effective diameter formula lens

IOT invites patients everywhereand the ophthalmic industryto embrace the light with Neochromes Agile Dark, the newest addition to the Neochromes family of light activated lenses. 0000016106 00000 n 1 Answer. ELP is defined as the effective distance between the anterior surface of the cornea and the lens plane if the lens was infinitely thin.4,5The ELP is considered to be the main limiting factor for refractive predictability after cataract surgery, as the accuracy of AL and corneal power measurements has been widelydemonstrated.7Improvements in IOL power calculations over the past 30 years are the result of improved predictability of the ELP variable. Nemeth J, Fekete O, Pesztenlehrer N. Optical and ultrasound measurement of axial length and anterior chamber depth for intraocular lens power calculation. The focal length - The focal length of a lens is the distance between its optical center and its focal point or focus. An improved universal theoretical formula for intraocular lens power prediction. The effective diameter of the lens is actually the cutoff value; the parts of the lens outside that distance aren't doing anything for us. It is important to use the effective diameter rather than the widest point or longest axis. where is the focal length, and is the diameter of the entrance pupil (effective aperture).It is customary to write f-numbers preceded by "f /", which forms a mathematical expression of the entrance pupil diameter in terms of and N.For example, if a lens's focal length were 10 mm and its entrance pupil diameter were 5 mm, the f-number would be 2. . Although the magnitude is correct, according to this . Clinical results using the Holladay 2 intraocular lens power formula. 0000006878 00000 n . You can measure the longest diameter but it is not the Effective Diameter (ED) that your lab requests. Refraction is the means by which light is deviated by a certain amount when it enters or leaves a medium. Haigis (a0, a1, a2optimized): short long eyes20,*, The Hoffer Q formula relies on a personalized ACD, AL and corneal curvature. Copyright 2023 IcareLabs. 0000003981 00000 n Dont see what you need? You can change this selection at any time, but products in your cart, saved lists, or quote may be removed if they are unavailable in the new shipping country/region. Furthermore the parameters of each formula used for the ELP prediction are listed as well as recommendations of formulas for different eye types according to various sources. Biometry and formula accuracy with intraocular lenses used for cataract surgery in extreme hyperopia. Field of View (FOV) = 90mm. Base Curve = The curve from which all other curves are measured. The effective diameter is the inside diameter of the objective lens frame. MSU is directly affected by the amount of decentration. Another way to calculate the FRAME PD is to find the distance between the GC of each lens. NRP = Near Reference Point, reference point for best visual acuity for near vision. Thanks for contributing an answer to Physics Stack Exchange! As with other constants the surgeon factor is not actually a measurement, but a number representing a particular surgeon's previous experience.23, The Holladay 1 is recommended for eyes measuring between 24.6 mm 26.0 mm.22. *The more shallow curve on the backside of a lens is the called the toric curve. n: refractive index of observation medium [e.g. A table of such constants, which we will call thickness factors, can be prepared and kept readily available. The answer is thickness. (Always add 2mm to allow for blishes on the edge of the lens) It is important to use the effective diameter rather than the 'widest point' or 'longest axis'. Of these characteristics, resolution is . Ophthalmology 1998; 105: 1759-64. OC = Optical Center of Lens (that point on a lens through which a passing ray is not deviated). Warning: the effective aperture diameter is not necessarily the same as the diameter of the part of the front lens element in use. Comprised of two inward, equally curved surfaces. IOL Power Calculations Which Formula? To learn more about telecentric lenses, view The Advantages of Telecentricity. Relation with focal length: A lens of less focal length produces more converging or diverging and is said to have more power. ED = Effective Diameter (longest diameter of lens) DBL = Distance between Lenses. To understand the terminology used in optical lens specifications, consider 10 common terms (Table 1). Thorofare, NJ, USA: Slack Incorporated, 2004. f/# of a simple lens is defined by the following equation, where f is the focal length of the lens and D is the diameter (or more specifically the entrance pupil diameter for more complex lens systems). Image from Laramy K (Optician Works) Thank you John Seegers. The aperture of the lens is the effective diameter of its light-transmitting area. (2) Normal Module System Worm Gear Pair. Selecting the right lens blanks can avoid many headaches for optical dispensers. It is given as, 1 i + 1 o = 1 f. i= distance of the image from the lens. Back Focal Length A mechanical measurement given as the distance between the last surface of an optical lens to its image plane. This deviation is a function of the index of refraction of the medium and the angle the light makes with respect to the surface normal. Only based on the photo I should calculate the diameter of the lense. Holladay JT, Prager TC, Chandler TY, Musgrove KH, Lewis JW, Ruiz RS. To get each eye separately, divide your answer by TWO. As most of us know, in this industry, being off by even just a millimeter can be the difference between a happy patient and a frustrated patient that could leave your business a bad review. 