May. 27, 2024
Apochromatic (APO) and achromatic lenses exhibit noticeably higher image quality when compared to conventional lenses with the same speed and focal length. However, these lenses differ in terms of what they do and their effects. This article will cover apochromatic vs achromatic lenses and their advantages and disadvantages.
An achromatic lens is created by joining together two lenses of differing focal powers in a way that the resulting image is unaffected by color fringing or other chromatic aberrations. The most popular and oldest achromatic lens is the achromatic doublet, which is a set of two lenses, one convex and one concave, used to correct color aberrations.
Manufacturers use crown glass to craft the convex lens. It equalizes the distance at which the blue and red wavelengths fall on the focal plane, correcting their differences. This lessens the chromatic aberration for two wavelengths and spherical aberration for one wavelength.
Apochromatic lenses are composed of three lenses and are sometimes referred to as an apochromatic triplet. Compared to monochromatic and achromatic lenses, they offer superior correction of aberration and significantly reduce the amount of dispersion.
It corrects for two wavelengths in order to reduce spherical aberration, and it corrects for three wavelengths in order to minimize chromatic aberration. The wavelengths that it corrects are blue, red, and green. In addition to this, these lenses are made up of fluoride elements of some kind, flint glasses, and specialized lens coatings, all of which work together to focus the different wavelengths into one focal plane.
As with all optical components, achromatic lenses come with their own set of strengths and weaknesses. Here we explore a few of their pros and cons.
The achromatic lens significantly improves image clarity and brightness by eliminating color fringing, which is notably beneficial in polychromatic imaging.
While advanced versions of achromatic lenses are available, they are often cost-prohibitive. The basic achromatic lens remains the most economical option for sharp white light imaging and addresses a variety of common imaging requirements. Achromatic lenses perform best in pairs for finite conjugate applications, but their main objective is to accommodate infinite conjugate ratios.
When employed for finite conjugate applications, both the object and image are at a fixed distance from the lens. Consequently, their main role is to reduce or eliminate chromatic aberration. It's noteworthy that high-quality achromatic lenses can be sourced directly from reputable manufacturers.
Unlike singlet lenses, achromatic lenses maintain their on-axis performance regardless of the aperture size, enabling full utilization of available light.
Despite their benefits, achromatic lenses are not without flaws. Here is one downside to consider:
The secondary spectrum's profile and magnitude vary with focal length and lens type. Higher aperture (speed) lenses with longer focal lengths suffer more from secondary spectrum, degrading image quality.
In extreme cases, the secondary spectrum can limit image quality, necessitating the use of an apochromatic lens for optimal results.
Similar to achromatic lenses, apochromatic (APO) lenses come with their own benefits and drawbacks. Here is an overview of both.
APO lenses greatly enhance overall image quality by improving color contrast and sharpness. They also reduce eye strain, allowing for longer viewing periods.
By focusing light from three different frequencies, APO lenses provide superior chromatic and spherical aberration correction compared to achromatic lenses.
Having discussed their advantages, let’s examine some of the limitations of APO lenses:
The production of apochromatic lenses is expensive owing to the complex manufacturing processes and high-quality materials required. Consequently, these lenses are mostly found in high-end devices.
Though designed to minimize weight with three components, APO lenses are still heavier than most achromatic lenses due to the dense glass elements used.
Achromatic and apochromatic lenses play a crucial role in optics. Achromatic lenses bring two wavelengths to the same focal plane, whereas apochromatic lenses align three wavelengths.
Both types of lenses offer significant benefits such as enhanced image quality and superior light transmission. However, they also come with limitations like the secondary spectrum in achromatic lenses and the high cost of apochromatic lenses.
Understanding these differences can help you make an informed choice based on your specific requirements and budget.
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An achromatic lens can be defined as a lens which is made by a combination of two different types of lenses carrying different focal powers in a manner such that the images formed by the light of both the combined lenses are free from chromatic aberration or achromatism.
The most commonly used and the earliest example of an achromatic lens is the achromatic doublet. An achromatic doublet is made from a pair of glasses, of which one is typically a concave and another is convex. The concave element of the doublet is composed of flint glass (with higher dispersion); the convex element, however, is made up of crown glass (with low dispersion). These two elements are placed (cemented) next to each other in such a manner that the chromatic aberration of the one element is balanced by the chromatic aberration of another. There are various types of achromatic lenses, which differ in the type of lens elements and optical properties. Some examples of achromatic lenses include Clark doublet, Dialyte, Steinheil doublet, Littrow doublet and Oil-spaced doublet.
