This tutorial provides a brief introduction to the ISO 10110 optical drawing standard. The indications included on an ISO 10110 optical drawing are defined, and an example drawing is provided to illustrate how the information is commonly presented. To aid the designer who may not be familiar with the capabilities of optical shops, a set of specification values are provided, which illustrate easy, typical, and difficult values to achieve in fabrication. The same type of information is presented for lens dimensions. Finally, a set of design best practices are presented to aid in reducing fabrication difficulty and cost.
The ISO 10110 standard is an optical drawing standard used to explicitly describe an optical part based on the principle of geometric dimensioning and tolerancing (GD&T). Although the ISO 10110 optical drawing standard has begun to see widespread use in the optical industry, an optical shop will often receive an ISO 10110 drawing that is incomplete or incorrectly implemented. In talking to vendors and fellow designers about the issue, it became obvious to me that most errors arise from a designer’s or a design team’s unfamiliarity with the standard and how to implement it. This is not particularly the designer’s fault. The real problem seems to be the lack of a ‘simple, practical’ guide for generating an ISO drawing. In particular, a guide is written for designers who may want to use ISO 10110 but are unsure of where to begin or for anybody who may need a lens fabricated but is not necessarily familiar with the details of optical fabrication.
The goal of this tutorial is to fulfill this role as an aid to the designer or the drafter in adequately and correctly completing an ISO 10110 drawing.
2 Geometric dimensioning and tolerancing
ISO 10110 fundamentally relies on the principles of GD&T to describe a mechanical part. GD&T was devised as a method to explicitly describe nominal geometry and allowed variation for use in engineering drawings. In the United States, the use of ANSI Y14.5-2009 is almost universal, although many machine shops may still rely on ANSI Y14.5M-1994 because the current version is relatively new. Under the ISO system, geometrical product specifications (GPS) are governed by the Technical Committee (TC) 213 and include ISO 286-1 and -2:2010, ISO 1101:2012, ISO 5458:1998, ISO 5459:2011, and many other standards. GD&T standards for data exchange and integration are governed by ISO 10303. It would be a good idea for the designer to verify what revision of standard the fabricator uses when submitting drawing packages to avoid any possible misinterpretations .
This tutorial assumes that the reader is familiar with basic GD&T/GPS practices, so we can focus on the unique practices associated with describing optical components. As a mechanical part, an optical component can be described to some extent under the standards listed above . However, the unique aspects of optical components require additional standards to accurately describe the part to be made.
3 ISO system for specifying optical components
ISO TC 172, Optics and Optical Instruments, writes and maintains the majority of standards for specifying optical components. Under their cognizance, ISO 10110, Optics and Optical Instruments – Preparation of Optical Drawings for Optical Elements and Systems, is the primary reference for the preparation of drawings for optical elements and systems. ISO 9211, Optical Coatings, is also very important. In addition to these, there are many ancillary standards that contribute to the specification and testing of optical components. A complete list of ISO standards under the purview of TC 172 is available from the ISO website at http://www.iso.org.
4 ISO 10110 standard summary
ISO 10110 is a multipart standard describing the preparation of drawings for optical elements and systems. Table 1 lists the part numbers and the aspects that the parts cover.
|ISO 10110-2||Material imperfections – stress birefringence||0/|
|ISO 10110-3||Material imperfect – bubbles and inclusions||1/|
|ISO 10110-4||Material imperfections – inhomogeneity and striae||2/|
|ISO 10110-5||Surface form tolerances||3/|
|ISO 10110-6||Centering tolerances||4/|
|ISO 10110-7||Surface imperfection tolerances||5/ and 15/|
|ISO 10110-8||Surface texture|
|ISO 10110-9||Surface treatment and coating|
|ISO 10110-10||Table representing data of a lens element||N/A|
|ISO 10110-11||Nontolerance data||N/A|
|ISO 10110-12||Aspheric surfaces||N/A|
|ISO 10110-17||Laser irradiation damage threshold||6/|
Each part describes very well how to place each indication on the drawing and what the values mean. There are also a few examples to show what the indications should look like. I highly recommend that if you design lenses as a career, you obtain and maintain a set of the ISO 10110 standards and keep them near your desk as a reference. This is especially true if you work with optical shops in countries where the standard is widely adopted or if – as an optical shop – you receive bids that include ISO 10110 drawings in the bid package.