1993 Nov;19(6):713-20. Provides best VA when line of sight is lined up with the OC. Figure 1. This results in higher resolution and a brighter image. Beam Quality Factor. 1993 Nov;19(6):713-20. A - EYE SIZE - The horizontal width between the two vertical lines tangent to the edges of a lensor a box enclosing the lens. As mentioned above, we just need to multiply 27mm by 2 which gives us the correct ED . Lenses are manufactured with a limited number of standard focal lengths. The same method can be used from a dotted pupil centre. to the edges of the lensor a box enclosing the lens. but calculates them automatically by the following formula: 114.6 * arctan (21.622 / CF * FL), where: CF - crop-factor of a sensor, FL - focal length of a lens. Hundreds of stock aspheric lenses ready for purchase, available in glass, plastic, or infrared crystalline material. When planning cataract surgery, one of the most crucial stages for treatment success is choosing the correct intraocular lens (IOL) power.1To reach the targeted refraction, the selection must be performed according to the anatomical and optical parameters of the eye.2In most cases, the target refraction is emmetropia but in some cases, depending on the specific needs and demands of the individual patient, other targets might be required, such as leaving some level of residual myopia in one eye (monovision).3One of the most important parameters in IOL calculation, particularly in non-syndromic myopia, is axial length (AL). Note: A smaller apex angle generates a larger ring. Using this example, the green line measures 27mm. Can Martian regolith be easily melted with microwaves? In the second part of his special series, LEIGH ROBINSON explains how to get measurements right every time. The effective diameter is the inside diameter of the objective lens frame. Jillian Campbell takes reins at Richard Lindsay & Associates, Vale Christine Craigie, a passionate and tireless supporter, Glaukos submits FDA application for iDose TR glaucoma implant, New FACE FACE collection draws inspiration from 1980s artistic movement, Ian Brigden in Nelson Bay joins George & Matilda Eyecare, Optometry Australia president Murray Smith resigns; state divisions signal reform, Siblings treated with Luxturna gene therapy in Australian first (video included), Victorian optometrists to administer COVID-19 vaccines, Delta disruption: O=MEGA21 cancelled, Eyecare Plus conference postponed, Oculo acquired by Finnish ophthalmic device company, Fair Work reaches decision on legal saga that threatened optometry salaries, Long wait finally over for Melbourne optometrists, Melbourne elective surgery limited to most urgent cases, Medical students fear for jobs as internship crisis looms, (The lens is decentred IN, because the PD is smaller than the frame), Decentration =FCD / 2 Mono PD, MSU = FCD PD + EFFECTIVE DIAMETER (ED), (Always add 2mm to allow for blishes on the edge of the lens). Insight has been the leading industry publication in Australia for more than 40 years. Changes in corneal power can alter the IOL power in a ratio of nearly 1:1. A three-part system for refining intraocular lens power calculations. Fourth generation formulas, like the Barrett, Haigis or Holladay 2 formula, have the advantage of including the non-proportional relationship between the ACD and AL and therefore should provide the highest accuracy over the full range of ALs. B EYE HEIGHT - The vertical height between the two horizontal lines tangent Looking for an opportunity to expand your career? 0000001857 00000 n So, using this equation, we can figure that if working at a 1:1 (1.0x) magnification at f/4, your effective aperture will then be about f/8 . You can also utilize our frame shape numbers when placing your orders on our myIcareLabs customer portal. Written on the barrel of your lens, or digitally inside your camera and displayed in the viewfinder or LCD screen, you probably see f/stop markings at one-stop increments.Oct 28, 2018. The cornea and lens of an eye act together to form a real image on the light-sensing retina, which has its densest concentration of receptors in the fovea and a blind spot over the optic nerve. Snell's Law describes the relationship between the angles of incidence and transmission when a ray travels between multiple media (Figure 