Achromatic Lenses Guides of Knowledge, Cost and Manufactures

An achromatic lens is a type of optical lens designed to limit the effects of chromatic and spherical aberration. Chromatic aberration occurs when different wavelengths of light are refracted by different amounts, causing a failure to focus all colors to the same convergence point. This results in a blurred image with color fringes around the edges. Achromatic lenses are engineered to bring two wavelengths, typically red and blue, into focus in the same plane, thereby significantly reducing chromatic aberration.

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Achromatic lenses are usually made by combining two types of glass with different dispersion properties:

1. Crown Glass: A type of glass with low dispersion.
2. Flint Glass: A type of glass with high dispersion.

These two or more elements are cemented together to form a doublet lens. The combination of these materials helps to counteract the dispersion of light, effectively minimizing chromatic aberration.

Structure and Principle

A Positive Achromatic Lens is usually a doublet, made up of a positive low-refractive index element (such as crown glass) and a negative high-refractive index element (such as flint glass). This combination allows the chromatic aberration of one lens to be neutralized by the other, achieving the correction of chromatic aberration.

Applications

These lenses are widely used in fluorescence microscopy, image relaying, detection, and spectroscopy, among others. They provide almost constant focal lengths across a broad wavelength range, and compared to single lenses, they produce smaller light spots and clearer imaging.

Advantages

• Chromatic Aberration Correction: Effectively focuses two principal wavelengths of light, significantly reducing chromatic aberration.
• Improved Image Quality: Delivers clearer imaging and finer light spots compared to single lenses.
• Diverse Coating Options: Offers a selection of coatings such as VIS, NIR, SWIR to suit various application needs.

Manufacturing and Materials

Creation of Positive Achromatic Lenses involves the precise bonding of two selected materials, commonly N-BK7 and SF5 glass. The lens design parameters including radius of curvature, center thickness, and others are meticulously calculated to ensure optimal optical performance.

Typical Specifications (Example)

• Diameter: 50.80mm
• Effective Focal Length (EFL): 150.00mm
• Coating: Anti-Reflective Coating AR@400-700nm
• Materials: N-BK7/SF5
• Back Focal Length (BFL): 140.40mm
  Radius of Curvature (R1/R2/R3): 83.20mm, -72.10mm, -247.70mm respectively
• Center Thickness (CT): 15.00mm
• Surface Quality: Ranges from 40-20 to 60-40 depending on specifications

With precision imaging capabilities and chromatic aberration correction, Positive Achromatic Lenses are indispensable components in advanced optical systems, particularly in applications where image quality is of paramount importance.

Negative Achromatic Lenses are specially designed optical lenses for correcting chromatic aberrations, typically made by bonding two different types of glass materials—a low refractive index crown glass and a high refractive index flint glass. Unlike their counterpart, the Positive Achromatic Lenses, negative achromatic lenses primarily function to disperse, not focus, light rays.

Structure and Working Principle

The negative achromatic lens consists of a positive-dispersion crown glass lens paired with a negative-dispersion flint glass lens. The design aims to counteract the chromatic aberration produced by one lens with that produced by another, thus effectively correcting chromatic aberration. These lenses play a crucial role in various optical systems requiring light to diverge.

Application Fields

Negative achromatic lenses have a wide range of applications in optics, such as laser beam expanders, optical relay systems, and more. They offer a stable diverging angle across a wide wavelength and can produce a smaller and clearer spot and image compared to single lenses.

Advantages

1. Effective Chromatic Aberration Correction: The lens can disperse light rays of different wavelengths onto the same plane, significantly reducing chromatic aberration issues.
2. Superior Imaging Quality: Compared to single lenses, negative achromatic lenses provide clearer imaging quality and produce smaller light spots.
3. Diverse Configurations: Depending on different usage requirements, lenses can be configured with various coating options suitable for visible light, near-infrared (NIR), short-wave infrared (SWIR), and other wavelengths.

Manufacturing Materials

In production, negative achromatic lenses usually employ materials like N-BK7 and SF5. Lens manufacturing involves meticulous design of many parameters, such as the radius of curvature, center thickness, and edge thickness, to ensure optimal optical performance.

