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High Quality Lenses from Knight Optical
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Lenses are used primarily to focus or diverge light, either as a single component or as part of a larger array. Convex lenses focus light to a point, whereas concave lenses diverge light away from the source. The focal length of any lens is dictated by its diameter, radius of curvature and the refractive index of the material. Simply put, materials with a high refractive index such as Germanium (n=4.0) or high index flint glasses  allow a lens to achieve a specific shorter focal length with a smaller diameter than the same lens made with a material of low refractive index. Materials also transmit in different wavelengths. Taking Germanium as an example again, UV and visible wavelength are blocked making the material appear opaque, but it allows IR transmission. This makes it undesirable for systems where UV or visible ranges are required. Conversely, our UV Grade Fused Silica lenses are excellent for ultraviolet applications achieving up to 85% transmission at 185nm.

Knight Optical offers a wide range of high quality lenses for a variety of applications, from aspheric lenses to correct spherical aberrations, to thin Fresnel lenses and large condenser lenses. We can supply from stock or bespoke, in a range of materials to suit and where necessary we can edge existing stock lenses for a fast turnaround.  Talk to our experienced, multilingual sales team for more information.

Aspheric lenses:  Aspheric lens surfaces are used to correct spherical aberration (where the converging light from a lens does not have a common focal point, resulting in a distorted image) in lasers and imaging. Traditional spherical lenses cannot collimate light effectively because even small angles of incidence can produce spherical aberrations. This can mean that several components may be required to get the desired result. The non-spherical surface of an aspheric lens allows a single component to effectively focus or collimate even highly divergent emissions, potentially replacing a multi-lens system with a single aspheric lens.  Knight Optical stock a range of aspheric lenses from Precision grade aspheric lenses providing excellent performance over the NIR and VIS spectrums. Plastic aspheric lenses which relatively cheap as they are mass produced moulded or pressed, plastic.
Fire-polished aspheric lenses which are ideal for light collecting applications as in projectors.  We have a huge tooling inventory available for custom aspheric lenses with “no tooling charges”
Aspheric lens sets  are available at reduced costs compared to individually priced lenses.
Diamond turned aspheric lenses  in a  range of infra-red materials is also available.

Ball & half ball lenses: most commonly used to couple light in and out of fibres. Knight Optical supplies a range of stock ball lenses as well as bespoke designs to your own specifications. Our stock ball lenses offered in quartz have excellent UV and IR transmission between 185nm to 2000+nm, while our sapphire lenses have a higher refractive index, allowing a very short fall back length to better facilitate fibre coupling. We can supply ball lenses in a range of alternative materials and diameters.  We are able to supply high precision grade 3 ball lenses, mid-range grade 25 ball lenses and commercial grade 100 ball lenses offering all grades to suit any application.  Aside from fibre coupling applications, ball lenses are also used as objective lenses in endoscopy, laser measurement systems and bar-code scanning.  Our range of half ball lenses offer uniform dispersion of light and are typically used in LED displays and LED traffic lights.

Drum & half drums lenses: Drum lenses and half drum lenses are adapted ball lenses.  The two spherical lens shapes either ends of the drum lens are still perfect for fibre-coupling and endoscopy applications. A half drum lens is manufactured by taking a full drum lens that has two spherical faces and then polishing one of its spherical faces to a plano flat face resulting in an elongated planoconvex lens.

Biconvex lenses: are a simple lens comprising two convex spherical surfaces, generally with the same radius of curvature. Knight Optical supplies a wide range of stock and bespoke biconvex lenses, available coated or uncoated.  Our range is available in BK7 and SF11 for visible and NIR applications, we also stock a range of UV fused silica type which work down to 175nm in the deep UV. Our biconvex lenses can be bought as single lenses or convenient lens sets.  Biconvex lenses have a broad range of applications including, but not limited to, focussing and control of laser beams, moderate quality imaging and other optical instruments.

