What is Minimum Blank Size (MBS) and How Do You Calculate It

A lens blank must be large enough to be cut to fit a specific frame while also allowing for decentration. The larger the frame and the more decentration required, the larger the uncut lens blank that will be required. The MBS or minimum blank size calculation lets you get a good estimate on the blank size that will be required to get proper lens cutout. Watch and work through the calculations to determine lens minimum blank size or MBS
Learn More: opticianworks.com/
This week we work through the calculation to determine lens minimum blank size. A lens must be large enough to be cut to fit a specific frame while also allowing for decentration. Opticians use MBS when doing optical lens finishing work. The larger the frame and the more decentration required the larger the uncut lens blank that will be required. Optician training includes calculations for lens finishing and lens minimum blank size. The MBS or minimum blank size calculation lets you get a good estimate on the blank size that will be required. MBS applies to both finished uncut lenses and surfaced lenses. Opticians will use MBS when ordering stock lenses to fill eyeglass prescriptions and when working with their wholesale optical lab.
Learn More: opticianworks.com/
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This video lesson is sponsored by Laramy-K Optical
Laramy-K Optical is a digital uncut and coating lab unlike any other. The only exclusively uncut lab in the country; we provide our customers with independent, high-end alternatives to corporate brands. Through craftsmanship, technology, and independent, innovative vendors like Younger, IOT, A&R, and Quantum Innovations we offer our customers the Integrity portfolio of freeform lenses and coatings. Made in the USA, the Integrity brand is not a generic house-brand, but is the absolute best available, designed to give the wearer that “wow!” experience.
In addition to the digital line, we still offer conventional surfacing, including glass. Maintaining traditional equipment gives our customers vastly more flexibility in their dispensing, particularly when it comes to more difficult prescriptions.
Learn More: www.laramyk.com

[@sophiamoh292]

loved the dramatic music for the big lens! very entertaining! :D

[@mrod26]

I have been working in a digital eye lab for a while in all the areas and I always wondered about the cut out whenever I was in the finishing department, Thank you so much for your videos, its easier now for me understand so many things at my job!!!

[@LaramyKOptical]

So glad to hear it, M! Thanks for taking the time to comment.

[@elmeralvarado1236]

awwh man!, that epic reveal song for super lens is helping me pay attention, at 12:49am

[@GuadalupeGarcia-zp5fn]

I am so grateful for all your perfect explanation thanks !!!

[@LaramyKOptical]

You are welcome. John

[@rolaqaryouti2729]

You are awesome ..thank you very much for taking care of optical word ..and explaining this topic 🌸

[@LaramyKOptical]

You are welcome - thanks for posting. John

[@rake48llll85]

Just a note......I was having difficulty until I wrote out the formula to read ED + (2 x Decentralization) +2. Thanks for the help understanding this concept.

[@LaramyKOptical]

Kevin, Yeah sorry about that... my math skills are, well, kind of awful really. Glad you sorted through it and got what you needed. John

[@rake48llll85]

No problem. Only suggested it because there will be others that may make the mistakes I did. Thanks for doing these videos. You do a great job.

[@LaramyKOptical]

;-) There is a reason NASA isn't hounding me to come and work for them... Just be glad I'm not doing videos on determining structural loads on multi-lane inter-state highway overpasses.

[@celinecelinecelinecelineceline]

Very nice explanation for my upcoming test! Thank you!

[@LaramyKOptical]

Thanks for watching, Celine!

[@redbecca3242]

Hi! I've been loving the videos, I did some advanced dispensing training in my old store but never fully grasped it, your videos have really helped me, even doing some more complicated things I didn't expect to! I was wondering if you have any videos on calculating lens thickness and sag? I know the formula but really need some explanation of how it works, thank you! :)

[@LaramyKOptical]

Sorry but no we don't and we never will. That is wholesale surfacing lab stuff not optician stuff. We do have a piece coming up about material and thickness but that is about as far as things will go. Lens thickness especially when related to sag and the somewhat complicated formula used to calculate it falls in the show-off category for me. It's fluff that is totally unrelated to what an optician needs to know. We had to to do it in school but that was because we also did old-school surfacing. That sort of thing is entirely computer based now. John

[@user-jo1ju6im5k]

Thank you sir for explanation in Minimum Blank Size.