Typical Specifications

• Diameter: 50.80 mm
• Effective Focal Length: -150.00 mm
• Coating: Enhanced reflectivity coating for the 400-700 nm band
• Materials: Typically N-BK7 and SF5 glass
• Back Focal Length: -140.40 mm
• Radius of Curvature: R1 -83.20 mm, R2 72.10 mm, R3 247.70 mm
• Center Thickness: 15.00 mm
• Surface Quality: Varies from 40-20 to 60-40

Overall, negative achromatic lenses play a vital role in optical systems that require high precision diversion of light and correction of chromatic aberrations.

Contact us to discuss your requirements of Custom Optical Triplet Lenses. Our experienced sales team can help you identify the options that best suit your needs.

Achromatic Triplet Lenses represent an advanced optical technology specifically designed for the effective correction of chromatic aberrations and other types of optical anomalies. These lenses are composed of three distinct lens elements, typically two elements made of high refractive index materials encasing one made of a lower refractive index material. This arrangement not only significantly reduces aberrations, including distortion and spherical aberrations, but also provides clear, high-quality imaging results.

Structure and Working Principle

Achromatic Triplet Lenses usually feature a symmetrical three-element design, consisting of two high refractive index glasses (such as crown glass) and one low refractive index glass (like flint glass) bonded together through a precise adhesion process. This structural layout enables the lens to efficiently correct chromatic aberration and further reduce aberrations, such as pincushion distortion and spherical aberration, through its symmetry.

Application Areas

With their excellent imaging properties, Achromatic Triplet Lenses are extensively used in fields that demand high-quality imaging. These include fluorescence microscopy, spectroscopy, surface inspection, and life sciences imaging, among others. The lenses are capable of providing excellent color correction and high-resolution image quality across a wide wavelength range.

Advantages

1. Chromatic Aberration Correction: The Achromatic Triplet Lenses can precisely adjust light of different wavelengths to the same focal plane, significantly reducing the occurrence of chromatic aberrations.
2. Reduced Aberrations: Thanks to the ingenious symmetrical design and precise manufacturing processes, distortions such as pincushion distortion and spherical aberration are effectively controlled and minimized.
3. High-Resolution Imaging: These lenses offer high-definition and high-quality imaging solutions for a variety of precision optical applications.

Manufacturing Materials and Processes

The production of Achromatic Triplet Lenses involves the precise bonding of lenses made from different types of materials. Typical lens materials include traditional optical glass, ultraviolet-grade fused silica (JGS1), infrared-grade fused silica (JGS3), and calcium fluoride (CaF2), among others. Key lens parameters, such as the radius of curvature, central and edge thickness, are meticulously designed to ensure optimal optical performance.

Typical Specifications

• Manufacturing Materials: Various, including optical glass, ultraviolet-grade fused silica, infrared-grade fused silica, and calcium fluoride.
• Dimensional Tolerances: Typically, ±0.03mm for standard factory specifications, with precision manufacturing achieving up to ±0.01mm.
• Center Thickness Tolerance: ±0.03mm as the standard factory specification, with manufacturing limits reaching ±0.02mm.
• Radius of Curvature Tolerance: ±0.3% as the standard factory specification, with manufacturing limits reaching ±0.2%.
• Surface Quality: Achieving a 20-10 level under factory standards, improving to a 10-5 level for higher demands.
• Irregularity: The common standard is 1/5 Lambda, with the limit for higher demands being less than 1/10 Lambda.
• Centration Deviation: Under normal factory conditions, centration can be controlled within 3 arcminutes (Arcmin), with manufacturing limits tightening to 1 Arcmin.

Achromatic Triplet Lenses play a crucial role in modern optical systems, especially in applications requiring high-precision imaging and chromatic aberration correction. Their high-quality design and manufacturing make them the preferred choice for many advanced optical applications.

Aspheric Achromatic Lenses merge the advantages of both aspheric and achromatic lenses, creating a sophisticated optical component. This unique combination allows them to deliver exceptional image quality and precise chromatic aberration correction.

Structure and Working Principle

These lenses are typically composed by bonding together two lenses: one achromatic lens and one aspheric lens. The design of the aspheric lens is aimed at mitigating the wavefront errors produced by traditional spherical lenses, thereby achieving more accurate image quality, reducing the RMS spot size, and approaching the diffraction limit.