Planoconcave and biconcave lenses: are a simple lens with one spherical face and one flat Plano face are simple lenses with one spherical face and one flat plano face or as in biconcave form having two concave faces. Because the spherical face is concave the lens has a negative focal length, allowing them to increase the divergence of convergent light.  Concave lenses can be used to balance out the spherical aberrations caused by other lenses.  This makes concave lenses very useful for controlling laser beams.  We stock a range of concave lenses from commercial grade though to high quality N-BK7 and UV Fused Silica types for deep UV applications down to 175nm and concave lenses made using high-index SF11, also including a range of high-index laser type.  We also stock a range of concave lens sets for design and laboratory use. 

Condenser lenses:  are plano-convex lenses used to project light into a concentrated beam and are effective at reducing spherical aberration.  As such, the primary purpose of a condenser lens is to provide high power illumination. This covers a broad range of applications lighting microscope slides up to car headlights.  Knight Optical supply a broad range of stock and bespoke condenser lenses for a variety of applications.  Our high quality lenses can be AR coated to improve.  We stock a full range of condenser lenses from fire-polished grade to large diameter plano-convex type from 114mm to 250mm diameter.

Cylindrical lenses:  Cylindrical lenses are designed to focus light into a straight line, rather than to a single point.  As the name suggests, the lens surface has a cylindrical shape rather than the usual spherical which allows for one dimensional shaping of light along a line.  Cylindrical lenses are typically either plano-concave or plano-convex, designed to expand and focus light respectively, and can be supplied in either diameter or rectangular shape for ease of mounting.are often used to change the profile of laser beams, for example to correct for astigmatism and ellipticity in diode lasers or to generate lines form single mode lasers. We offer a range of stock cylindrical lenses to suit a variety of applications.  Our quality BK7 range is used in visible and NIR applications where as our UV fused silica range is used in UV applications down to 175nm.  All our lenses can be AR coated for NIR transmission, typically between 450-900nm and alternative coatings are available on request.

Achromatic doublet lenses  A single lens used to form an image will always show some chromatic aberration, that is variation of focal length with wavelength.  Achromatic doublet lenses correct for this as they are constructed from two different glass types and designed to remove first order chromatic aberration. Generally spherical aberration is reduced at the same time.  Achromatic doublets are probably the most economical way of achieving quality white light illumination and imaging.  We stock a range of doublet lenses in various forms and quality from small 3mm dia up to 110mm dia to meet a range of demanding applications.  These stock lenses can be edged down at short notice to meet your specific custom requirement.
Quality achromatic doublet lenses   are widely used to form images, for example telescope objectives, and also to focus laser beams. Our range of quality achromats have been designed and optimised for performance and are available as positive and negative focal length types. Typical applications where achromatic doublet lenses are used are imaging, analysers, fibre-optic lighting, laser range finders endoscopes and borescopes. 
Commercial doublet lenses   are largely similar to the quality doublet lenses but not made to such stringent tolerances.  They are used for more general-purpose applications not requiring high quality, such as experimental and educational demonstrations.
Cylindrical doublet lenses  are used to focus light in one direction but at the same time reducing chromatic aberration which ordinary singlet type cylindrical lenses don’t achieve. Typical applications for cylindrical achromatic doublet lenses are changing the profile of laser beams, for example to correct for astigmatism and ellipticity in diode lasers or to generate lines form single mode lasers and focusing a beam onto linear detector arrays.
Achromatic doublet lens sets are available in a range of sizes for ease of use in a laboratory and design environments.  Doublet lens sets are more economical to buy compared to buying as individual lenses. 

Fresnel lenses: Fresnel lenses consist of a flat surface with interspaced, concentric steps whereby each step corresponds to the surface of a conventional lens.  Each step thereby acts as a refractive surface, much like a prism.  This gives the Fresnel lens a common focal length equivalent to a traditional lens, but with a fraction of the thickness.  Knight Optical offers a range of stock Fresnel Lenses made from PMMA Acrylic.  Our stock range of PMMA Fresnel Lenses comes in two grades. Our “standard range” start from 5mm f.l x 5mm diameter aperture up to 254mm f.l x 152mm dia aperture.  Our precision range has tight tolerances with improved surface quality and come in large aperture sizes.  Our Precision Range of Fresnel Lenses start at 22.2mm f.l x 44.4mm aperture up to 600mm f.l x 600mm dia aperture.  Fresnel PMMA lenses are ideal for simulators and projection systems.  We also stock a small range of cylindrical Fresnel Lenses.