2). Box Measurement Definitions and Additional Verbiage to help with following formulas. Does a summoned creature play immediately after being summoned by a ready action? It only takes a minute to sign up. However, large-diameter objective lenses make binoculars bigger and heavier. When optical designers talk about optical lenses, they are either referring to a single lens element or an assembly of lens elements (Figure 1). (Factorization), Identify those arcade games from a 1983 Brazilian music video. Negative version also available. Which formula to use for which eye (length)? J Cataract Refract Surg. Development of the SRK/T intraocular lens implant power calculation formula. The formula used to assign a number to the lens opening is: f/stop = focal length / diameter of effective aperture (entrance pupil) of the lens. The effective diameter of the circular outline of a spherical . The only parameter that cannot be measured preoperatively is the position where the IOL "settles down" after surgery, which is also known as the effective lens position (ELP). $ \small{\text{CT, CT}_1, \text{CT}_2} $, etc. By centai in forum General Optics and Eyecare Discussion Forum, By peyes in forum General Optics and Eyecare Discussion Forum, By cnet_baby in forum General Optics and Eyecare Discussion Forum, By Borysko in forum General Optics and Eyecare Discussion Forum, By au in forum Progressive Lens Discussion Forum, General Optics and Eyecare Discussion Forum, http://www.eyeglasslenses.com/contenasurements.asp, Professional and Educational Organizations, Professional and Educational Organizations Discussion Forum. The top and bottom lines provide you with your A measurement of 51mm while the 2 vertical lines provide your B measurement of 35mm. The best answers are voted up and rise to the top, Not the answer you're looking for? 0000111999 00000 n I won't link to it here, but even the top snippet on Google incorrectly states the LD as the ED! The ED is essentially the minimum lens diameter that will completely encompass the frame, in the absence of decentration. The focal length is the distance between the optical centre and the focal point or focus of the . The power of the lens of an eye is adjustable to provide an image on the . Airy Disc Diameter: [tex]D=2.44**f_{number}[/tex] Where: D = Diameter to first intensity zero (microns) You're simply creating a box around the outside of the frame by making 2 horizontal lines at the top and bottom of the frame. These are AL, corneal power, ACD, lens thickness (optional), age (optional), white to-white corneal diameter (optional), pre-operative refraction data (optional). Intraocular lens power calculations. N.A. Don't worry, if you are sending a frame to the lab for lenses, they will trace the frame and measure the effective diameter directly. The point source is blurred and has a size of 3.5 cm on the ruler. = n * sin . The lens power is measured for different positions of the source. The Royal College of Ophthalmologists Cataract Surgery Guidelines September 2010 Scientific Department The Royal College of Ophthalmologists. Spot Size Calculator. When we hear decentration we are usually speaking of a lens being decentered horizontally. When the wearers PD is smaller than the FCD, which is common, the lens must be decentred in, towards the bridge (Fig 2). Hoffer KJ. (nasally because the patients pd is more narrow than the frame PD), Example for vertical decentration, if the OC is 48 and the SEG HT is 22 then. To determine decentration here, we halve the FCD. Solving for x yields -2, which means that the image is inverted. Knowing the advantages and disadvantages of each lens type is crucial when choosing between optics as each has its own purpose. $\begingroup$ If I add the formula you gave for delta to the formula for BFD, f2*(f1-d)/(f1+f2-d), it does not appear to equal the formula for effective focal length. This allows all three constants to be optimized for a wide range of ALs and ACDs using double-regression analysis. For example, for a lens decentred by 4mm the blank will need to be 8mm larger. Another easy way to get the correct ED measurement is to let your edger do it for you. Not all products, uses, treatment options, and protocols referenced are officially approved or supported by a products intended use in every market. Frame: Eyesize 46, R: +2.50DS / +2.50DC x 180 with 2 prisms up and 3 prisms out, General Optics and Eyecare Discussion Forum, Professional and Educational Organizations, Professional and Educational Organizations Discussion Forum, The Spectacle Lens Group Of J&J, Inc. J CATARACT REFRACT SURG-VOL 14, JANUARY 1988. It includes (1) a factor that increases the ACD with increasing AL, (2) a factor that increases the ACD with increasing corneal curvature, (3) a factor that moderates the change in ACD for extremely long and short eyes, and (4) a constant added to the ACD.21, The Hoffer Q formula should be used for eyes measuring < 22 mm, according to the Royal College of Ophthalmology guidelines.22, The Holladay 1 formula uses the postoperative stabilized refraction value, the dioptric power of the implanted IOL, and the preoperative corneal and AL measurements to calculate a personalized surgeon factor. In conclusion, calculation of the IOL power can be performed using a great variety of formulas. AL, corneal power, ACD (optional), lens thickness (optional), white-to-white corneal diameter (optional). An improved universal theoretical formula for intraocular lens power prediction. More than just an app Consider the thick bi-convex lens shown in Figure 2.5.8. 