I am an optician who has worked for a mall-based optical chain and two different independent doctors of optometry, both with large retail sales. I now work as the Director of Education for an independent optical lab. I have more than twenty-five years “in the business.” I know exactly what optical products cost and how they are marked up. You are not going to read any “industry insider information” here, because none exists.
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What I can share with you are some common-sense guidelines.
Many consumers find our optician videos very helpful: OpticianWorks on YouTube
You can find great information on frame selection, lens choices and some of the language of the eyewear industry.
If I could give you just one piece of advice it would be this: You should feel both comfortable with and confident in the optician you are working with. If something doesn’t seem right, find another one. Think of the optician exactly as you would a plumber or car mechanic. If they can’t answer basic questions and their work turns out to be shoddy – STOP using them.
I am NOT selling anything!
I do NOT recommend any particular brand name products.
I do NOT accept advertising money from optical companies.
As a consumer, the first thing you must know is that you own your eyeglass “prescription.” Once your exam has been paid for, you may ask for a copy of it. By law, your doctor must give it to you. You are free to take that “prescription” anywhere you want to have your glasses made. Your doctor has no right to hesitate or refuse to provide you with your prescription.
Here is the actual law:
§456.2 Separation of examination and dispensing. It is an unfair act or practice for an ophthalmologist or optometrist to:
(a) Fail to provide to the patient one copy of the patient’s prescription immediately after the eye examination is completed. Provided: An ophthalmologist or optometrist may refuse to give the patient a copy of the patient’s prescription until the patient has paid for the eye examination, but only if that ophthalmologist or optometrist would have required immediate payment from that patient had the examination revealed that no ophthalmic goods were required;
(b) Condition the availability of an eye examination to any person on a requirement that the patient agree to purchase any ophthalmic goods from the ophthalmologist or optometrist;
(c) Charge the patient any fee in addition to the ophthalmologist’s or optometrist’s examination fee as a condition to releasing the prescription to the patient. Provided: An ophthalmologist or optometrist may charge an additional fee for verifying ophthalmic goods dispensed by another seller when the additional fee is imposed at the time the verification is performed; or
(d) Place on the prescription, or require the patient to sign, or deliver to the patient a form or notice waiving or disclaiming the liability or responsibility of the ophthalmologist or optometrist for the accuracy of the eye examination or the accuracy of the ophthalmic goods and services dispensed by another seller.
The use of the word “prescription” is misleading and it implies that the form you are being handed has medical value. It does not.
Currently, your routine eye exam consists of two parts.
1) A medical eye exam: Part of the exam is medically based and includes a thorough physical examination of the entire eye and visual system. This is often done with the eye dilated and it is when the doctor looks inside the eye with their bio-microscope. The medical portion of the exam can prevent blindness and detect a wide range of other serious health-related issues. Medical based eye exams are an important part of your overall healthcare plan. Medical eye exams are an objective screening tool. Everyone should get a complete medical eye exam at least every three years with every other year being a great idea.
2) Refraction: The other part of the exam called refraction is the determination of your eyeglass “prescription.” It is when you are looking at the eye chart and answering the, “which is better, one or two” questions. Refraction is a subjective, non-medical test, which in many countries can be performed by eye care providers who are not doctors.
“What is better 1 or 2?” is subjective. That means that you choose what you feel is adequate vision for you. It is a personal choice. You are free to decide if you are perfectly happy with your current “eyeglass prescription.” It is your CHOICE, your DECISION not your legislature’s, optician’s or any doctor’s to make. Not really much different than you deciding to exercise, smoke or take vitamins. It’s not anyone else’s business!
Prescriptions written for eyeglasses (not contacts) may, or may not, have an expiration date. This should only vary by any individual state law.
Shopping Online? – I’m Not Against It! More On That Below
Looking for something special, unique, something you are being told “can’t be done?”
You need to do two things:
1) Look for an independent optician owned shop.
2) Expect to pay out of pocket.
You will not, you cannot get custom work through a vision care plan.
Frame pricing is consistent throughout the industry. Almost all optical retailers mark up frames along similar guidelines. It is common to find identical frames selling for within a few dollars of each other in local markets. Unless the frame is unique to a very small vendor, chances are excellent that at least one other shop in town is selling the same frame. A little price comparison is always a good idea.
Frames are made by the millions, in huge factories located all over the globe. They are rarely hand-crafted in the back room at the shop.
