Several labs are telling me no, (it stops at -18.00) but they can do it in 1.67. Anybody care to tell me why a higher power is not available in a higher index?
Several labs are telling me no, (it stops at -18.00) but they can do it in 1.67. Anybody care to tell me why a higher power is not available in a higher index?
The 1.74 blanks do not have as much thickness as the 1.67 blanks. I don't know why there are not thicker blanks available. It will probably come in time.
Epic Labs, through Soderberg, made a -25.00 DS +5.00 DC 1.74 for me a couple years ago (see pic below).Originally Posted by optical24/7
Jacqui could probably do it.
What frame did you use?
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Actually, the -18.00 sounds like the Varilux progressive limit. To my knowledge, Omega is the only lab that processes these.
Seiko has double aspheric free form lenses in 1.74 that go to -20.00
I would have to think there is someone making something that goes 1 diopter more than that....
PS. Robert that is a powerful pair of spectacles, what is that frame btw?
Talk to EPIC, although they are now an Essilor lab.
Logo Paris.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
Thanks Robert, I'll give them a call. Using a 50/17 plastic. I'll be working the POW comp numbers myself. (fwiw starting Rx is -17. OD/ -21. OS spherical.)
I'd give Quest Vision Care Specialty Lab a call on this one, Mike and his staff have done awesome work for me with prescriptions like the aforementioned.
Last edited by Paul Smith LDO; 12-02-2014 at 06:00 PM.
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Your welcome.
My example above was a 40mm eye (25mm DBL) that resulted in a 10mm thick lens, although there was 2mm to 3mm of decentration. As jspayneii points out, we're probably limited more by the blank edge thickness than by the ability to achieve a steep ocular curve, which I assume can't be done on a free-form generator, more likely on an older sphere generator, if that's the right term. I think it's likely that you'll have to reduce the eye size to the low forties, unless you facet or lay back the bevel, or use a lenticular form.
And like Chip always said, just make them good enough so that they can find their CLs!
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
1.74 is possible however 1.67 with minus base curve from X-Cell (-6.25, -4.25, -2.25) might be a viable option. I've processed high Rx's with both.
I avoid bi-concave designs when possible, but thanks all for the info and suggestions folks. And Robert, decentration will be .5mm OU (mono 33/33). I'll ask the lab what they estimate for bowl size, if needed I'll have it linticularized. ( Did I just make up a word?)
No, that's a real word (well, as real as any we use around here).
There are only two things that would make the lab unable to do it in a 1.74: Insufficient blank thickness, or inability of their generator to cut that high of a curve. I've noticed that the more "advanced high tech" a generator is, the lower the maximum curve it can cut. Depending on the generator, maximum curve can also be effected by crib diameter.
We'd have no issue doing it in a 1.74 most likely.
There are rules. Knowing those are easy. There are exceptions to the rules. Knowing those are easy. Knowing when to use them is slightly less easy. There are exceptions to the exceptions. Knowing those is a little more tricky, and know when to use those is even more so. Our industry is FULL of all of the above.
This is a -23.00 in a 1.74 I did a couple years ago. 5mm edge. I'll post this pic whenever I have the chance because they turned out wonderfully.
The ball cutter on a SGX is only so small making for lower ocular curves combined with the cutter being set at an angle instead of plunge cutting perpendicularly which creates limitations if you want to avoid crashing into the shank. That's just one machine example I have worked on and forget the old cup style cutters going that high. In the past I have cut the highest ocular curve I possible could and then made a hard plastic lap that I would outfit with a good quality first rough pad then literally fined the lens down to proper form. Often going through a handful of fining pads wearing our the grit. For blanks without enough thickness I would tape the back before generating and fine and polish before removing tape to create a quick and dirty lenticular a two part epoxy in place of tape makes for cleaner edges of the bowl or just polish the bowl edge by hand.
Of course without the equipment you need a specialty lab, good luck.
Good frame selection.This is a -23.00 in a 1.74 I did a couple years ago. 5mm edge. I'll post this pic whenever I have the chance because they turned out wonderfully.
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
Thanks. It goes without saying that if you're going to do powers like that then you should have frames that are suitable for them.
nice shotThis is a -23.00 in a 1.74 I did a couple years ago. 5mm edge. I'll post this pic whenever I have the chance because they turned out wonderfully.
Especially if you don't want a lenticular bowl. Notice the DBL, about 24mm to 26mm, the only way to center a 38mm to 40mm eye for an average PD of about 63mm.
It also looks like the hinge is way back from the front, allowing closure for a wide range of temporal thicknesses, with plenty of room to adjust the pads without interference from the nasal thickness of the lens. Note that there's plenty of space to add 20∆ BO/BI total to the present Rx when and if the occasion arises.
edKENdance, can we still get this frame? I ran out of the Logo Paris frames and don't like what I've replaced it with, quality-wise.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
It hasn't been listed as a current model for awhile now however the last time I spoke with the distributor and expressed concern about not seeing it he assured me that they were still available. I'm forever on the hunt for frames like this. If I recall correctly it's a 33 eye with a dbl of 30. There was another frame in the collection with similar dimensions to the Loop frame that I posted but it's not listed either. In Canada they're distributed by Dixit but I think it's Best Image in the states.
Does anyone know if freeform generators really can't go that high? I thought that the limitations came from the product specific math formula, meaning that as the power reached a certain level, the formula could no longer guarantee a level of performance required to be called whatever the product is called.
In other words, as a hypothetical, if auto III uses formula "a" to create a lens up to -10.00, if you were to use formula "b" as required by the demands of the rx, it could no longer be called an auto III. Just like ordering an auto vs an auto with attitude. With attitude uses a different formula and can therefore no longer be called an autograph
Thanks. Best Image rings a bell.
I think it's mostly a mechanical limitation; some fabricators have modified their generators to increase the parameter range, but the optics are going to break down at some point, and when they do, as is typical with prescribed prism and free-form, it gets ugly really fast.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
It's a mechanical limitation. Shamir can calculate lenses our generator can't cut. If you put in an Autograph III, and it can't calculate the lenses using the Auto 3 formula (whether its because of power, lens cutout, blank thickness, phase of the moon, base curve it wants not available, frame curve, etc.), it spits out an error message and won't create the files needed to generate the lenses.
It also depends on the brand of generator, and, as I've discovered, the crib size of the lens. I've reduced crib diameter on orders from 65 to 63 and had the generator be able to cut the 63mm lens (back curve was -17.40). As it was explained to me by the field tech, it's a matter of how far "back and out" the cutter can move before it runs out of space..
I just double checked on our SGX, and the steepest curve it will cut (base or cross) is a -20.00. So, on a 1.74, it would actually be able to cut the -21.00.
There are rules. Knowing those are easy. There are exceptions to the rules. Knowing those are easy. Knowing when to use them is slightly less easy. There are exceptions to the exceptions. Knowing those is a little more tricky, and know when to use those is even more so. Our industry is FULL of all of the above.
I could do this in-house with my trusty ole Optronics 2G.
Just ran the calculations using a blank from Younger (.50 Base) and it cuts using a 15.25 lap tool. Dummy frame used was a 40A 35B 42ED 20DBL, PD used was a 58.
It's very doable, the highest I've done on-site was a 1.67 -16.00 -4.00.
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Not saying it won't but eventually physical limitation comes into play, before you reach that limit chances are the manufacturers have set a software limit such as the -20, it might go higher but good design dictates leaving a buffer.
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