1 R 1 1 R 2. This is important because many lens designs may not have a size available that fit the patients frame choice. Making statements based on opinion; back them up with references or personal experience. n (air) = 1] : angle between the optical axis and the light at the outermost of the effective diameter of the lens. But why not just use the biggest lens possible? The difference is 10. The beam diameter is defined as the distance between the points opposite to the diameter of the beam diameter surface, where the power per unit area of the beam is 1/e (0.368) times the displacement power per unit area. DRP = Distance Reference Point (should be slightly higher than the fitting cross (based on progressive lens design). Lenses and frames combine to make spectacles, so we need to be in control of the order from the beginning. From here we can get the correct ED measurement. From here we can get the correct ED measurement. Note: Aberrations will increase as the conjugate ratios increase. . One of the most important frame measurements is the ED, yet we consistently see this has the most confusion on how to get the correct measurement. What we are trying to find out here is what is the smallest lens that can be used that can fit into the frame that was selected. Download scientific diagram | Formulas used for calculation of effective diameter. This focal range increase naturally affects the angle of view because the longer the focal length, the narrower the angle. Entrance Beam Diameter Diameter of collimated light entering an axicon. Privacy Policy. Most of them use paraxial optic formula (Gaussian equation, Newton equation,) Others use can someone please explain and show how this can be done because all the equations are confusing. HOW TO MEASURE A FRAME Now that we have briefly explained what numerical aperture is, we can equate it to f/#. focal length calculator. Barrett GD. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The Thin Lens Equation for Gaussian Beams. J CATARACT REFRACT SURG-VOL 16, MAY 1990. 0000004020 00000 n The steeper curve is called the cross curve, - Powers: 1/2 Spherical Equivalent +6.00 D. This is not a common lens focal length so either the working distance would need to be adjusted or a non-standard lens that allows the user to vary the focal length is required. 0000082517 00000 n Did any DOS compatibility layers exist for any UNIX-like systems before DOS started to become outmoded? This results in higher resolution and a brighter image. HtUKs6WX4 863 h 0000009852 00000 n It is -0.005 not 0.005 because the lens moved away from the eye (follow the rule above)-0.005 X 18.00 . Predictions of ACD, which increases relative to the increase of AL, are based on initial and generally large datasets from which the formulas have been derived; however individual ACD measurements were not included in the prediction model. ED Effective Diameter; twice the longest radius from the geometric center of lens to the farthest edge; the smallest circle that will completely enclose the lens. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. This is the definition of the beam diameter and is used to calculate the maximum allowable exposure of the laser beam. ED - Effective Diameter; twice the longest radius from the geometric center of lens to the farthest edge; the smallest circle that will completely enclose the lens. The aperture of the lens is the effective diameter of its light-transmitting area. 0000001836 00000 n Product specifications are subject to change in design and scope of delivery as a result of ongoing technical development. Approved labeling and instructions may vary from one country to another. The effective diameter of the frame helps us to determine the MSU: the absolute minimum stock lens to be fitted to the desired frame within prism tolerance (Australian standards, AS/NZS ISO 21987: 2011). Also known as biconcave lenses. The aperture of a telescope then will simply be listed as the diameter of the main lens in millimeters, inches, or both. While this number may be close, it is not correct and can wreak havoc on making the patient's glasses right the first go around. The Haigis formula therefore uses three measurements, AL, K and pre-operative ACD with the three IOL constants a0, a1 and a2.12Olsen's formula is based on two additional measurements - pre-operative refraction and lens thickness - and delivers one IOL constant whereas the Holladay 