Understanding Achromatic Lenses
An achromatic lens, also known as an achromat, typically comprises two optical components cemented together—usually a positive low-index (crown) element and a negative high-index (flint) element. This design provides additional freedom compared to a single-element lens, or singlet, allowing for further performance optimization. Consequently, an achromatic lens offers noticeable advantages over a comparable diameter and focal length singlet.
An achromatic lens comes in various configurations, including positive, negative, triplet, and aspherized forms. It is essential to note that an achromatic lens designed for visible wavelengths can be a doublet (two elements) or triplet (three elements). However, the number of elements does not correlate with the number of colors it corrects. An achromat designed for visible wavelengths corrects for red and blue, regardless of whether it is a doublet or triplet configuration.
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Redirect to Optical Lens Parameters: Please check the parameters of the achromatic lens based on the table provided below:
Diameter (Dia.)
Radius of Curvature (R)
Edge Thickness (ET)
Effective Focal Length (EFL)
Center Thickness (CT)
Principal Point (P)
Back Focal Length (BFL)
Understanding Achromatic Lens Optical Performance
Because the on-axis performance of an achromatic lens does not deteriorate with larger clear apertures, "stopping down" the optical system becomes unnecessary. Stopping down refers to reducing the aperture size to enhance performance. When the entire clear aperture is utilized, an achromatic lens and lens systems using achromatic lenses are faster, more efficient, and more powerful than equivalent systems using singlet lenses.
Achromatic lenses are ideal for various applications including fluorescence microscopy, image relay, inspection, and spectroscopy. They are widely used in multi-lens optical systems, which often consist of several achromatic lenses. Achromatic lenses are also employed in high-quality microscopes and photographic devices within complex lens systems that eliminate both hyperchromatic and other monochromatic aberrations.
Achromatic lenses bring color into focus at the same points, allowing users to focus accurately on images. Compared to non-corrected singlet lenses, achromatic lenses produce much clearer images, making viewing easier and perception more precise.
Achromatic lenses have revolutionized imaging processes. Although lenses continue to evolve, the achromatic lens remains a fundamental component in both scientific and non-scientific optics applications.
+ Enhanced Image Quality:
By eliminating color fringes, the achromatic lens greatly increases image brightness and clarity. This improvement is particularly significant for polychromatic imaging.
+ Efficient Light Transmission:
Unlike singlet lenses, achromatic lenses maintain on-axis performance as the aperture size increases, enabling the use of the full clear aperture.
+ Cost-effective Production:
Although advanced achromatic lenses exist, they are significantly more expensive. For most purposes, the basic achromatic lens offers sufficient corrections, making it the most cost-effective means to obtain clear white light images.
Achromatic lenses are designed for infinite conjugate ratios but are suitable for finite conjugate applications when used in pairs. In finite conjugate applications, both the object and image are a finite distance from the lens pair, primarily to minimize or eliminate chromatic aberration. You can buy high-quality achromatic lenses from leading manufacturers.
What is an achromatic lens used for?
An achromatic lens is designed to control the effects of chromatic distortion or aberration, ensuring that the focus of all colors converges at the same point. These lenses are commonly referred to as 'achromats.'
What is the difference between achromatic and apochromatic?
Achromatic lenses are corrected to bring two wavelengths, typically red (~0.590 μm) and blue (~0.495 μm), into focus on the same plane. Apochromatic lenses are designed to align three colors, usually red (~0.620 μm), green (~0.530 μm), and blue (~0.465 μm), into focus on the same plane.
What does an achromatic lens consist of?
An achromatic lens typically consists of two optical components cemented together: a positive low-index (crown) element and a negative high-index (flint) element.
What is the meaning of achromatic?
Achromatic means "without color." It refers to either achromatic colors (greys or neutral colors like black or white) or an achromatic lens designed to minimize chromatic aberration.
How does an achromatic lens work?
An achromatic lens combines concave and convex glass pieces to focus different color wavelengths in light onto a single plane. Each glass type disperses colors differently; together, they counterbalance each other to produce a sharp image.
How do you make an achromatic lens?
An achromatic doublet is typically made of positive crown glass whose power is positive but decreases toward the red, cemented to a weak flint glass lens whose power is negative but similarly decreases (in magnitude) toward the red.
VY Optoelectronics Co., Ltd. is a professional manufacturer specializing in optical lenses, situated in Changchun City, China. Our factory produces nearly 50,000 achromatic lenses monthly, and we hold a large inventory of lenses. We also offer a full range of inspection reports and Certificates of Conformance (CoC) covering aspects such as surface quality, dimensions, centricity, coating transmittance, reflectance, and overall or partial surface accuracy. We process materials like optical glass, UV fused silica (JGS1), infrared fused silica (JGS3), calcium fluoride (CaF2), barium fluoride (BaF2), and other crystalline materials.
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