But let us be honest. Like any standard, ISO 10110 makes a great short-term cure for insomnia, and the learning curve is steep when, as a designer, you are unfamiliar with generating optical drawings or how an optical shop fabricates a lens. Additionally, an optical shop encountering an ISO 10110 drawing for the first time (such as what happens quite often in the United States) will be lost trying to interpret the drawing. Some optical design programs, such as ZEMAX or CODE V, include the option to generate ISO drawings and will even dimension the part. However, you still need to provide a large amount of information to correctly specify the lens. The first question you probably ask is this: What numbers do I put in?
5 Specification examples
One of the worst mistakes that a designer can make is to submit an incomplete drawing to a fabrication shop and ‘hope for the best’. You may get lucky the first time you try this approach, but at some point you will get a lens back that was not what you wanted. Of course, this will usually happen when you are behind schedule and your project manager is asking you for daily status updates. In other words, your part will fail at the worst possible time.
The second worst mistake you can make is to provide a drawing to the fabricator with tolerances and specifications so tight that it will be unnecessarily costly and threaten the schedule. You do not want to go back to the optical shop a few months later and find your drawing framed on their wall with the caption: ‘Our most difficult fabrication job yet!’ I am going to help you avoid this embarrassment.
Let us examine two useful tables that will aid in completing an ISO 10110 drawing [5, 6].
Table 2 is a set of specifications that I have developed to illustrate ISO 10110 indications. The table includes three sets of specifications that correlate to low-quality, typical, and high-quality lenses. Much of these specifications control the quality of the glass that the lens is made out of and thus are of immediate importance to the glass manufacturers. However, it is important to note that the indications apply to the finished lens.
|Parameter||Indication||Low quality||Typical||High quality|
|Stress birefringence||0/A||20 nm/cm||10 nm/cm||4 nm/cm|
|Surface irregularity (for spherical surfaces)||3/A(B)||3/-(2) (radius tolerance is a dimension)||3/3(0.5)||3/1(0.2)|
|Centering tolerances (wedge, arc minutes)||4/σ||4/5′||4/2′||4/0.6′|
|Surface imperfection (scratch and dig per MIL-PRF-13830 in the USA)||5/N×A; 5/LN″×A″; 5/EA′″||5/5×0.5; 5/L1×0.008; 5/E1.0 (80–50 in the USA)||5/5×0.4; 5/L1×0.006; 5/E0.5 (60–40 in the USA)||5/5×0.05; 5/L1×0.001; 5/E0.5 (10–5 in the USA)|
|Laser irradiation damage threshold||6/HTH; λ; pdg||6/10; 1064; 2 (group 2 per ISO 11254-1)||6/20; 1064; 2 (group 2 per ISO 11254-1)||6/40; 1064; 2 (group 2 per ISO 11254-1)|
Table 3 is a list of tolerances for fabrication and mounting of lenses. The ‘Easy’ column is a list of tolerances that, if loosened further, do not provide any significant reduction in the cost of the lens. The ‘Typical’ column is about what a typical shop expects to see, and tightening these tolerances much further will begin to significantly raise the cost of the lens. The ‘Difficult’ column really pushes the limits of what most optical shops can do, so expect tolerances such as these to result in significantly higher fabrication costs.
|Center thickness||±0.10 mm (0.004″)||±0.025 mm (0.001″)||±0.005 mm (±0.00025″)|
|Diameter||+0.00/-0.10 mm||+0.00/-0.025 mm||+0.00/-0.025 mm|
|Clear aperture||90% of diameter||94% of diameter||98% of diameter|
|Mounting decenter||±0.10 mm (0.004″)||±0.025 mm (0.001″)||±0.005 mm (±0.00025″)|
|Radius of curvature||1%||0.3% to 0.1%||0.05%|
|Coating||Average transmission >96%||Average transmission >98%||Minimum transmission >98%|
|Protective chamfer (levels)||0.75–1 mm||0.1–0.3 mm||0.02–0.1 mm|
As they say in the United States, ‘Your mileage may vary’, so I encourage you to work with your vendor and/or glass manufacturers to determine their specific capabilities and ensure you obtain the part you need at the best possible price point.