Meniscus lenses: have one concave and one convex surface. In this lens type the two curvatures are chosen to minimise the spherical aberration at one laser wavelength, hence they can be useful to control a laser beam of the appropriate wavelength.  We stock two grads of meniscus lenses.Our high quality laser grade made from high index material and coated with AR coating for increased performance.  Our general purpose grade which utilise ophthalmic lens blanks offering low cost solutions.  The range has a wide selection of powers and is available in positive and negative options. 
We also stock a range of meniscus lens set for convenience of experimental and design work.

Planoconvex lenses:  have one plane and one convex surface and have a positive focal length.  Planoconvex lenses are typically used for focusing or collecting light in optical systems. Knight Optical stock a range of plano-convex lenses available from 2.5mm dia up to 100mm dia in a full range of focal lengths and materials to meet most applications.  Stock planoconvex lenses are offered as uncoated and antireflective coated ranges for increased performance from UV to NIR wavelengths.  A range of telecom 1700nm AR coated lenses are soon to be introduced.

Planoconvex lenses form a moderate quality image close to the axis.  They are generally used as elements within a more complex lens system or optical instrument in imaging systems, lasers and detectors.  Our stock range of planoconvex lenses consist of:
Quality BK7/SF11 planoconvex lenses  Plano-convex lenses are normally made of a medium index crown glass such as BK7 or BaK4 however for lower spherical aberrations lenses high index glass is used typically SF11.  These BK7/SF11 planoconvex lenses are available uncoated or AR coated for extended visible and NIR wavelength applications. 
UV fused silica planoconvex lenses  Synthetic Fused Silica Fused is an excellent choice of material for deep ultra-violet spectral range applications.  UV Grade Fused Silica has exceptional chemical purity, excellent thermal properties with low fluorescence making an ideal choice for medical fluorescence applications.  Our stock range of planoconvex UV Grade Fused Silica lenses are available uncoated or antireflective coated on both faces with multilayer AR for 248-400nm use.  However UV Grade Fused Silica can be used efficiently at 185nm transmitting over 85%.
SF11 high index laser lenses can have very little aberrations for a monochromatic on axis object. This makes them ideal for focussing laser beams. Generally they are cheaper than achromatic doublets but do not perform quite as well. The higher index gives them a greater residual surface reflection unless they are AR coated. 
Planoconvex lens sets Our ranges of planoconvex lenses are also available as convenient lens sets.
Our lens sets cover multiple focal length ranges and are very convenient for laboratory and research work. 

Plastic lenses: Most of the single lens forms, planoconvex, planoconcave, meniscus and aspheric, are available in plastic. Plastic lenses are generally cheaper and lighter than glass equivalents but of lower quality. Plastic lenses are not as robust as glass as they can scratch more easily and some will deteriorate when exposed to UV light.  If they are to be used outside the visible, in the UV or near IR regions, then their transmission must be checked.  Plastic lenses are typically used in low cost collimators, torches and lighting applications.

Rod & cone lenses: Knight Optical supply a range of rod and cone lenses for a variety of applications.
Cone lenses are cylindrical rod lenses with one end worked into a conical surface. The circumference of the rod is typically ground whereas the conical element is polished.  This makes the lens ideal for 360⁰ illumination, laser and imaging systems.
Plain rod lenses  are a special variant of cylindrical lenses in that they are complete rods where the light passes through the sides of the rod and focuses a line.  Rod lenses have an outside face that is polished and the ends ground.  The table below gives angular lengths of the line for a 1mm diameter laser beam. Typical uses for rod lenses would be to generate a line image from a circular laser beam.  We supply rod lenses both mounted and unmounted. Our mounted rod lenses can be easily attached to laser heads and then easily rotated into the correct orientation.   Supplied in borosilicate to meet visible and NIR applications.  We are able to manufacture a range of rod lenses from UV grade fused silica for applications working in the ultra-violet down to 185nm.  Rod lenses can also be polished on both ends and used as light pipe homogenising rods.
Graded index lenses  Grin lenses are used for laser diode beam shaping and optical fibre coupling or for image focusing of laser light onto detectors.  The interesting feature of a graded grin lens is that the material has a constantly changing refractive index through the lens.   Graded index rod lenses can be polished on both ends and cemented to the fibre light source.

