes with rainbow colors, or a combination of all these scattered throughout the image. This is caused by internal reflections within the lens or even between the image sensor and the lens.

As shown in Figure 2, normal light rays (red) follow their normal path directly to the image plane (green), while strong light sources (blue) can split or reflect off lens surfaces, eventually reaching different parts of the frame (blue dashed lines). When light passes through the lens, it can also be reflected if obstructed, leading to more pronounced glare.

2. Veiling Glare
Veiling glare occurs when a strong light source is outside the lens's field of view, meaning the light source is not in the image, but its light still reaches the lens. This results in a very noticeable soft haze/lack of contrast, where dark areas of the frame become brighter and appear washed out. High-quality lenses with multi-coated lens elements help reduce veiling glare, but they come at a higher cost.

As shown in Figure 3, the sun is directly above the subject, outside the image area, but its light still reaches the lens, creating a hazy glow around the person in the photo. Veiling glare not only affects the area around the sun but also severely impacts the person's hair, face, and even clothing, resulting in reduced contrast. In this case, veiling glare is actually intentionally allowed, providing a moody, bright shot. Unfortunately, veiling glare can be exacerbated by various factors, such as dust inside the lens, dirty lens elements, dirty/low-quality filters, or the lack of anti-reflective multi-coating technology. In some cases, this effect looks poor in the image.

As shown in Figure 4, this lens is not suitable for shooting in sunlight, making the entire image look hazy with no visible details. This is partly due to the lack of multi-coating technology and partly due to dust accumulated inside the lens over time, causing additional reflections.

3. Ghosting
Unlike veiling glare, where the image looks hazy and has extremely low contrast, ghosting, or simply “ghosts,” refers to all visible “artifacts” in the image, whether they are reflections of a strong light source or shapes resembling the lens aperture. These spheres of different colors and shapes are usually aligned with the light source and can cover the entire image, with dozens of different “artifacts.”

In addition to the visible veiling glare in the image, circular “artifacts” can also be seen, which are called “ghosts.” The total number of these flares varies depending on the number of lens elements in the lens. Generally, the more lens elements, the more “ghosts” appear in the image.

4. Sensor/Red Dot Glare
Glare caused by light bouncing between the image sensor and the lens is called “red dot glare,” also known as “sensor glare.” Unlike lens glare, red dot glare is not just light reflected from the lens and aperture, but light reflected from the image sensor to the lens and then back to the image sensor.

In addition to the polygonal aperture ghosts shown in the illustration, a cluster of red dots around the sun can also be seen—these are the microlenses on the sensor, magnified in the image. 5. Factors Affecting Lens Glare

Although most modern lenses use special multi-coating technologies to reduce glare, even some professional-grade lenses can produce images with visible ghosting or even veiling glare. This is because the position of the light source in the image and the angle at which light reaches the lens have a significant impact on how it appears and its intensity in the image. There are also other factors, such as:

1. Lens elements—the more lens elements a lens has, the more prone it is to glare.

2. Focal length—wide-angle lenses are designed not only to handle glare well, but also the shorter the focal length, the smaller the light source appears. On the other hand, telephoto lenses perform much worse because they magnify everything, which is why telephoto lenses have huge/long lens hoods.

3. Lens design—good lens design certainly affects lens glare. Even without expensive coating technologies, glare and ghosting can be greatly reduced.

4. Multi-coating—multi-coated lens elements definitely have a huge impact on glare performance.

6. How to Avoid Lens Glare

1. Use a lens hood or your hand to block the light. Lens hoods exist for a reason, or placing your hand (or other objects) over the lens to block sunlight will eliminate glare; this is the simplest method.

2. Use high-quality lenses. Professional-grade lenses are expensive, but they come with amazing coating technologies that help significantly reduce or even eliminate glare issues.

3. Use prime lenses instead of zoom lenses. Prime lenses have simpler optical formulas than zoom lenses and definitely fewer optical elements. The fewer elements to deal with, the less glare appears in the image.

4. Change the position of the light source during shooting.

5. Filters—low-quality filters will cause more glare and ghosting issues in the image.

6. Lens dust—over time, lenses accumulate dust, and internal dust will cause more glare.

7. Fingerprints and other particles on the lens will also produce more glare/ghosting.

7. How to Test Glare

Yanding's self-developed Flare automated test equipment can test not only glare and ghosting but also FOV. Adding a guide rail allows for a wider range of adjustment for the distance between the camera and the light source. The equipment features a programmable two-axis rotary gimbal, capable of ±180° adjustment on the Raw axis and ±180° adjustment on the Roll axis, with an accuracy of up to 0.1°. It can be operated via a touch screen or connected to a computer for one-click operation, offering advantages such as selectable fine angle adjustments, fast response, precise angle control, and convenient operation.

1. Install the module, clamp it, and rotate it to face the glare point light source. Use infrared to make the infrared crosshair tangent to the surface of the module lens. At the same time, use the image capture card and fixture fine-tuning to align the module, as shown in the figure:

2. Adjust to a suitable distance, record the distance from the module to the point light source, rotate the two axes, observe the capture card screen, and capture the required glare image: the distance from the module to the point light source (recommended distance 680mm). Use the scale below to control the distance between the module and the light source.

3. Import the image into the RIQA image quality test software for analysis and obtain the data, as shown in the figure below.

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