[@tohirikagawa2919]

Ok, it's very helping for order lenses..

[@iMuayyad]

Thank you sir for the amazing explanation, sir I have a question .. how about if there is a vertical decentration for the same example ?

[@LaramyKOptical]

A is always wider than the B so not really a concern.

[@Fractal8359]

Is the reason for doubling the decentration measurement just for good measure or is there a more important reason behind it? I can't see way you would want to account for double the decentration per lens, it seems you would always end up over estimating the needed black size. To use your example if the decentration measurements are 4 and 2 why would MBS 61 and 59 be incorrect?

[@Loyaltytrades]

Is that the formula to use for ABO too?

[@LaramyKOptical]

Ms. A, Can't say for sure if it is on the ABO. If the ABO has a question about MBS then they sure as heck better be using this one! But, you never can tell - I have no "insider" information on the ABO. John

[@destyneeturner9326]

Everytime you pick up the super super lens and the music plays I giggle. Now everytime I do a MBS I'm going to hear that!!

[@LaramyKOptical]

;-)

[@aimeevictoria18]

I’m really new to optics, trying to learn as much as possible. One question, what does ED actually stand for?

[@LaramyKOptical]

Effective Diameter. John

[@majesticoptics7094]

Thanks For the video, actually how could we measure the perfect ED ?

[@LaramyKOptical]

kzbin.info/www/bejne/hGi7oqelgtGfbqM

[@fantacalexain2665]

I am very new to optical, and don't cut lens here so if this is a stupid question i am sorry. If you use the 65 mm for right and 61 mm on the left wouldn't that make a big difference in the thickness of the lens, or does the decentration compensate and it ends up the same?

[@LaramyKOptical]

I'm not 100% sure exactly what you mean but I'll give it a try. Short answer: the more you have to move the lens within the eyewire the more some edge of the lens somewhere will be thicker. Big-picture it doesn't even matter if it is plus or minus. The less you have to move it the more EVEN the edges will be all the way around the lens. Beyond that you have thickness issues in plus that you don't have in minus. If you are talking about single-vision-finished-uncut lenses ("packaged" lenses) then you might well have a thicker center on a plus 65mm blank than you would on a 61 even if they were both +2.00. I think you are actually looking for this one: kzbin.info/www/bejne/pJraaaqdorepgbc You may also find the finishing course helpful! John

[@gayanrukmalmarasinghe6492]

If the Dec is vertical from the GC... How measure MBS?

[@LaramyKOptical]

The B is so rarely longer than the A we don't really think of it that way or apply the MBS formula to it. If you have enough vertical decentration to not get cutout you have a problem. Progressives are designed to accommodate, SV should never need more than 5mm or so.

[@Biorbboy]

Hi Larry, Quick question. I have a member of staff who calculates MBS at 60, however, oddly orders MBS much larger as she claims that the lenses are more cosmetically appealing.... I would have though one would order to the MBS as this would result in a lens with reduced weight and central thickness in say a plus lens... surely the sagittal thickness increases with blank. Thanks

[@LaramyKOptical]

60? 60 what? Randomly picking 60? I need some more to go on here. ED is frame dependent, PD is human dependent, I don't see how 60 could ever be a fixed part of the "formula." As a + lens gets bigger the center thickness increases period - end of statement. To get the thinnest plus lens you must input all the correct parameters and let the software sort it out. In minus it doesn't matter all that much at all. I think your staff member doesn't know quite what they are doing/talking about????? John

[@gavinhughes5386]

If I was asked to find blank size required using 'laying off' what would this mean?