Manufacturing and Material Selection

Commonly, these lenses are made from photosensitive polymers and glass optical components, with the polymer applied to one surface of the bonded lens pair. This method not only enables the lenses to be manufactured quickly within a short timeframe but also offers flexibility similar to traditional multi-element assemblies. However, the working temperature range of Aspheric Achromatic Lenses is quite narrow, restricted from -20°C to +80°C, and they are not suitable for Deep Ultraviolet (DUV) spectral transmission.

Key Advantages

1. Chromatic Aberration Correction: They effectively correct chromatic aberration, precisely focusing light of different wavelengths onto the same plane.
2. Reduction of Aberrations: Their aspheric design significantly reduces spherical aberration and wavefront errors, enhancing image quality.
3. Cost-Effectiveness: Compared to conventional multi-element optical systems, these lenses provide greater value for money.

Application Areas

Aspheric Achromatic Lenses are widely used in various high-precision optical systems, such as:

• Fiber focusing or collimation
• Imaging relay systems
• Detection and scanning systems
• High numerical aperture imaging systems
• Laser beam expanders

Technical Specifications

• Materials: Photosensitive polymers and glass optical lenses
• Operating Temperature Range: From -20°C to +80°C
• Main Applications: Including fiber focusing, imaging relays, detection scanning, and high numerical aperture imaging, among others

With their ingenious design and efficient manufacturing process, Aspheric Achromatic Lenses demonstrate outstanding optical performance and a broad spectrum of applications, making them an indispensable key component in modern precision optics and vision systems.

Looking for a cost-effective achromatic lens manufacturer? Consider Chineselens Optics – a leading optical company based in China. We specialize in manufacturing achromatic lenses for a wide range of applications including: camera lenses, telescopes, and microscopes. Chineselens Optics has built a reputation in the industry for affordable pricing and superior product quality.
Whether it’s for your scientific research project, photographic hobby, instrumentation, or any situation where precise imaging is required, our achromatic lenses will provide you with excellent color correction and image clarity. Choose Chineselens Optics for quality optical solutions and services that will help your projects and products reach new heights. Contact our experts today for a consultation!

The company is the world’s best Optical Glass Lenses supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

Sidebar: Basic Optical Tube Design

My fifth grade daughter had a science assignment recently that required her to know that light can do 3 different things when it encounters an object:  it can bounce (be reflected), bend (be transmitted), or be absorbed (causing heat).    A telescope is designed to utilize one or two of these dynamics to refocus light onto your eyeball.   Diagram of three main telescope designs. Courtesy of Andrew Johnston at http://www.eaas.co.uk/ This gives rise to THREE different scope designs (above):  one that uses mirrors (reflectors), one that uses lenses (refractors), and one that uses BOTH mirrors and lenses (catadioptrics or "cats").   All of these designs require some way of mounting it, which is the subject of the previous SIDEBAR.  ​

One thing in common, regardless of the design, is that light has some distance to travel through the scope once it enters the scope.  More precisely, from the moment it hits the primary element, whether a mirror (in reflectors and cats) or a lens (in refractors), the light begins to be focused toward its "focal point."   This path from first contact (not including the corrector plate in an SCT) to the focal point is known as the focal length of the telescope.  The focal ratio (or f-number) will be the overall focal length divided by the scope's aperture.  In essence, this is a measure of how "steep" the cone of light is...or at what rate the light finds its focal point.

With lenses, where light can only be bent, it must travel along the full length of the optical tube and out the other end.   Thus, refractors are typically longer than most scopes at comparative aperture sizes.   With concave mirrored primaries, both the reflector and cat scope (most notably SCTs), will fold the light back in the direction the light came to hit a secondary mirror placed in the center of the scope's aperture end (see the note above on "central obstruction").  In a typical newtonian reflector, that smaller secondary mirror is also concave, angled 45 degrees to bounce the light out the side, a short distance to the eyepiece.  Compared to the refractor, the cutting-off of the light to the side of the scope as well as the typically short focal length of the primary mirror - lenses have typically longer focal lengths - means that the overall OTA of a newtonian reflector will often be shorter. 

