The specific parameters of plano-concave lenses may vary depending on the application scenarios and manufacturers. Below, we list some common parameter ranges or typical values from several aspects such as optical dimensions, surface quality, and material properties for you.

Optical Parameters

Focal Length

Common Range: -50 mm to -500 mm. For example, in simple optical experiments, lenses with focal lengths of -100 mm or -200 mm may be used; in special optical systems, the focal length may reach -500 mm or even larger negative values.

Accuracy: The precision of focal length typically ranges from ±1% to ±5%. High-precision optical systems require accuracy within ±1%, while general applications may tolerate ±5%.

Refractive Index

The refractive index varies depending on the material. Common optical glass like K9 has a refractive index of approximately 1.5163, while fused silica glass has a refractive index of about 1.458. For applications demanding higher optical performance, special glass materials with higher and more uniform refractive indices may be used.

Abbe Number

The Abbe number of K9 glass is approximately 64.17, making it a low-dispersion material; whereas flint glass typically has an Abbe number between 25–45, indicating higher chromatic dispersion. In systems requiring chromatic aberration correction, materials with appropriate Abbe numbers are selected and combined.

Transmittance

Uncoated Lenses: Transmittance is generally 90%–92% due to inherent absorption and surface reflection losses.

Coated Lenses: With anti-reflective (AR) coatings, transmittance can increase to 95%–99%. In laser systems, multilayer AR coatings are often used to achieve near-99% transmittance at specific wavelengths.

Dimensional Parameters

Diameter

Common Sizes: 6 mm, 12.7 mm, 25.4 mm, 50.8 mm, etc. Smaller diameters (e.g., 6 mm or 12.7 mm) are used in compact optical instruments, while larger diameters (e.g., 50.8 mm or more) are employed in large-scale equipment or experiments.

Tolerance: Diameter tolerance is typically ±0.05 mm–±0.2 mm. High-precision systems may require tighter control (e.g., ±0.05 mm).

Center Thickness

Range: 1 mm–10 mm. Thinner lenses (e.g., 1–3 mm) suit weight/volume-constrained applications, while thicker lenses (e.g., 5–10 mm) are used for higher strength or specialized optical designs.

Tolerance: Center thickness tolerance is usually ±0.1 mm–±0.2 mm.

Surface Quality Parameters

The number of flatness

It is generally required to be within 1 to 3. The number of flatness reflects the degree of deviation between the lens surface and the ideal spherical surface. The smaller the value, the closer the surface is to the ideal spherical surface. In high-precision optical imaging systems, it is usually required that the number of flatness be within 1.

The local aperture error

It is usually controlled between 0.1 and 0.5. Local aperture error describes the deviation of a local area on the lens surface. Strictly controlling the local aperture error helps improve the imaging quality of the optical system.

The surface roughness

 It is generally required to reach Ra 10-20nm (Ra is the arithmetic mean deviation of the contour). In some optical applications with extremely low scattering requirements, the surface roughness may need to be achieved Ra is 5nm or even lower.