[@LaramyKOptical]

No idea at all! Laying out perhaps? That is the term for setting up a lens for blocking and finishing. In that case yo have some videos and the open Finishing course too. John

[@ccm31296]

My husband heard me watching this video from the other room & he said "are you watching Bill Nye???" & I said "uhhhh it's pretty much Bill Nye for glasses"

[@LaramyKOptical]

Thanks! John

[@giordanopioli1922]

Here I am again. I find the information you provide to be very helpful. I have a question: I have to make a +3.50 rx pair of glasses. From what I learnt on the net I understood that, especially for plus lenses (in minus lenses the thick part is cut out), stock lenses will be thicker than surfaced lenses; this is much noticeable with smaller frames, as stock lenses are usually bigger than the minimum blank size. Is this right? If the optician suggests me to make the glasses with stock lenses, should I opt for surfaced lenses instead? Do all optic laboratories surface lenses to the minimum blank size? Or do they manufacture surfaced lenses just the same as stock lenses and then cut them to the frame? Thank you!

[@LaramyKOptical]

Excellent point! You have repeatedly said you want the thinest lens possible. In that case you would be correct in wanting a surfaced lens that has been designed around the frame (shape/size) that you choose. That would be the only way to be 100% sure. John

[@giordanopioli1922]

Ok. So should I simply request for a surfaced lens or should I request for a personalized one, like Zeiss Optima? Do they consider these things when normally surfacing lenses or should it be specified and requested? I think there would be quite a difference in price for normally surfaced or personalized ones, like Zeiss Optima line. Furthermore I asked informations about Zeiss Optima to my optician and if it would be suitable. My optician said that they usually do Zeiss Optima lenses when there is a big difference in prescription between the two lenses. @@LaramyKOptical

[@LaramyKOptical]

@@giordanopioli1922 All customized or personalized lenses are surfaced. Your call on choosing the upgrade to that over a conventional lens.

[@giordanopioli1922]

I'm sorry, I don't understand, maybe for my english :) All personalized lenses are surfaced. What isn't clear to me is if all surfaced lens are personalized. Or should I request for personalization even when if I requested for surfaced lenses? Does doing surfaced lenses imply personalization of the lenses or should I request for the personalization further to the surfacing? I apoligize if I'm bothering you :)@@LaramyKOptical

[@LaramyKOptical]

@@giordanopioli1922 LOL ALL personalized lenses are surfaced. NOT ALL surfaced lenses are personalized. You will pay more for a personalized lens. It is the difference in how the lens is cut. There is no such thing as a stock, personalized lens.

[@mikm9075]

Great video but I'm confused...ok for ED.. but how can calculate MBS if I change optical center height also??

[@LaramyKOptical]

Mik m, Wow great question. Took me a few to figure out the answer... Unless the frame was a very unique shape your B is (almost) always narrower than the A so no need to account for it. Yeah, I suppose you could run into that one-in-a-million situation but you will now be prepared if that should happen. John

[@mikm9075]

Laramy-K Optical thanks :)

[@whimsandworries]

my favorite character in these videos is Super Lens :D

[@Sunflowerprincess88]

Your video was very helpful, I am currently studying for my exam, but first I have 2 practice exams. Your video helped a lot, but I do have a question about a problem in my exam book. The question reads: a frame that measures 54/20 with and ED of 57mm is selected by a person for single vision lenses. If each lens must be decentered 5mm in, then the minimum blank size needed to complete this job is 68mm. The answer is 68mm, but with the MBS formula I am using, I think I may have a number off, because when I plug in the 57mm + 2 (5) +2 = 69. I think I may have missed something here. It's only one digit off. Can you clarify? The A and DBL in this problem is not given here, so I only went with what they gave me.

[@LaramyKOptical]

Sorry but I don't supply support for questions that are not mine. Should be plenty of good examples in the video and on the OpticianWorks website. John

[@kenhong7732]

Is it necessary to measure the frame curve when we calculate MBS?

[@kenhong7732]

Some people prefer to use the sunglasses frame but sometimes I have to order much bigger lenses to fit in the frame. That makes me confused.

[@LaramyKOptical]

No, not necessary but frame curve is a huge part of lens-frame matching. It is a very complex subject we hope to tackle this year. It is so complicated and has so many myths attached to it that I'll need help from several outside sources.

[@kenhong7732]

thank you so much.