One final note on tolerancing: If a specification has not been toleranced, ISO 10110-11 provides a set of ‘default’ tolerances that scale with the size of the part. This is common in Europe but is a practice that opticians and engineers in the United States are not used to. Some of the default tolerances can be very loose and can lead to performance problems with the lens if a tolerance on the drawing is overlooked. I recommend that all specifications and dimensions be tolerance on the ISO 10110 drawing. If desired, a tolerance can be removed from the drawing if the ISO 10110-11 tolerances are acceptable. However, sending a drawing to a US optical shop without clearly defined tolerances may generate requests for clarification. The ISO 10110-11 default tolerances are provided in Table 4.
|Property||Range of maximum (diagonal) dimension of the part (mm)|
|Up to 10||Over 10, up to 30||Over 30, up to 100||Over 100, up to 300|
|Edge length, diameter (mm)||±0.2||±0.5||±1||±1.5|
|Angle deviation of prisms and plate||±30′||±30′||±30′||±30′|
|Width of protective chamfer (mm)||0.1–0.3||0.2–0.5||0.3–0.8||0.5–1.6|
|Stress birefringence according to ISO/DIS 10110-2 (nm/cm)||0/20||0/20||–||–|
|Bubbles and inclusions according to ISO/DIS 10110-3||1/3×0.16||1/5×0.25||1/5×0.4||1/5×0.63|
|Inhomogeneity and striae according to ISO/DIS 10110-4||2/1.1||2/1.1||–||–|
|Surface form tolerances according to ISO/DIS 10110-5||3/5(1)||3/10(2)||3/10(2) (all ø 30)||3/10(2) (all ø 60)|
|Centering tolerances according to ISO/DIS 10110-6||4/30′||4/20′||4/10′||4/10′|
|Surface imperfection tolerances according to ISO/DIS 10110-7||5/3×0.16||5/5×0.25||5/5×0.4||5/5×0.63|
6 Generating the drawing
Figure 1 presents a sample ISO 10110 drawing to show you how the information should be included to fully specify the lens. The drawing layout is the tabular form described in ISO 10110-10, and I believe this is the easiest ISO 10110-compliant layout to interpret .
The specifications and tolerances are from the ‘Typical’ columns in the tables above. Also notice that the dimensions are all rounded values. This is purposeful in that optical shops can measure only to a certain level of accuracy and specifying significant digits beyond that ability is meaningless. Additionally, if the lens is to be fabricated with a CNC machine, less digits to enter into the program means less risk of entering the wrong value. When optimizing your design, you will find that the performance loss is almost negligible when moving a radius from, say, 50.248765–50.25 mm.
7 Best design practices to ensure a successful lens
Now that you have gained some insight on how to generate an ISO 10110 drawing and what specifications are achievable, you may still have a lens that is difficult to make. This can be one of the most frustrating aspects of lens design for the beginner. The design will perform, the tolerances look good, and the drawing is complete, but the optical shop returns a ‘NO BID’.
In this case, there is just no substitute for experience. In Table 5, I have provided a few guidelines you can use to make sure fabrication of the part proceeds smoothly. Most of these I learned the hard way. A few thankfully were passed on by other designers. These are classic guidelines that you should always try to apply if you want to keep the cost down and reduce the difficulty of fabrication. Of course, some of these require a departure from the most optimal prescription. Do not get hypnotized by the merit function numbers: the optical designs can usually accommodate these guidelines with minimal impact on performance. They are by no means complete, nor do they apply to all cases. However, they will usually keep the beginning designer out of trouble.