A catadioptric, like a Schmidt (SCT) or Maksukov (Mak) Cassegrain, has a convex secondary mirror, which bounces light straight back toward the primary again, but this time the light "cone" is small enough to go through a hole in the primary and through the back of the telescope.   The eyepiece awaits on the back side of the scope.   In effect, the light has been twice folded back upon itself, which lends most "cats" the distinction of having a "folded" design.  More importantly, it allows the tube to be greatly shortened, making the design far more compact.  Similarly, because the secondaary is convex, it pushes light even further out of the back of the scope, meaning that longer focal lengths can be created with even shorter tube designs.   The net result is an OTA that's about 1/5th shorter than the focal length of the instrument; hence, the compact design.

We should be cautious about reflectors, however, since non-newtonian types of reflectors might do something different.  For example, a classical cassegrain, Ritchey-Chretien (RC), and Dall-Kirkham (DK) telescope, while being twice folded like a Schmidt or Maksukov (Mak) Cassegrain, are actually reflectors since they lack a lens element or corrector plate.   Interestingly, telescope-maker,  Planewave, markets their "CDK" , or "corrected Dall-Kirkham."  This design includes a pair of optical elements (lenses) just before the focal plane, making it a catadioptric design. 

Even more confounding, most any of the reflectors when used in imaging, especially RCs, will have optional field-flatteners/correctors sold as accessories, user-installed just before the focal plane.  Similarly, TeleVue produces their Paracorr, which is a correcting "eyepiece" that goes ahead of the typical eyepieces to correct the "coma" aberrations natural to a newtonian design.   What this goes to show is that the lines between the types of designs become very blurry in practical usage, since there is often a benefit to utilizing both lenses and mirrors as add-ons to traditional designs. 

Therefore, if you are confused by everything, then join the club!   

But rest assured none of that really matters right now, especially for the beginner.  However, since you've undoubtedly seen all the lingo in your research of prospective scopes, this discussion gives some context about what it all means.  

Refractors come in both achromatic and apochromatic designs.  This is necessary because refractive elements (lens) bend light differently at different frequencies.  You can see this with a typical prism, where light is spread out into a rainbow across its different frequencies.  As such, a telescope of a single lens element would be unable to focus all wavelengths at the same spot (a longitudinal error), meaning that red light (long waves) would be out of focus compared to the blue light (short waves).   Similarly, there is a component of lateral error as well, meaning that a lens cannot necessarily assure that all of a specific wavelength is focused on the same focal plane, since any distortion or magnification variance within the lens is wavelength specific as well.  

This, of course, is a problem...one in which mirrored scopes do NOT have...a big advantage with reflectors. 
​
The solution for this "chromaticism" within refractors is three-fold:  1.) use more elements, 2.) use elements of higher quality glass (extra-low dispersion or ED glass), and 3.) make the focal length long enough to increase the "zone of focus."  

An achromatic refractor, typically with two elements (made of low-cost crown and flint glasses), is designed to bring light to focus in two broad wavelengths, typically red and blue.  These "doublets" are easy to manufacture and are cost-effective, but they do not work to focus ALL the visible frequencies of light, most notably "violet."   As such, on bright objects like the moon and planets, purple fringing is typically seen on the edges.   This is called "spurious color" or "chromatic aberration."  This is even more obvious if they make the scope too short.  For this reason, many good achromatic doublets will be LONG, with f-ratios in excess of f/12 or f/15.   Longer scopes (high f-ratios) increase the critical zone of focus or depth of field (see image below), making it possible for all visible waves, albeit dispersed, to be contained within that focal zone.  Such scopes are good performers because they make best use of the design, working around its limitations.  

Problematic for the first time scope buyer are those doublets known as "rich-field" refractors, which are made at f-ratios of f/5 to f/8.  These, as you would expect, have abundant color fringing!   If used on dim targets like star clusters and Milky Way vistas (hence the term "rich-field"), then there isn't too much issue, but if you hope to use such a scope to get good views of planets and the moon, then you will likely be disappointed.  Likewise, if you bought the scope because of the "fast" f-ratios to do astrophotography, then you will be disappointed when most all the stars in the image, especially those at the edges of field, are a nightmarish purple mess.  