You will pay more for a frame with a designer name. Frame manufacturers spend millions of dollars buying the rights to put designer names on their frame lines. They have to recoup that cost somewhere, so the higher the brand recognition is, the higher the cost will be. Stores will also charge a premium for exclusive brands, styles and the latest fashion trends in eyewear.
Designer frames look better than non-designer frames. Do not kid yourself. The frame companies know how to manipulate style. The best-looking shapes, styles and colors are combined in the higher cost designer lines.
Just because a frame has a designer name does not mean it is a better product. In fact, it was most likely made on the very same assembly line and from the very same materials as the company’s house brand. Heck it is even possible that a no-name or more generic brand name may be of higher quality than the fancy big-name designer line.
When you buy a frame, think about how and when you will wear it. If you wear your contact lenses 99% of the time, then buy a house-brand frame, and save your money. Does it really matter what your bedside readers look like? Do you need a designer frame for your computer glasses?
This video covers the basics of frame fit quite well.
Know that almost all lenses are made at huge factories or ground to order at places called wholesale optical labs, not behind the wall in your local optical shop. The fanciest and most expensive store in town may well be using the same exact optical lab as the discount place on the corner. Lenses may be ground to fit a frame in a shop, but rarely ground to fill an individual prescription.
Unlike frames, lens pricing is very inconsistent throughout the industry. Almost all optical retailers will mark up lenses to what the local market will bear. Of course, there are exceptions, and it is up to you to shop around and be sure you are not overpaying for a specific lens.
Single vision lenses: Single vision lenses are pretty basic stuff. If you have a low prescription, or wear your contact lenses most of the time, then just about any lens will do, yes even those bought online. If you have a higher prescription and wear your glasses all the time, then you will want to consider aspheric designs, non-glare coatings, and high-index materials (see below).
Lined multi-focal lenses: Lined bi-focals and lined tri-focals, the lenses with the “half-moon” segment, really have not changed much in the last twenty years. You will probably get what you had before and be pretty happy with them. They are also an excellent alternative to costly and compromised progressive lenses.
Obviously I could wear any lens I want. I actually prefer a lined bi-focal over a progressive.
Progressive lenses:
Not all progressive lenses are created equal.
To some degree you really do get what you pay for. Is $500.00+ a heck of a lot of money for some pieces of plastic? Yes it is. But, that is the way it is…
Beware The Smoke & Mirror Products:
Beware of glasses with switches, wires, knobs, batteries and any “new-technology” that has not been on the market for a few years and had the bugs worked out.
Don’t say I didn’t warn you!
Do know that all current, brand-name, lenses and many new free-form house brands are pretty darn good – to – excellent.
If you are being told that a certain lens is somehow above and beyond all others and is worth considerably more money than other lenses, you are being fed worthless sales propaganda.
There is no magic pixie dust!
Do buy a quality non-glare coating. Non-glare coatings allow you to see better, look better, and make for a better pair of glasses. Get the best non-glare coating you can afford. If you can afford it, get the good coating on every pair you have. Just like lenses, your optician should be able to tell you what brand and what type of non-glare coating you are getting and give you information about your coating. If you must choose between a cheap non-glare coating or none at all choose none at all. Cheap AR or non-glare coatings do nothing but scratch, smudge and smear.
Do ask about which lens you are getting. If your optician cannot tell you then you are probably being sold a very low-end product. Today the lenses being sold may not be a “brand name” but may still be of extremely high quality. Listen for terms like “house” or “independent” free-form.
Do try to buy a lens produced in the last year or two. Progressive lenses are still getting improvements, so many new designs are actually easier to wear than those made just a few years ago.
Do know that in the US your doctor determines your prescription, not your optician. So please do not get angry with them when a new prescription does not work for you. It would be (a little) like yelling at your pharmacist because your antibiotic did not cure your cold.
Do realize that if you are presbyopic (meaning that you need an add power, and should wear a lined multi-focal or progressive) and that if you have a change in prescription, that one area of your vision will be better and one will be worse!
PLEASE Re-Read that — Realize that if you are presbyopic (meaning that you need an add power, and wear a multi-focal or progressive) and that if you have a change in prescription that one area of your vision will be better and one will be worse! Stop torturing your doctor and optician! It is a simple fact that you cannot have perfect vision in all ranges. You are o-l-d. Get over it. If the doctor’s prescription provides you with crisp distance vision, chances are that you will lose some of the clarity that you had with near vision in your old pair. The only way around this is having individual pairs of glasses for the different ranges you need.