2 formula is based on seven measurements, including the patient's age and the horizontal WTW measurement.1,5Finally, the Barrett formula uses a theoretical model eye whereby ACD is related to AL and K, and is also determined by the relationship between the A-constant and a lens factor'. Before delving into each type of lens geometry, consider how optical lenses bend light using the property of refraction. ED = Effective Diameter (longest diameter of lens), DBC/GCD (Distance between GC/ Geometric Center Distance) = Distance between centers of each lens (frame PD), Datum Line = Line that runs horizontally through the GC of the lens. Length The physical distance from end to end of a cylindrical element (e.g. This is a code assigned to all external communications materials, to assist in tracking and monitoring during the internal approval process. Given the same magnification, the larger the objective diameter, the greater the light-collecting power. Intraocular lenses (IOLs) and OVD portfolio, Optical coherence tomography (OCT) systems, Phacoemulsification, Vitrectomy and Lens fragmentation devices. The Haigis formula recommends an IOL power based on a three-variable (a0, a1and a2) function. Connect and share knowledge within a single location that is structured and easy to search. To learn more, see our tips on writing great answers. The Hoffer Q formula: A comparison of theoretic and regression formulas Kenneth J. Hoffer, M.D. Explore our integrated Workflows per Specialty. J Refract Surg 2009; 25: 229-34. It looks like this. Table 2 shows 10 of the most commonly used optical lenses and their typical applications. Binoculars are classified according to the effective objective lens diameter as follows. These are the AL, corneal power, ACD, lens thickness, age, white-to-white corneal diameter and pre-operative refraction data. Means the diameter is the focal length divided by 4.0. + 2 = 65mm Minimum Blank Size. Section 2: The Lens Equation 6 2. The intensity of the image formed by the lens also depends on the distance of the image . For minus-powered lenses, the maximum thickness occurs at the edge of the lens, so excess . J Cataract Refract Surg 2003; 29(1):85-8. The effective diameter and its angular location in a frame are also used in lens layout. (The OC and MRP are the same if there is no prescribed prism). Table 1. The Base Curve is on the front of the lens and is POSITIVE (+) in power. d = 2.44 * * f Where. Focal reducers are simply small mirrors or lenses with positive power that decrease the focal length. If this is your first visit, be sure to The critical refractive index value varies with the microsphere diameter and increases from ~1.84 to ~1.89 in the simulated diameter range. A photo produced with a single thin lense is provided. J Cataract Refract Surg 2010; 36: 1474-8. (0 members and 1 guests). an approximate formula: . where v is the image distance. Use MathJax to format equations. For additional information, view All About Aspheric Lenses. The Holladay 2 formula is conceptually based on the Holladay 1 formula; however it uses seven parameters for predicting the surgeon factor. Optimized with IRD, HaigisIRD formula achieved the lowest SD and had comparable accuracy with Kane formula. Hold the ruler over the frame front and sight an imaginary line from the farthest edge of a box touching the left temporal lens edge of the right eye to the right edge of the box. The Linear Diameter of the Airy Disk. Fenzl RE, Gills JP, Cherchio M. Refractive and visual outcome of hyperopic cataract cases operated on before and after implementation of the Holladay II formula. As well as AL and K, other parameters that may be also required, depending on the type of formula used, are the preoperative ACD5and the corneal white-to-white distance (WTW; also called the horizontal corneal diameter).6The anterior chamber is the fluid-filled space between the iris and the innermost surface of the cornea and the WTW distance is the horizontal distance between the borders of the corneal limbus. To solve an equation, one must find the value of the variable that makes the equation true. We've added a "Necessary cookies only" option to the cookie consent popup, How to Ray Trace Chief and Marginal Rays in Thin Lens Systems, Lensmaker's equation and Imaging properties. Empirical optimization methods of the SRK/T model primarily consist of (1) postoperative ACD prediction, (2), a retina thickness correction factor and (3) corneal refractive index.25, The SRK/T formula should be used for eyes > 26 mm. effective diameter ED of the frame and twice the required decentration (Dec), or MBS = ED +2Dec The effective diameter is twice the distance from the geometric center (GC) of the frame to the farthest point along the eyewire. These measurents are not always accurate and sometimes lead to disagreents between the lab and the practice. A three-part system for refining intraocular lens power calculations Jack T. Holladay, M. D. Thomas C. Prager, Ph.D. Thomas Y. Chandler, M. D. Kathryn