As mentioned, color performance can be improved in refractors by adding more elements of glass, which of course raises the material and design cost of the instrument.   This gives birth to the "triplet" refractor.  Such a design is typically "apochromatic," meaning that it will be able to bring three broad wavelengths of light to focus, typically red, green, and blue.  This should also bring "violet," and all other visible wavelengths, into focus as well.  Though it should NOT be reasoned that all triplets are inherently apochromatic.  Typically, true "apo" (or APO) performance requires the use of one or more of the elements being made of a special, extra-low dispension or ED glass.   FPL-53 is the typical "ED" glass found in most of these refractor types, so if you have seen it listed in the specifications for an instrument, then now you know what it does!  

In some cases, a doublet-design can also be apochromatic in performance.  Takahashi, in particular, once made a line of fine "fluorite" element doublet refractors (they still do in short production runs).  Fluorite, which is a remarkably low dispersion glass that is grown in a lab, is now in too short supply to make these refractors in abundance; however, such fluorite doublets are wonderful, high-contrast instrument without a hint of spurious color.   Takahashi also utilized fluorite in their triplets and quadruplets, which if you are lucky enough to have, are some of the best visual scopes on the planet.   To my knowledge, the small volume-maker, TEC, and Takahashi (in a couple of short-production run scopes) are the only companies that still makes APO refractors with fluorite elements.  

Be careful of doublet refractors being marketed as ED APO scopes.  A doublet with a single ED element of FPL-53 glass might not be truly apochromatic in the technical sense of the term, especially if the scope is on the "fast" side...let's say below f/7 or f/8.  These scopes, because of their performance value are very attractive to buyers since they advertise APO performance at a bargain price.  However, when compared side-by-side with a good APO triplet, it's easy to see that their color-fidelity is somewhat lacking.   Today, because of consumer blow-back by those who know better, many distributors of these mostly Chinese-made "value" scopes have backed off the "ED APO" branding, choosing to advertise these doublets as "just" ED scopes.   However, these scopes are a great middle ground, a good value option, particularly for those wanting a good photographic instrument and are willing to compromise just slightly on performance. 

To clarify another aspect of refractors, especially triplets, lens elements can be configured as either "air-spaced" or "oil-spaced."   In the air-spaced design, lenses are only separated by a thin amount of air between them.  This means light must pass through six surfaces before it exits the lens "cell."   Each time it passes through an optical surface, from the dense glass to low density air, there is the possibility of internal reflections that can create a slight ghosting effect as you get farther from the center optical axis.  This is fixed by using coatings on the surfaces of those elements, which most modern triplets do today.

But when the elements ARE spaced with oil in between them, then the oil fills the gaps, making it behave as if the light passes only through two surfaces, the front of the first and the rear of the last.  No need to use surface coatings, albeit it's much more difficult to assure both chromatic AND spherical aberrations are tamed.  

A good oil-spaced triplet is delight to use, high-contrast and very well corrected for aberrations, though it typically takes an advanced observer to appreciate it.  It also comes to thermal equilibrium very quickly!   An "oil-spaced" triplet is a rare breed today, since companies can get great performance in all aspects with the cheaper, air-spaced design. But companies like TEC still utilize the expensive "oil-spaced" design in their scopes.   Having used their TEC 140FL, TEC 180FL, and TEC 210FL models, which are also "fluorite" triplets, these are the very best views I've ever had through any telescope at their given apertures. 

Other oil-spaced triplets that I've used in the past include the William Optics FLT-110 f/6.5 and various Astro-Physics models.  Even today, for me, they represent some of the very BEST in optical triplet performance.   

Finally, another refractor design, also apochromatic, is the 4-element Petzval design.  It typically utilizes a color-correcting lens pair up front, with one-or-both elements of fluorite or FPL-53 glass, and an additional "field-flattening" pair of elements in the back of the scope.  Obviously expensive and wonderfully pristine in performance, it's typically the best refractor you can find if astroimaging is your desire.  The Takahashi FSQ-series of scopes utilizes this design, as does the TeleVue NP-series of APO Refractors.   Per inch of aperture, these scopes are the best optical instruments there is when you demand the best color-correction combined with the ultimate in field-flatness.   Both traits are highly desirable when imaging with today's larger sensors, so much so that most people purchase "field-flatteners" to be used with the already pristine doublet and triplet apos. 

Sidebar: Chinese Value Options

Americans often swell with pride when we see the "Made in the USA" label.  And maybe we should.  Companies like Celestron and Meade; boutique telescope-builders like Astro-Physics and Stellarvue and TEC and Planewave; and scope/eyepiece juggernaut, TeleVue, are all companies that originate right here in America.  

