The Magic Behind Camera Glass Manufacturing

Camera lenses are made of optical glass or plastic, and they work by focusing light rays through refraction. The process of creating a lens involves mixing glass powder, melting it into a liquid, and then squeezing it into a long glass strip. Small squares are then cut out and placed in a mold to be melted in an oven. The squares are then assembled into the lens body. Lenses need to be specially optimised to minimise aberrations, which are defects in the lens that cause blurring, colour changes, and distortion of lines.

Glass is ground and polished to a concave or convex shape

Camera lenses are made of optical glass or plastic. They are ground and polished to a concave or convex shape to focus light rays by refracting or bending them so that they meet or converge at a common point. A simple lens sees well through its centre, but its vision around the edges tends to blur. Blurring, colour changes, distortion of lines, and colour halos around objects are caused by defects in the lens called aberrations.

The concave lens is ground and polished to curve inward from the centre, while the convex lens is shaped to bulge outward from the centre. The concave lens is also known as a negative or diverging lens, while the convex lens is referred to as a positive or converging lens. The concave lens is used in movie projectors to spread out the image onto the screen, while the convex lens is used in magnifying glasses and some binoculars.

The process of grinding and polishing lens elements involves using a curve generator machine that is a first-step grinder. The lens then goes through a sequence of processes in which it is ground by polishing particles in water. The polishing particles become smaller in each step as the lens is refined. Curve generation and subsequent grinding vary in speed depending on the frailty, softness, and oxidation properties of the optical materials. After grinding and polishing, the elements are centred so that the outer edge of the lens is perfect in circumference relative to the centre line or optical axis of the lens.

Glass is coated to reduce abrasion and flare

Coatings are also applied to prevent image duplication, and the transmission of non-image light to the image, which are known as ghosts and flares, respectively. Ghosts are faint second images that are slightly displaced from the primary image. Flares appear when light from the back of the lens barrel is reflected from the lens surface onto the image.

Coatings are made from materials such as magnesium fluoride, calcium fluoride, silicon monoxide, and various metal oxides. These coatings are applied using techniques such as vacuum deposition or plasma sputtering. The thickness of the coating is important, as it determines the wavelength of light that will be suppressed. If the thickness of the coating is one-quarter of the wavelength of the light to be suppressed, then the light reflected by the coating surface and the lens surface will cancel each other out, reducing the overall amount of reflected light.

In addition to reducing reflection, coatings can also be used to filter light. For example, lenses coated to reflect ultraviolet light are used in eyeglasses and sunglasses. It is also possible to create coatings that only allow light of a specific wavelength to pass through. This is used in video cameras, where light is split into red, green, and blue elements before being converted into electrical signals to form an image.

Glass is assembled into the lens body

The process of assembling a camera lens is intricate and requires precision. Here is a detailed description of the steps involved in assembling the lens body:

Firstly, the glass powder is mixed in a large mixer and then melted into a liquid state. This liquid glass is then squeezed and moulded into a long glass strip. From this strip, small squares of glass are cut out with precise measurements. These squares are then placed in a mould and melted in an oven to create the desired shape for the lens elements.

The next critical step is to assemble the lens body with the glass inside. This stage involves mounting the lens elements into the lens barrel, ensuring perfect alignment and positioning. The lens barrel, or chassis, is responsible for supporting the various lens elements and is designed with specific tolerances to ensure optimal performance.

The lens body assembly also includes adding other essential components, such as the diaphragm and autofocus module. The diaphragm, or aperture, controls the amount of light passing through the lens and is constructed using curved metal leaves that can open or close to adjust the aperture size. The autofocus module, on the other hand, enables automatic focus adjustment.

During the assembly process, it is crucial to ensure that the lens elements are centred accurately. Centring ensures that the outer edge of the lens is perfectly aligned relative to the centreline or optical axis. This step is vital for the overall performance of the lens.

Once the glass is assembled into the lens body, the lens undergoes rigorous testing to ensure it meets the design standards for optical resolution, mechanical function, and autofocus response. These tests include evaluating the lens under varying temperature and environmental conditions, at different aperture settings, and across all focal lengths for zoom lenses.

Lens body is assembled with other parts

The lens body is assembled with other parts, including the diaphragm and autofocus module, which are produced as subassemblies. The diaphragm is constructed of curved leaves cut out of thin sheets of metal, held in place by two plates. One plate is fixed, while the other is movable, with slots for sliding pins. These pins slide the leaves back toward the barrel to open the diaphragm or into the centre to close the opening as the f-stop ring is turned.

The lens mount, which is typically made of brass, aluminium, or plastic, is also attached during assembly. Metal mounts are more durable, maintain their dimensions, can be machined more precisely, and allow for the replacement of elements if needed. On the other hand, plastic mounts are more lightweight and less expensive. The interior surfaces of the barrel are coated to protect them from damage and prevent internal reflection and flare.

After the lens mount is attached, the autofocus is added, the optical elements are positioned, and the lens is sealed. The final assembly is then rigorously adjusted and inspected to ensure it meets the design standards for optical resolution, mechanical function, and autofocus response. This includes testing the lens under varying temperature and environmental conditions, at every aperture position, and at every focal length for zoom lenses. Some lenses are also aged rapidly in laboratory tests to evaluate their durability.

Lens is tested and inspected

The lens of a camera is an essential component, responsible for capturing images by focusing light rays onto the camera's sensor or film. To ensure optimal performance, it is crucial to thoroughly test and inspect the lens during the manufacturing process. Here is a detailed overview of the testing and inspection procedures:

Testing the Lens Assembly

The camera lens assembly is meticulously tested to ensure it meets the required standards. This includes evaluating the lens under varying temperature and environmental conditions, testing it at different aperture settings and focal lengths, and capturing images of target charts and field conditions with varying lighting. Some lenses are also subjected to accelerated ageing tests to assess their durability.

Evaluating Image Quality

The quality of the lens significantly impacts the image formation on the camera's sensor. To assess this, manufacturers use specialised test charts and fixtures to evaluate various factors, including sharpness, chromatic aberration, lens flare, and geometric calibration.

Inspecting for Physical Damage

It is essential to inspect the lens elements for any physical damage or defects. This includes checking for decentering, where the elements may be misaligned, causing variations in image sharpness across the frame. Other potential issues are physical damage to the lens elements, sticky aperture blades, excessive dust or debris between the elements, and problems with the zoom or focus mechanisms.

Testing Aperture Performance

The aperture blades of the lens need to move smoothly and accurately. Tests are conducted to ensure that the blades move into position consistently and that the aperture maintains the correct shape. This is crucial for maintaining image quality, especially at high frame rates where the aperture mechanism is under greater demand.

Checking for Dust, Fungus, and Scratches

A good point light source, such as a dedicated inspection light, is used to check the front and rear lens elements for dust, scratches, or fungus. This inspection also includes checking the coating on the lens elements for any damage that could lead to issues with flare.

Evaluating Zoom, Focus, and Stabilisation Mechanisms

The zoom and focus mechanisms of the lens are tested to ensure smooth and easy movement. This includes checking for any grit in the mechanism, testing the focus ring for smoothness, and evaluating the image stabilisation system to ensure it functions correctly and "docks" properly when turned off.

Final Inspection

Before the lens is approved for release, it undergoes a rigorous final inspection. This includes testing the lens for optical resolution, mechanical function, and autofocus response. The lens may also be subjected to stress tests, such as shocks, drops, and vibration, to ensure its durability.

By following these comprehensive testing and inspection procedures, manufacturers can ensure that their camera lenses meet the required standards and deliver the best possible performance to photographers.

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