Do buy a BIG frame if you want a progressive to work well. If you want a progressive to work well, it needs room to do it. Yes, the optician will probably tell you it will work just fine, and the lens company will probably tell you it will work, but guess what? It won’t. Don’t say I didn’t warn you.
Pssst- Here is Insider Secret #1 that I will let you in on: Contrary to the ads you see, bifocal contact lenses rarely work very well! Or, they work for a year or so and then as you get older and your reading power increases with age they stop working. As we age our eyes also tend to dry out far more often making long term contact lens use less comfortable. So, don’t be surprised if your doctor is less than enthusiastic about you trying them. Your results may vary…
Do NOT buy the latest new thing, unless it comes with a 100% money back guarantee.
Is a pair of $500 glasses better than a pair of $200 glasses? Not necessarily.
Expect to pay about this much for a complete pair of glasses (frame AND lenses):
Single vision glasses: Between $30 and $500.
Lined multi-focal glasses: Between $150 and $500.
Progressive glasses: Between $250 and $700.
AR or non-glare coatings: add $85 to $200.
Changeable tint lenses: add $85 to $200.
Obviously some designer or specialty frames, gold, special materials all can fall in the thousands of dollars.
Know that a frame that has been returned can often be reused or returned to the manufacturer for a credit. Lenses, since they are ground especially for your individual pair of glasses and prescription cannot be reused and become trash. For that reason you must understand the reluctance of your doctor or optician to remake lenses without being 100% sure that they know e-x-a-c-t-l-y what the reason is.
For that reason you will need to explain to them what is not right about your prescription and/or glasses, not just throw them down and say, “These don’t work.” See: Why Can’t I See Out of My New Glasses below.
You cannot overlook a complete pair of glasses for $28.00 when similar or even identical products are selling for a hundred dollars more at the local shop. Online eyewear sales are a routine part of the business.
It IS possible to purchase a pair of perfectly good glasses online. Heck, I would say that your chances of getting a great pair of glasses from a large online retailer are actually better than what you might get through several of the managed care plan companies offered through your doctor’s office!
With that said, if you have a low prescription, you are looking for an inexpensive pair of glasses and you prefer to shop online then I would suggest going with one of the larger online retailers, Warby Parker and Zenni Optical seem to be the leaders.
Just like shoes or clothing you purchase online, for goodness sake, if your online glasses don’t fit, don’t work, give you a headache, well, then DON”T WEAR THEM – SEND THEM BACK!
PLEASE! If you are wearing progressive lenses and/or have a high prescription go and see a professional. DO NOT SHOP ONLINE for progressives or high prescriptions! The fit and measurements for progressives and higher prescriptions need to be made by a human. The choice of appropriate lens material and lens design needs to be made by an experienced optician.
You may also want to visit our YouTube Channel: Laramy-K On YouTube
Here is a list I am compiling of some frequently asked questions you are likely to have when you go to your doctor’s office or optical shop.
Q: How can I tell if my optician is reputable and competent?
A: You can’t. You can judge the likelihood of it by how long they have been in business and that they appear to be confident, competent and knowledgeable. “Certification”, since it varies greatly from state-to-state, is not a very good indicator of competence.
Q: Should I see a “licensed” optician?
A: Not necessarily. The only thing that matters in your optician is their level of experience and competency. Only half the states require a license anyway.
Q: Can you remove scratches from a lens?
A: NO! NO! NO! Your eyeglass Rx is created by the curves on the front and back of the lens. If you “buffed” out the scratch you would change the curve and you would change the Rx and/or create a big blurry spot. There is no “magic” liquid that can fill a scratch. Trust me if there was we would have it on hand for when we slip and scratch a new lens!
Q: Am I a patient or a customer?
A: When you are with the doctor you are a patient – when you are with an optician you are a customer. Glasses are two pieces of curved plastic held in place in front of your eyes by a couple pieces of bent wire. They are not a “medical device” and you shouldn’t be treated like they are. Your eyeglass shopping experience should be fun and entertaining not medicinal.
Q: What should I bring with me when I go in for an eye exam?
A: #1 Your eyecare insurance information. Know it before you go in! If you don’t know what it is then contact your company HR department and find out. Also bring a current pair of glasses, the box for both your R and L contact lenses if you wear them and a copy of your last written Rx if you have it.