American pride must seem strange, or even narcissistic, to my non-American readers. They probably are better aware than we are that American companies outsource seemingly everything from overseas.   If it's not the whole product, then it's likely the assembly.  Apple iPhones are less "American" than Toyota pick-up trucks.        

It's those aspects of this hobby that lead to confusion...simply put, the majority of budget products (and even some pricey ones) that you are seeing in your online research from American companies are predominantly Chinese made.   

While there are indeed great astronomy items that are conceived, designed, and manufactured in the USA, those likely aren't the items that a newbie to the hobby is shopping for.   More importantly, for you the uninformed, you need to know how this hobby works; how it HAS worked for ages.   

Compare the following mounts from 5 major retailers... Each of these mounts is the EQ-3 type mount, produced in China by Taiwai-based Synta Corp.  All prices similarly in a base configuration, a touch of paint, labels, and perhaps the tripod are all that sets them apart.   Some companies might have found ways to add electronics to this mount, as Orion has in this picture, but the consumer has to know that they are essentially the same thing.  

Synta has produced these mount for ages (beginning in ), ranging from the EQ-1, which comes as the most basic of any company's cheapest telescope offerings, to the EQ-6, which is a hefty mount that can exceed the $ price tag in certain situations (it's a very configurable mount from an electronic aspect). 

Traditionally, the most popular has been the EQ-5 type of mount, that many people might know better as the Celestron AVX or Meade LX85.  Again depending on maker and the options if had, this is essentially the same mount...and almost all telescope retailers have a version priced somewhere in the $700 to $ range.  

In most cases, the origin of the mount can be identified within the model name for each company.  If you see CG-5, EQ-5, HEQ-5, or any mount with a 5, it's likely the same mount.  Same with alt-az mounts, AZ1, AZ2, AZ3, and AZ4...yep, all Synta. 

Of course, they make most of the OTAs as well.  If a company advertises a budget 70mm refractor, a 4.5" reflector (also known as the 114mm), all the way up in size...it's Synta.    Anything sold by Orion telescopes is Synta, and that includes the XT-series of Dobs and the 80ED and 100ED doublet ED/APO refractors.   Again, NOT everything "Synta" is bad.  Those refractors, which I criticized for the "ED/APO" label elsewhere in this Guide, I also praised for being a really good value performer.  And more than once in this Buyer's Guide I have recommended the Orion XT-8 dob as my "favorite recommendation" for a serious, beginning observer.   Oh, and the Skywatcher 8" Classic Dob is the same scope.  Compare below... Two of my favorite scopes to recommend to serious beginners are the Sky Watcher 80" Classic Dobsonian (on the left) and the Orion SkyQuest XT8 Classic Dob (on the right). Well, actually they are the same scope, with only a slight change to the rocker box. - Click to see bigger. Incidently, Synta isn't responsible for everything, nor is China.  Many American companies also source from Guan Sheng Optical (GSO) in Taiwai.   All those accessories like focusers, eyepieces, finderscopes, and adapters that come WITH all those telescope bundles?   That's GSO.    Oh, and how about all those Ritchey-Chretien (RC) tubes you see on Orion.  Heck, those are even labeled "GSO" in the model name. 

And any of the other items on those webpages you are surfing, like some of the 6" and 9" newts or the 93mm refractors...you have GSO to thank for that.    

Most people who've been in this hobby know this information.  Some are bothered by it; yet others like me celebrate it, because we know that such value options help grow the hobby that we love.   Now that YOU know it, use it....look for similarities in products, shop more specifically at an online dealer/distributor because you hear good things about the company or the "product line."  In essence, within the first $ in this hobby, much of what you see from a company is ALSO offered by somebody else...or many somebody's.   

There are USA-made scopes from Meade and Celestron, most notably the SCTs and Maks, the success on which those companies were built.  But to compete with retailers, Meade and Celestron are also forced to source many of the budget telescopes on their website; sales of which are responsible for the bulk of their income.

Don't be disappointed in this fact.  Instead, celebrate that open competition in these markets gives you many more choices at much lower prices.  While the choices are overwhelming sometimes, it's not a bad problem to have!