H. Musgrove, M.D. Ideal for laser focusing or for replacing multiple spherical lens elements in a system. How can we prove that the supernatural or paranormal doesn't exist? any recommended book about frame adjustment and measure? The ED can also be defined as the smallest diameter lens that would cutout, if the frame's geometric center matched the lenses optical center. Material Processing Solutions & Robot Vision. Maximum diameter x Length: <No data> . We can solve this approximate equation for various values of the diameter and the refractive index in advance. I derived delta myself and arrived at the same formula you gave so I assume it's correct, but I can't figure out why adding delta to BFD doesn't yield the formula for EFL that I have found in numerous sources. For additional information, view Why Use an Achromatic Lens? Value. Comments Off on effective diameter formula lens; June 9, 2022; effective diameter formula lens Hb```f`` @Q9?e_:Qat]"T8P"uHyeQz-JLXzbbf[TNU'Vl2_PIIIg Decentration = 8. The most frequently used formulas are based on two measurements, AL and K, as well as a single IOL constant8(Holladay 1,9SRK/T10and Hoffer Q11). . Optical lenses are the most important tools in optical design for controlling light. 0000011628 00000 n This monster telescope took seven years to build, had a cost of $147 million . In a hypothetical example, let's assume the height of the original image is 8 cm. 0000008037 00000 n The modulation transfer function is a formula for determining the resolution curve of a lens, quantifying factors such as diffraction and aberrations. Acidity of alcohols and basicity of amines, Does there exist a square root of Euler-Lagrange equations of a field? As you zoom the lens in, the aperture opening as seen from the front appears to increase in size, just as predicted by the equation: absolute aperture = focal length / 2.8. Neochromes Agile Dark lenses are even darker than IOTs current Neochromes yet fade back just as quickly. That's the A dimension. A bigger plus lens will add more thickness to a lens, and lead to an unhappy customer. 0000006182 00000 n Optical lenses are the most important tools in optical design for controlling light. (0 members and 1 guests), By Jim Schafer in forum Smart Lens Technology by Transitions Optical, By Newsroom in forum Optical Industry News, By Eyeseeit in forum General Optics and Eyecare Discussion Forum. (ED) + 55. This effective diameter formula lens we have the second part of our look at the edge the. Shammas HJ. . 0000008059 00000 n The ED measurement is twice the distance of the farthest point from the geometric center as shown below: The green line above now indicates the ED for this frame. The Major Reference Point (MRP), the optical centre, frame measurements and the Effective Diameter (ED) are all important to getting it right, and avoiding a call from your lab about cut out. 0000002229 00000 n Be sure to consider the depth of the bevel when measuring the frame. 0000013879 00000 n DBL Bridge size; the minimum distance (nasal) between the two lenses or Lens Calculator. . Also known as biconvex lenses. Am J Ophthalmol 2007; 143: 920-31. http://www.doctor-hill.com/iol-main/formulas.htm Accessed 26 September 2016. The frame PD is calculated by adding the A measurement to the Bridge Measurement. check out the. 0000011161 00000 n hbspt.cta._relativeUrls=true;hbspt.cta.load(515393, 'b6d25137-5b44-4002-9e75-95c36d43cf85', {"useNewLoader":"true","region":"na1"}); In 2008 Camille joined IcareLabs and is currently serving as our customer service manager where she helps oversee our team of account managers and is an integral part of our success. Focus - The point at which collimated light parallel to the axis is concentrated is referred to as the focus. The value of the constant K to use in the above formula, for estimating the center thickness of a plus lens or edge thickness of a minus lens, is based upon the refractive index of the lens material. The personalized ACD (pACD) is developed from any given series of a particular IOL style. Information on Screw Threads. Copyright 2020, Edmund Optics Inc., 101 East Gloucester Pike, Barrington, NJ 08007-1380 USA, http://www.edmundoptics.com/knowledge-center/application-notes/optics/understanding-optical-lens-geometries/, Do Not Sell or Share My Personal Information, California Transparency in Supply Chains Act. J CATARACT REFRACT SURG-VOL 19, NOVEMBER 1993. There are currently 1 users browsing this thread. Lens diameter: As the size of the lens blank increases, the maximum lens thickness increases (rapidly)and vice versa. 0000012453 00000 n ED is used in combination with decentration distance to select the minimum lens blank . The lens formula is applicable to all situations with appropriate sign conventions. Examples of single elements are plano-convex (PCX) lenses, double-convex (DCX) lenses, aspheric lenses, etc; examples of assemblies of elements are telecentric imaging lenses, infinity-corrected objectives, beam expanders, etc.