Sun Lens Manufacturer

The impact of Sun Lens grinding on lenses

Sun lenses, typically referring to lenses that are tinted or polarized for outdoor use, undergo specific grinding processes that affect their optical and physical properties.

Curve generation and base curve selection: The grinding process begins with selecting an appropriate base curve for the front surface of the lens. For sun lenses, the base curve must account for the wrap of the frame, particularly in stylish or sportier designs. A mismatched base curve can induce optical distortion or reduce the effectiveness of polarization.

Thickness reduction and edge uniformity: Grinding the back surface to achieve the prescribed power removes material from the lens blank. For sun lenses, maintaining uniform thickness across the lens is important for consistent tint darkness. Variations in thickness can cause the tint to appear lighter in thinner areas and darker in thicker sections, creating an uneven cosmetic appearance.

Polarization axis alignment: If the sun lens is polarized, the grinding process must maintain precise orientation of the polarizing film within the lens. Even slight rotation during edging can misalign the filter, reducing its effectiveness in glare reduction. Laboratory technicians verify axis alignment before final cutting.

What distinguishes a stock lens from a custom lens?

A stock lens is fully manufactured with both front and back curves finished to a specific spherical or toric power. It awaits only edging to match a frame shape. A custom lens, by contrast, starts as a semi-finished blank with only the front curve pre-generated; the back surface is ground to the exact prescription after the order is received.

What are the advantages of stock lenses?

Stock lenses offer faster turnaround times because the optical work is already complete. They are typically available for common prescriptions within a certain range, often from -4.00 to +4.00 with a cylinder up to -2.00. For prescriptions within this range, stock lenses provide a cost-effective option.

Are there limitations?

Prescriptions outside the common range may not be available as stock lenses. Higher powers, high cylinder values, or prism requirements generally necessitate custom surfacing. Additionally, stock lenses offer limited options for material and design variations compared to custom lenses.

Can stock lenses be tinted?

Yes. Stock lenses made from materials compatible with tinting, such as CR-39 plastic, can be dipped in dye solutions to achieve solid tints or gradients.

Do stock lenses include coatings?

Some stock lenses come with factory-applied hard coatings or anti-reflective treatments. Others are uncoated and may receive coatings after edging, depending on the laboratory's capabilities.

How quickly can I receive stock lens glasses?

If the prescription falls within the stock range and the frame is in stock, glasses can often be completed within one to three days, as only cutting and mounting are required.

Are stock lenses available in polycarbonate?

Yes, polycarbonate stock lenses are common for prescriptions within the typical range, particularly for children's eyewear and safety frames.

How is a Tinted Single Vision Lens achieved?

Tinting a single vision lens involves adding color to the lens material or surface to reduce light transmission or achieve a specific cosmetic effect. Several methods exist, each suited to different lens materials and desired outcomes.

Dye immersion process for plastic lenses

Lenses made from CR-39 plastic are placed in a heated dye solution containing dispersed colorants.

The lens absorbs the dye, with darker tints achieved through longer immersion times.

Temperature is carefully controlled, typically between 180°F and 200°F, to ensure even absorption.

Gradient tints require controlled dipping and withdrawal rates to create the transition from darker to lighter areas.

In-mass tinting for certain materials

Some lens materials have color incorporated during the manufacturing of the raw lens blank.

The tint is uniform throughout the lens and cannot be removed or altered.

This method is common for sunglass lenses, where a consistent color across different prescriptions is desired.

The tint density remains unchanged even if the lens is ground to different thicknesses.

Vacuum coating for glass and polycarbonate

Glass lenses and some polycarbonate lenses that do not accept dye receive tint through thin-film coatings.

The lens is placed in a vacuum chamber where metallic oxides are deposited on the surface.

Layer thickness determines the final color and density of the tint.

This method allows for precise control of light transmission and reflective properties.

Polarized tint combinations

For polarized tinted lenses, the polarizing film is sandwiched between lens layers.

The tint may be incorporated into the film itself or added to one of the outer layers.

This approach combines glare reduction with specific light transmission levels.