Spherical Lens Selection Guide - Optics - Newport

Plano-Convex Lenses are the best choice for focusing parallel rays of light to a single point, or a single line in the case of cylindrical lenses. This lens can be used to focus, collect and collimate light. It is the most economical choice for demanding applications. The asymmetry of these lenses minimizes spherical aberration in situations where the object and image are located at unequal distance from the lens. The optimum case is where the object is placed at infinity (parallel rays entering lens) and the final image is a focused point. Although infinite conjugate ratio (object distance/image distance) is optimum, plano-convex lenses will still minimize spherical aberration up to approximately 5:1 conjugate ratio. For the best performance, the curved surface should face the largest object distance or the infinite conjugate to reduce spherical aberration.

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Bi-Convex Lenses are the best choice where the object and image are at equal or near equal distance from the lens. When the object and image distance are equal (1:1 magnification), not only is spherical aberration minimized, but also coma, distortion, and chromatic aberration are identically canceled due to the symmetry. Bi-convex lenses function similarly to plano-convex lenses in that they have a positive focal length, and focus parallel rays of light to a point. Both surface are spherical and have the same radius of curvature, thereby minimizing spherical aberration. As a guideline, bi-convex lenses perform within minimum aberration at conjugate ratios between 5:1 and 1:5. Outside this magnification range, plano-convex lenses are usually more suitable.

Plano-Concave Lenses are the best choice where object and image are at absolute conjugate ratios greater than 5:1 and less than 1:5 to reduce spherical aberration, coma, and distortion. Plano-Concave lenses bend parallel input rays so they diverge from one another on the output side of the lens and hence have a negative focal length. The spherical aberration of the Plano-Concave lenses is negative and can be used to balance aberrations created by other lenses. Similar to the Plano-Convex lenses, the curvature surface should face the largest object distance or the infinite conjugate (except when used with high-energy lasers where this should be reversed to eliminate the possibility of a virtual focus) to minimize spherical aberration.

Bi-Concave Lenses are the best choice where object and image are at absolute conjugate ratios closer to 1:1 with converging input beam. The output rays appear to be diverging from a virtual image located on the object side of the lens; the distance from this virtual point to the lens is known as the focal length. Similar to the Plano-Concave lenses, the Bi-concave lenses have negative focal lengths, thereby causing collimated incident light to diverge. Bi-Concave lenses have equal radius of curvature on both side of the lens. They are generally used to expand light or increase focal length in existing systems, such as beam expanders and projection systems.

Positive Meniscus Lenses are designed to minimize spherical aberration and are generally used in small f/number applications (f/number less than 2.5). The Positive Meniscus Lenses have a larger radius of curvature on the convex side, and a smaller radius of curvature on the concave side. They are thicker at the center compared to the edges. Positive meniscus can maintain the same angular resolution of the optical system while decreasing the focal length of the other lens, resulting a tighter focal spot size. A positive meniscus lens can be used to shorten the focal length and increase the numerical aperture of an optical system when paired with another lens. For the best performance, the curved surface should face the largest object distance or the infinite conjugate to reduce spherical aberration.

Spherical Lens Material Options

Lens Type N-BK7 UV Fused Silica CaF2 MgF2 ZnSe Crown/Flint Plano-Convex Bi-Convex Plano-Concave Bi-Concave Achromatic Doublet Cylindrical Lenses Plano-Convex Plano-Concave

Coatings

Optical coatings are generally applied as a combination of thin film layers on optical components to achieve desired reflection/transmission ratio. Important factors that affect this ratio include the material property used to fabricate the optics, the wavelength of the incident light, the angle of incidence light, and the polarization dependence. Coating can also be used to enhance performance and extend the lifetime of optical components, and can be deposited in a single layer or multiple layers, depending on the application. Newport’s multilayer coatings are incredibly hard and durable, with high resistance to scratch and stains.

Anti-Reflection Coating (AR coating)

Newport offers an extensive range of antireflection coatings covering the ultraviolet, visible, near infrared, and infrared regions. For most uncoated optics, approximately 4% of incident light is reflected at each surface, resulting significant losses in transmitted light level. Utilizing a thin film anti-reflection coating can improve the overall transmission, as well as minimizing stray light and back reflections throughout the system. The AR coating can also prevent the corresponding losses in image contrast and lens resolution caused by reflected ghost images superimposed on the desired image.

Newport offers three types of AR coating designs to choose from, the Single Layer Magnesium Fluoride AR coating, the Broadband Multilayer AR coating, and Laser Line AR V-coating. A single layer Magnesium Fluoride AR coating is the most common choice that offers extremely broad wavelength range at a reasonable price. It is standard on achromats and optional on our N-BK7 plano-convex spherical lenses and cylindrical lenses. Comparing to the uncoated surface, the MgF2 provides a significant improvement by reducing the reflectance to less than 1.5%. It works extremely well over a wide range of wavelengths (400 nm to 700 nm) at angles of incidence less than 15 degrees.