Psst… Insider Tip #2: If you wear glasses then bring them with you to your exam. Don’t think that having the doctor “starting from scratch” will change anything. Don’t pull the, “Well you tell me doc.” The only thing that will happen is that you will seriously tick off the doctor! The very person that is trying to help you.
Q: What makes a high prescription?
A: Most opticians will consider a prescription “high” when it is over +3.00 or over -5.00. The higher the power of a lens the more important the frame fit and measurements taken are.
Q: Why can’t I use my eyeglass prescription for contact lenses?
A: Because a contact lens sits directly on your cornea. Every cornea has unique curves that must be matched to the lens for proper fit. Because the lens sits on the eye the power of a contact lens is often different than that for eyeglasses. Wearing a contact lens that is not fit properly can cause damage to the cornea. Unlike glasses contact lenses are a MEDICAL device and are not something to play with.
Q: When should I consider “high-index”?
A: When your prescription is “high” and/or your cylinder value (the middle number in your Rx) is over 2.00.
Q: Why doesn’t the reading area of a progressive lens go all the way across the bottom?
A: Eyeglass prescription are created by the curvature of the lens. You cannot overcome physics. The industry has thousands of doctoral level optical engineers working on making the best lens possible, trust me if it could be done it would be done. Just like with most things in life anything that does everything rarely does all of them well.
Q: What about all this blue-light stuff I see and hear about?
A: I’m not jumping down that rabbit hole. You’ll need to decide for yourself. My one word of advice would be if you are worried enough about exposure to blue light – spend less time on your electronic devices. Maybe go for a nice walk instead. If you are worried about a child’s exposure time, well, um, take it away from them!
Q: What is this free-form, digital, HD, stuff about?
optec contains other products and information you need, so please check it out.
A: The most direct answer is that a free-form or digital or whatever brand name they want to call it is a lens based on computer automated design or CAD. These lenses are created using very sophisticated computer programs and high precision tools to create special surfaces on both the front and back surfaces of the lens. The result is often a lens with a wider range of vision, increased optical quality and a prescription designed around the individual wearer and their frame. It is popular in progressives but can be done in high single vision prescriptions also.
Q: How do I know a frame fits me? Also see the video above on proper frame fit.
A: Look at 3 things. Width – Nose – Temple
Width: The temples or “arms” or “stems” should leave the front of the glasses and go roughly straight back and touch just before the ear. NO CONTACT with the side of your head!
Nose: Frames should feel comfortable on your nose. In plastic frames you want all or close to all of the frame touching the nose with no gaps and no single points of contact.
Temple: Make sure the temples are long enough to reach well behind the ear. In kid and petite frames make sure they are not so long they will be annoying.
If being fit for a progressive lens the optician must also consider the depth of the frame.
Q: Is the anti-reflective coating worth the money?
A: Yes, a high-quality one is worth every penny. I you need to choose between a cheap AR or none choose none. A high quality AR will have a brand name and your ECP should be able to tell you what you are getting. Most high quality AR coatings come with a two-year warranty.
Q: Do I really need sunglasses when the sun does not bother me at all?
A: If you go outside you should wear glasses with UV protection. While many clear eyeglasses lenses protect you from UV damage, all sunglasses do.
Q: Does a polarized lens offer more protection than a well made pair of sunglasses without polarization?
A: No
Q: Should I get the frames with spring hinges?
A: Not necessarily. Many frames today have flex properties throughout the frame making the spring hinge unnecessary. Frames made of super-strong titanium may not need spring hinges.
Q: Do frames with spring hinges fit better?
A: NO! If a frame is fit properly the spring hinge will be closed unless hit or being taken on or off.
Q: My vision has not changed in years. Why should I get a new exam?
A: Because an eye exam is not about getting the prescription for glasses it is about checking the overall health of your eyes. A good eye exam can check for diabetes, glaucoma, retinal problems, dry-eye and many other MEDICAL conditions that can lead to blindness.
Q: Why can’t I take my old lenses and put them in a new frame?
A: This can be done but it is like finding a needle in a haystack. In the world today there just simply is not time to do it and it is not worth the money. Lenses are cut for a SPECIFIC frame to within a 5/100 of a millimeter of accuracy. Forcing the wrong shape in to the wrong frame is not going to be doing you any favor.