[@ACrimingShame]

We use this formula A+Dbl+ED-PD so if this was a plus lens and in your example the addition = 68+55-32=61 Id order 65 stock lens as plus single vision let’s just say you would want as close to number where as if the was minus single vision Id order a 70 stock lens ... when we do any progressives plus we always califit

[@LaramyKOptical]

Well, like I always say --- if it works keep doing it! As I mention it is not a formula or an exact method just a rule-of-thumb. John

[@coreRAGEious]

Hello. I have a question. I know I’m about 6 years late lol I’m trying to get abo certified and am running into a practice question that I can’t answer however the question itself seems pretty straight forward. Hopefully you can answer this for me. The question is, what is the mbs of a frame that’s 54-19 and ED of 57 and a patient PD of 38. I have done this formula many times over and everytime I add the ED my answer is way higher than any of the four multiple choice answers. Any advice would be greatly appreciated!

[@LaramyKOptical]

38 isn't a PD. Bad question = no right answer. I would assume it should say 58.

[@coreRAGEious]

@@LaramyKOptical I also think it’s a bad question. It’s part of this course that I’m trying to learn. If I had a pic I’d send it to you but nonetheless this is how the question is worded. I tried working on it for almost 45 min before I got frustrated so the fact that your even telling me it’s a bad question says a lot about this course haha I appreciate your time

[@LaramyKOptical]

@@coreRAGEious That is why you should only use OpticianWorks.com to study! ;)

[@bpark10001]

You need to draw around your lenses with a marker so they can be seen (they are invisible in the video).

[@LaramyKOptical]

Good idea Brian. Thanks for the suggestion.

[@LaramyKOptical]

Yeah, I noticed that too! Sorry about that. I'm on it. Great suggestion. John

[@ericpham8205]

Optical computing is like analog rather than digital and that how your speed and quality and quantity improve

[@ironwithin3875]

can you turn the sound effects down, most of the time it drowns out what you're saying

[@ShubyDuan]

Can decentration be negative? or would you take the absolute value anyways?

[@LaramyKOptical]

Negative would be he incorrect term but yes you can have out decentration if the persons eye sits out from the eyewire lens opening. You need to watch the videos on decentration and then start drawing things out.

[@ShubyDuan]

@@LaramyKOptical I understand decentration can be in any direction. I just meant from the context of using that formula you have on the board. My guess is no, it’s always a positive value.

[@LaramyKOptical]

@@ShubyDuan I can't say with 100% certainty but I wouldn't think that tossing in a negative number would be a great idea. In the 1/1000 chance you have out decentration that should be working in your favor for MBS anyway.

[@ShubyDuan]

@@LaramyKOptical sounds reasonable. Thanks for the discussion

[@brandoncheung3003]

@@LaramyKOptical This is what I have been trying to figure out before I take my national exams tomorrow. So from my understanding, even if the PPD is larger than the Frame PD which therefore would result in a negative (-) decentration value.. In regards to actually plugging it into the MBS formula, we would use the decentration value as an absolute and not include the negative (-)?

[@edwinchen5529]

Owhh i tought mbs was (GCD-patient pd)+ED

[@RoyRosales]

I'm surprised you didn't touch on the fact that a lens can be generated with OC decentered on lens. Very often used with large frames (safety/sport frames) where the eye is relatively very close to the nasal compared to the temple. If the lens is generated with the OC in the center of the blank, you are forced to generate a huge blank, and you waist a lot of lens.

[@LaramyKOptical]

Good call... We do cover that in a few of the other videos. I do mention "the lab" in a few places and anything that isn't stock would be surfaced with ground in decentration if necessary. It kind of goes without saying but it might have been worth saying it anyway. John

[@RoyRosales]

Oh great! I assumed this was the end of this topic. I look forward to seeing the other videos. Great work all around.

[@LaramyKOptical]

kzbin.info/door/dfKXBLjBDbX2X2g0XuAbmwvideos

[@TayyabHussain253]

What’s ED

[@LaramyKOptical]

Effective Diameter See: kzbin.info/www/bejne/hGi7oqelgtGfbqM

[@riddhishah7968]

I m confused what is the 68 ???

[@LaramyKOptical]

Start at the beginning! Watch the video on The Boxing System first. John

[@riddhishah7968]

@@LaramyKOptical ohk thank you

[@zias165]

Sometimes This formula doesn't work!!

[@ericpham8205]

Therefore no need of blank size