Broadband Multilayer AR coating improves the transmission efficiency of any lens, prism, beam-splitter, or windows. By reducing surface reflections over a wide range of wavelengths, both transmission and contrast can be improved. Different ranges of Broadband Multilayer AR coating can be selected, offering average reflectance less than 0.5% per surface. Coatings perform efficiently for multiple wavelengths and tunable laser, thereby eliminating the need for several sets of optics.

V-coatings offer the lowest reflectance for maximum transmission. With its high durability and high damage resistance, Laser line AR V-coating can be used at almost any UV-NIR wavelength with average reflectance less than 0.25% at each surface for a single wavelength. Valuable laser energy is efficiently transmitted through complex optical systems rather than loss to surface reflection and scattering. The trade off to its superior performance is the reduction in wavelength range. AR.33 for nm is available from stock on most Newport lenses. All other V-coating can be coated on a semi-custom basis.

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Coating Wavelength Range
(nm) Reflectance Cost Features AR.10
Broadband
245–440 Ravg <0.5% Moderate Only available on UV fused silica lenses MgF2
Broadband
Broadband
400–700 Ravg <1.5% Low Available on achromats, KPX series, and Cylindrical lenses AR.14
430–700 Ravg <0.5% Moderate Best choice for broadband visible applications AR.15
Broadband
250–700 Ravg <1.5% Moderate Great choice for broadband UV to visible applications AR.16
Broadband
650– Ravg <0.5% Moderate Excellent for NIR laser diode applications AR.18
Broadband
– Ravg <0.5% Moderate Ideal for telecom laser diode applications V-Coat Multilayer, AR.27 Laser Line
532 Rmax <0.25% High Highest transmission at a single wavelength V-Coat Multilayer, AR.28 Laser Line
632.8 Rmax <0.25% High Highest transmission at a single wavelength AR.33
Laser Line
Rmax <0.25% Moderate Highest transmission at a single wavelength

Optical instruments have revolutionized the way we perceive and interact with the world around us. Among the various components that make these instruments functional, double concave lenses play a vital role. With their unique structure and optical properties, double concave lenses find applications in a wide range of optical instruments. In this blog, we will delve into the fascinating applications of double concave lenses and explore their contributions to the field of optics.

1. Microscopes

Microscopes have significantly advanced our understanding of the microscopic world. Double concave lenses are used in microscope objectives to correct aberrations and improve the quality of magnified images. These lenses aid in focusing light onto the specimen, allowing researchers to observe fine details and enhance the resolution of the microscope.

2. Telescopes

Telescopes have enabled us to explore distant celestial objects and unravel the mysteries of the universe. Double concave lenses find application in the eyepiece of telescopes, where they help in magnifying and focusing the image formed by the primary lens or mirror. By adjusting the distance between the double concave lens and the eye, the telescope’s magnification and field of view can be customized for optimal viewing experience.

3. Cameras and Photography

In the realm of photography, double concave lenses are used in camera lenses to correct optical aberrations and achieve high-quality images. These lenses help in focusing light onto the camera’s image sensor, allowing photographers to capture sharp and detailed photographs. Double concave lenses are also employed in zoom lenses to control the focal length and provide variable magnification capabilities.

4. Projectors

Projectors are widely used in educational institutions, businesses, and entertainment venues. Double concave lenses are employed in projectors to expand and focus the light beam onto the projection screen. By manipulating the distance between the lens and the light source, the size and focus of the projected image can be adjusted, enabling large-scale presentations and immersive visual experiences.

5. Spectacles and Eyeglasses

For individuals with specific vision impairments, double concave lenses can be incorporated into spectacles and eyeglasses. These lenses help to correct myopia (nearsightedness) by diverging light rays before they reach the eye, enabling the formation of clear images on the retina. The precise curvature and thickness of the double concave lens are tailored to the individual’s prescription, ensuring optimal vision correction.

6. Collimators and Optical Instruments Calibration

Collimators are essential tools in optical alignment and calibration. Double concave lenses are utilized in collimators to create a parallel beam of light for alignment purposes. The lenses help in generating a diverging light beam, which can be precisely controlled and used to calibrate and align other optical instruments such as lasers, spectrometers, and interferometers.

7. Laser Beam Expanding

In laser applications, double concave lenses are utilized for beam expanding purposes. By positioning the lens appropriately, the laser beam diameter can be increased, spreading the light over a larger area. This expansion helps to control the beam’s divergence and enables applications such as laser cutting, laser engraving, and laser marking.

8. Optical Systems Simulation

Double concave lenses are used in optical systems simulation to mimic the behavior of real-world optical components. By integrating double concave lenses into optical simulation software, engineers and researchers can model and analyze the performance of various optical systems, such as cameras, microscopes, telescopes, and projectors, before their physical implementation.

Conclusion:

Double concave lenses have a remarkable range of applications in optical instruments, contributing to advancements in microscopy, telescopes, cameras, projectors, eyeglasses, collimators, laser systems, and optical system simulation. Their ability to correct aberrations, focus light, and control the direction of light rays makes them indispensable in the world of optics. As technology continues to progress, double concave lenses will undoubtedly play a pivotal role in shaping the future of optical instruments and our understanding of the world around us.

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