Q: Why was the person at the optical shop such a jerk, acted annoyed, refused, rolled their eyes etc. when I asked for my PD?
A: If you are regular customer, get yearly eye exams, buy contacts and refer others to the store then that person should gladly give you your PD! If they do not they are foolish and rude. If you just wander in off the street and ask them to take their time to measure you for your PD so you can turn around and go and by your glasses on-line then you deserve to be treated rudely.
Q: Why can’t the optician tell how thick the edge of my lenses will be?
A: If the optician says, “There is no way to predict exactly how thick a lens edge will be.” Thank them and be happy you have probably found a competent optician! Lens edge thickness depends on material, patient PD, frame size, frame shape, the processes used to grind or create the Rx and of course the Rx itself. A difference of even 1/10th of a millimeter in any direction can cause a difference in edge thickness.
Q: Huh, what do you mean, my optician has a chart on his/her desk that shows edge thickness by material and power?
A: No, just no. Those things are marketing snake oil, BS.
Q: Why do some glasses cost so much?
A: You are paying for a brand name frame, you are paying for the research and development for the latest in lens and frame material technology, you are paying to make up some of the gap in income loss from the shop taking insurance, you want the very latest style from the famous high-end designer and you are willing to pay for it.
Q: Why did the optician look like they wanted to beat me with a stick and then toss me in a dumpster of hungry weasels when I kept comparing my old pair to the new pair I just got?
A: Because your prescription and/or frame changed! Of course things will look a little different between the old and the new pair. If they did not then you would not have needed a new pair of glasses. Yes, a change in frame can cause a change in vision even in the same prescription (due to different angles and distances from your eye). Remember YOU chose the Rx by saying 1 was better than 2 etc…
Q: Why can’t I get my Rx in those cool wrapped styles I see?
A: Depending on your Rx you may be able to but expect to pay well over $500 to get it done. Eyeglass prescription are created by the curvature of the lens. You cannot overcome physics just because you want to look cool. The higher your Rx the less likely it will be that you can get it filled in a “wrap” frame. I do NOT endorse any products however Bolle, Rudy Project and Oakley do offer some of their wrap designs in Rx.
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LOL: A customer called and asked, “If I bring my glasses in can you fix them?” He replied, “Well I might have a much better chance that way instead of over the phone!”
LOL: A customer called and asked, “How much are your glasses?” She replied, “How much is a car?”
LOL: “No I did not use Super Glue on them.”
LOL: “I need a screw.”
LOL: A daily occurrence in an optical shop – A customer brings in a pair of glasses with both lenses out, the temples bent and the temple end cracked and says, “I just opened the case and they were like that.”
OK, this is a tough one and I could go on for hours… A competent optician working with your eye doctor should be able to trouble shoot a prescription problem, in one visit, 95% of the time. 5% of you out there need to remember that you see with your brain, not with your eyes and maybe your brain is not working quite right. That is not meant to be mean or sarcastic, it is quite simply the truth. Yes, you may be in that 5% group if you have been back more than twice for a prescription problem. If you have been back three, four, five times then you are in that 5%!
Vision is subjective not objective.
STOP comparing your old pair and any new pair. As stated above, as we age if your Rx changes you will gain and lose perfect vision in one area or another.
Vision is the result of the brain interpreting what it sees through BOTH eyes. STOP covering one of them and insisting there is a problem.
If you have a pair you like and work well for you then BRING THEM WITH YOU when you take your new glasses back to the store.
Many small problems with a new Rx can be overcome with simple adjustments to the frame. This may seem a little odd but it works, it works!
If your prescription changed and it now calls for an add power but you choose to not go in to a bi-focal or progressive lens you are probably going to be unhappy! You are old, o-l-d, get over it.
Single Vision: If you are a routine prescription and you wear single vision glasses and you cannot see well out of your new prescription then chances are excellent that you need the Rx tweaked closer to what you were wearing previously and liked. Have your optician:
Note: In very rare instances a change in material can cause problems with an Rx.
Lined Bi-Focals and Lined Tri-Focals: If you wear a fairly routine prescription and you wear a lined bi-focal or lined trifocal and cannot see out of a new Rx then you will need your optician to run through the same checklist as above for single vision. However if the line is placed too high or too low they simply need to remake the glasses. Note: The height can often be adjusted a few millimeters up and down with the nose-pads on a wire or metal frame. Lenses made too high or low in a plastic frame MUST be remade.