Mounted Lenses and Lens Systems:  are  currently manufactured to custom specification.  Utilising our resources Knight Optical work with you, our client, to ensure the lens systems are fit for purpose.  Typical mounted lenses that we have produced for clients are:

  • Achromatic relay lenses with magnification ranges from about 1:1 to about 10:1.
  • Focussing / collimating lens assemblies from about 3mm to over 70mm in diameter. 
  • UV condenser lens assemblies from about 150mm and less in diameter.
  • Projector lenses: from about 100mm to less than 20mm in diameter. 
  • Microscope Objectives and Eyepieces such as plan achromats, plan fluorite, oil immersion, long working distance, and infinity corrected.  Huygenian and wide field eyepieces.
  • Microscope tubes with standard threads and 160mm length to make-your-own microscope. 
  • Telescopes and Collimators using lenses and / mirror from 50mm to 150mmdiameter for lenses and 100mm to over 300mmdiameter for mirrors.
  • Laser beam expanders from 5mm to 100mm in diameter, with fixed ratios of 2:1 to 10:1 at fixed laser wavelengths.
  • Zoom Laser beam expanders with ratios of 2:1 to 6:1 at fixed laser wavelengths with beam diameters from 5mm to 50mm. 
  • Loupes with fixed magnifications of 2 to 15. and long working distances.

Magnifiers: usually have a magnification range of 2 to 10, although the most common magnification is six times.  The magnifiers are made with a wide field of view and long eye relief that improves the ease of use.  The field of view commonly asked for has a diameter of about 40mm with a working distance of about 25mm.  The magnifier has a stand-off guide to keep the working distance constant.  This stand-off guide is transparent to allow light to illuminate the sample at the working distance.  These magnifiers have little aberration, such a pin-cushion or barrel distortion.  The observed field has a nearly constant illumination across the diameter of the sample.  The image is often asked to be a clear as possible.  The magnifier is designed to be optimum for the customers’ requirements.

Ophthalmic lenses: are available with powers ranging from -6 to +6 dioptres and with several base powers.  Generally ophthalmic lenses are used for spectacles/ reading glasses, however due to modern technologies these lenses are relatively cheap to produce and the quality good enough to use in scientific instrument applications.

Lens arrays and micro lenses:  The arrays, two off made from glass, are used to create, for example, an even illumination from a light source.  The arrays are monolithic that have a higher transmission and superior stability compared to cemented and plastic types.  Wavefront detection and measurement can be accomplished by using lens arrays with an array detector, such as a CCD.  Each lens focusses onto a small array that is a sub-section of the CCD and deduces the angle of the wavefront at the lens centre by which element of the sub-section the beam has its centre.  By making a set of readings over the entire lens array, and each sub-section of CCD detectors, the wavefront of the beam can be deduced.  This measurement is made at each frame rate and is therefore very fast. Micro-lenses generally have a diameter less than 1mm.  The lenses can by spherical, aspheric, cylindrical, and plane with positive power.  They are used, for example, to couple light to optical fibres.  These lenses are usually arranged in, for example, a square array.  These micro-lens arrays are used, for example, to increase the light collection efficiency of detector arrays,, for example, CCD arrays.  The micro-lens arrays have, for example. Been developed to form very small and compact imaging sensors for applications ranging from copiers to mobile phone cameras.

Triplet lenses:  take many forms, but the lens that is immediately thought of is the Cooke triplet.  This lens is, usually, achromatic and is considered to be a primitive design, which means, for example, most camera lenses evolved from it.  The three air-spaced elements permit flexibility in aberration control by not having the same radii as a cemented triplet requires.

Other forms of triplets are used for imaging the focal point of to another, such as in a periscope.  The cemented triplets are termed Steinheil, and Hastings.  The Steinheil has low refractive index centre element with identical high refractive index for the outer lenses.  They make use of symmetry to correct for aberrations, such as spherical, and are designed for 1:1 conjugate ratios.  The Hastings triplet is, for example, used as a magnifier lens.  It is corrected for distortion (pin cushion), chromatic, and spherical aberrations.

Contact our multilingual technical sales team and discover how Knight Optical’s high quality lenses can improve your product and supply chain experience.

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