|Center thickness||Minimum 2 mm center thickness, particularly for concave lenses||Thin glass warps easier under pressure applied during polishing, with increased risk of surface-induced wavefront error|
|Ratio of center thickness to diameter||Less than 12:1||Same as above. Thin lenses are more likely to flex during the polishing process, with detrimental impact on performance|
|Edge thickness||Greater than 2 mm (radius)||Thinner edges are easier to break, both during handling and after installation, if the assembly experiences vibration or shock|
|Edge diameter clearance for mounting||Minimum 2 mm up to 100 mm, 5–10 mm for larger optics||Aids in keeping stresses from the mounting interface away from both the clear aperture and the edge|
|Air gaps||Maintain minimum of 1 mm at center and edge||Aids the optomechanical design|
|CTE match for doublets||Match the thermal expansion of both glass types that make up a doublet within ~1–2 μm/m/C or less||Avoids temperature-induced stress at the glass interface, which can deform the wavefront or even pop the cement in extreme cases|
|Keep your lenses from getting too thick||I like to keep my diameter to center thickness ratios between 3:1 and 12:1||Reduce cost of glass and keeps the weight of the system down. Usually, a thinner lens will optimize out just as well as thick one, but step the thickness down manually a little bit at a time|
|Mechanical dimensions (center thickness, diameter, radii of curvature)||Round to the nearest 0.05 mm if possible. Match radii to the shop’s test plates and call out tolerances in fringes for large production runs||Reduces human error when copying values to CNC machines. Test plates reduce production cost|
8 Special consideration for American designers and optical shops
The ISO 10110 standard is very well thought out and is steadily gaining acceptance around the world. Contrary to Europe, however, outside of academia and drawings coming in from international business, the ISO 10110 standard has seen very little acceptance in North America. As large as the American market is, this fact of the current state of the optical industry cannot be ignored.
In preparing for this tutorial, I surveyed several American optical shops to gain insight into how often they handle ISO 10110 drawings. I found that 5–10% of incoming bid packages used ISO 10110 drawings. When I asked where the ISO 10110 drawings came from, I discovered that the overwhelming majority originated in Europe.
The United States currently has no optical drawing standard. Historically, MIL-STD-34 provided guidance for the generation of optical drawings in the United States . This standard was cancelled in 1995 and superceded by ANSI Y14.18M-1986. Y14.18M was never updated and is also considered obsolete. ISO 10110 officially replaced these standards. However, it was never designed to accommodate the notes-based drawing standards that the American optical industry have used for decades. Engineers and opticians trained in the United States simply find ISO 10110 counterintuitive after having used MIL-STD-34 and its replacement ASME Y14.18M-1986 for several decades.
In spite of their obvious shortcomings, the preference is to generate drawings loosely based on these obsolete American standards and simply resolve ambiguous callouts during discussions between the fabricator and the customer. Sometimes a drawing is not even used, and the shop generates lenses off of the customer’s original design file. An optical shop in the United States accommodates not only ISO 10110 drawings but also the obsolete American standards, drawings that are a mix of the standards, drawings that conform to no standard at all, and even design files where no drawings are generated at all. Needless to say, the American optical drawing system is very chaotic with no practical solution coming on the horizon.
9 Concluding remarks
The ISO 10110 standard is a serious effort to bring a standardization to a global market. As the drawing standard gains acceptance throughout the world, it is vital for the engineers and technicians in the optical industry to learn and understand how to interpret ISO 10110 drawings.
About the author
Jason Lane is a Senior Optical Engineer at Elbit Systems of America in Merrimack, New Hampshire. His current position involves optical lens design for use in thermal and visible imaging systems. Born and raised in northern Arkansas, he earned Bachelor’s and Master’s degrees at the University of Missouri – Rolla (now Missouri Institute of Science and Technology), both in Electrical Engineering. His career includes a decade of federal service as an optical engineer at the Naval Air Warfare Center, Weapons Division, China Lake, California. While there he gained invaluable experience designing, assembling, and testing imaging systems for use in guided weapons and weapons systems. After deciding that a decade of desert life was enough, he joined Elbit Systems of America in 2010 and moved his family to New England. He now claims to be one of the very few residents of New Hampshire to wear cowboy boots on a daily basis. His interest in optics spills over to his hobbies as well. He enjoys putting the Double Gauss and Tessars of the past to work in the form of classical film photography, and has been known to polish out the optics for an astronomical telescope or two.
I would like to thank my past and current colleagues, who as team members and fellow professionals have provided me the opportunity to pursue a profession in a field I thoroughly enjoy. For this publication, I would like to acknowledge the support of David Tourjee in contacting many of the vendors in the United States, who I spoke to in order to get an idea of how much ISO 10110 is used here. Finally, I would like to thank my wife, Kelly Lane, who somehow finds the strength and patience to put up with me.
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