Progressives:
After ruling out the checklist above for single vision:
Every progressive lens has special embedded proprietary markings and an individual fitting layout chart. They should use those marks and highlight them with a special pen. Then check that the lens measurements match those written on the job order form. Only then should they put the glasses on you and look at how they align with your eyes. Common errors (we are human) are fitting the distance area too high or too low or missing that one eye is much higher or lower than the other.
Any reputable optician or ECP should be able to explain, in simple terms, what you are buying. Here is a list I am compiling of terms you are likely to hear when you go to your doctor’s office or optical shop.
Many consumers find our optician videos very helpful: OpticianWorks on YouTube
You can find great information on frame selection, lens choices and some of the language of the eyewear industry.
Aspheric: A lens that is designed with special curves that makes the lens thinner, lighter and provides better vision.
Astigmatism: All it means is that your eye’s cornea has two different curves on it. It is a scary sounding word for a very simple refractive condition. We have a free video on it.
Plastic: Virtually all eyeglass lenses are now a type of plastic. A lens called “plastic” is one made from a material called CR-39. It is heavy and quite thick but is quite good for lower prescriptions, tinting and optics.
High-Index: A material that provides the thinnest (NOT LIGHTEST) possible lens for higher prescriptions. High-index lenses will have a number from 1.60 to 1.74. The higher the number the thinner the lens should be.
Trivex: A lens material that is lightweight, and has great optics. But – Can be quite thick in higher prescriptions.
Progressive & Transition —
Transitions Lenses®: Is a brand name for lenses that darken when you go outdoors. Transitions (the word) has become a generic term for darkening lenses. Darkening lenses are an excellent choice for anyone who frequently goes from inside to outside. Darkening lenses do not stay dark in a car so they DO NOT replace sunglasses.
Progressives: Also incorrectly called no-line bifocals or no-line trifocals. These are lenses that provide the full range of vision from distance to intermediate to near with no visible lines.
Polycarbonate: A thin, lightweight, lens material with fair optics. Polycarbonate is used in over 80% of all eyeglasses because of its low wholesale cost and low weight. It is NOT a high-index lens and it is NOT the thinnest lens available. Polycarbonate once coated is NOT safe, impact resistant or offer any kind of special protection.
Non-Glare: Also called anti-reflective or AR is a special coating that allows more light to enter the eye. More light = More sight.
Single Vision: A lens for one fixed distance, not a bifocal, trifocal or progressive lens.
Distance: A lens or prescription for distance viewing only: Examples, driving, watching a football match, sightseeing.
Intermediate: A lens or prescription for intermediate viewing or roughly at, or just beyond, arms length: Examples, computer screen, grocery items on the shelf, sheet music on a stand.
Near: A lens or prescription for near work or less than arms length: Examples, threading a needle, reading fine print, removing a splinter.
Computer Progressive: Also called office progressive. A progressive style lens designed for only intermediate and near work. An office progressive will allow comfortable intermediate viewing with the head in its natural position. These only work in the office environment!
Free-Form: (Digital) (“3D”) A special computer generated technique of making a lens that provides the best vision. Lens may require special measurements be taken.
Digital: (Free-Form) (“3D”) A special computer generated technique of making a lens that provides the best vision.
Temple: You might call it a “stem”. The piece that holds the front of the glasses the chassis that goes back to your ear.
Prism: A technique using the eyeglass lens to alter the position of an image being viewed so it appears to your brain that it is in the correct place and in the same position as the other eye sees it.
PD: Patient PD or patient pupillary distance. The measurement between the center of the eyes (actually the eye’s visual axis). Can be measured from eye to eye called binocularly or from center of nose to center of eye for right and left called monocularly. Very important in high prescriptions and for progressive lenses, not so important in lower prescriptions. As in anything less than 1.00 diopter it really doesn’t matter at all.
Fitting Height: The vertical measurement of where the distance portion of a progressive lens will be fit. Unique for every different set of glasses and every individual person.
Polarized: Polarized: A sunglass lens that has a special polarizing filter. The energy that we perceive as light travels in both horizontal and vertical waves. A polarizing filter cancels or blocks the energy moving along the horizontal plane, or the light that we perceive as glare. Nice to have but NOT necessary.
The glass types selected for an optical component or system can have a noticeable impact on price, lead time (both initially and on an on-going basis), manufacturing yield and performance.
In our experience of designing and manufacturing many thousands of custom optics over 40 years, customers come to us with designs that are optimized for performance but not always balanced by the impact on cost and delivery. The following are suggestions and things to think about to help you achieve that balance.
There are currently hundreds of different glass types available with prices ranging from $9 to more than $780 per pound. The percentage contribution of glass to the total cost of the optic varies.
In the case of a large optic that uses rare glasses, it can be 70% or more. Typically, the range is 20%-30%. In either case it’s a significant cost factor. And, that’s just the direct cost. There are also the indirect costs of manufacturing yield and availability.
The leading optical design software packages (e.g. Zemax and Code V) offer a feature that allows you to set a “not to exceed” price when the software runs its glass selection routine. If you don’t like the resulting performance you can always raise the price cap.
By starting with the lower price glasses you’re more likely to find the sweet spot between performance and cost.
Use the glass manufacturer’s Melt Frequency-Relative Price Chart to manually create custom glass substitution catalogs in your lens design software program. The program will only use glasses from this list when evaluating alternate glass types.
Each of the major glass manufacturers (e.g. Schott and Ohara) publishes melt frequency data (see Ohara example) for their glass types. Consulting this information is important since the preference is to use more readily available glass types. This will shorten initial delivery as well as improve lead time for subsequent production.
An additional step is to call your optics vendor. They buy glass regularly and are in contact with the glass makers and their resellers on an on-going basis. They have a good sense of glass availability and, if in doubt, can get in touch with their glass source for more information.
Some glass types are more susceptible to staining during manufacturing. Stains can result from environmental conditions in the manufacturing area (e.g. high humidity) or from the polishing compounds used to make the optic. Optics makers are constantly improving their manufacturing processes and environmental controls to minimize these impacts. However, you can help your project by selecting glass that has good environmental resistance characteristics.
There are only a few companies that make a full range of optical grade glasses. Schott, OHARA, CDGM, Pilkington, Hoya are the principle players. They each have their pluses and minuses with respect to breadth of product line, consistency across melts, delivery, availability and price (as much as 30%).
The major glass makers offer comparable product lines of glass types which means you have options. It will help your optics manufacturing vendor do their best work for you if you give them the choice of which glass maker to use. They can apply their experience and knowledge about optical glasses to your products and build flexibility into your program throughout its lifecycle. If there is a shortage or delivery delay from a given glass manufacturer, you may be able to avoid late deliveries to your customer by switching to the more available equivalent glass.
If you decide that you need to specify a glass manufacturer for your optic, it’s worthwhile to get your optics manufacturer’s recommendations. You’ll be better served by specifying a glass manufacturer that has the confidence of your optics maker.
Customer will sometimes request optics with index of refraction and/or dispersion tolerances that are tighter than standard, and beyond what the application requires. Often the tighter tolerances are boilerplate on the customer’s drawing. In order to achieve tighter tolerances, glass manufacturer’s do a post-production sorting. This translates to more cost and potentially limited availability. The standard tolerances offered by the major glass manufacturers are adequate for the large majority of applications.
Unless your tolerance analysis suggests that the design is sensitive to index of refraction or dispersion variations, you should be able to use glass with standard tolerances and get great results.
Standard Index of Refraction Tolerance (Nd) = 0.0005
Standard Dispersion Tolerance (Vd) = +/- 0.5%
The smaller the optic the less likely it is that it’s worth paying for a higher than standard homogeneity classification. Homogeneity is the variation in index across the glass blank. Since the rate of variation is small, the smaller the optic the less value there is in having a homogeneity certification. Essentially you’re paying to certify something that you are getting anyway.
We use the rule of thumb that an optic with a diameter less than 1” or 2” does not require higher homogeneity. Larger sizes are dependent on the application requirement.
The reasons size matters with respect to glass are twofold. First, the obvious – larger optics require more material resulting in a proportionately higher material bill. The other reason is based on the standard slab size of raw glass. Glass manufacturers produce raw glass in slabs. If your design requires an optic larger than the standard size will yield, the glass manufacturer needs to deviate from their normal manufacturing processes. This translates to higher cost, longer lead times and availability issues.
If your application requires optics that clearly exceed the standard slab size, then it is what it is. If not, then it may be worth a few additional design iterations to see if you can get within that standard size.
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