Originally I wasn’t planning to do the lenses, but after I saw the white paper on using the clear resin to make camera lenses, I decided to give it a try. However, I wasn’t able to find info (admittedly didn’t look too hard) for corrective lens geometry equations. So, I got a dial indicator and measured my own prescription to reverse engineer the lens geometry.
I simplified the geometry to spherical surfaces and printed the mating surface to grind the lenses to a “perfect” spherical shape. In theory it makes sense, but in practice it’s not the easiest process. Ultimately use the dishes to rough sand the lenses to shape with 600 grit sand paper.
Then I used a wet sand paper and took the lenses to 1000 grit, then 1500 grit without the use of the dishes. Finished them off with a mirror finish polishing compound and a buffing wheel.
Lenses came out extremely clear, but there are little irregularities in the resin that prevent them from being perfect. However, because they were designed as prescription lenses I just hoped they improved my vision even slightly. Turns out they get me almost to 20/25-20/30. Amazing results. They have small impurities and the consistency of the lens is not viable for a replacement to my current glasses, but it’s a step in the right direction if you ask me. I plan to refine the process and see if these can give my regular glasses a run for their money.
Very nice. I had wondered if the there would be defects that you would notice being that they are right in front of your eye. Luxexcel uses a resin mist system that I imagine eliminates most of the imperfections you’re seeing. I spent about 11 years in an optical lab and if I can find the time, I can surely get you some formulas and such for prescriptions and prism. With lenses for human use, the two things you will notice wrong immediately are power and prism which will give you headaches. I’ll see what I can dig up for you when I get home.
Thanks! There are plenty of imperfections, some internal to the material (strange shift in the print), some surface irregularities due to sanding (1000 grit was done with small circles on lens, like waxing a car). There are a few sweet spots however that are really crisp, which give me hope! Wearing for more than a few minutes definitely gives me a headache though…
Some equations would be fantastic. I’m really interested in generating the geometry straight from a prescription. I have seen what Luxexcel is doing and it gave me the extra push to try on my own.
Niiice. I’d put that one above the camera lens story that was circulating last year. I just had to conjure up some greeblies for a company with a new logo:
Keep in mind that the two processes are very different so results may never match their resin mist. I think the sanding process will give you some prescriptions irregularities as well. Our process at the lab used fining and polishing pads on a machine that rotates the lens in a curved and circular pattern while spinning the pads along the surface. Fining pads dial in the power and polishing pads make it clear again. This is in conjunction with an optical plastic polish liquid. The polish pads were a felt material, so not sandpaper at all.
Trying to read your prescription and actually turning it into a geometry is an advanced task that was done by some expensive software. Maybe someone else can shed some light on that for alternatives. Base curve would be a simple geometry to get, but placing your pupil distance against the optical center with prism is going to be hard. Once done, you could take them into a vision center and have them check the power for accuracy on a Nidek, Humphrey, Focovision or whatever unit they have.
First off, thanks for the interest/feedback/expertise! Cool to see what this interesting group of users can come up with.
Absolutely, I am not trying to replace existing technologies (yet…) like the folks at Luxexcel are doing. I am just trying to get in the ballpark because it’s fun to think about tackling something like correcting vision with a 3D printer. I have thought about mechanizing the fining and polishing process with eccentric motion and CNC control, etc etc, but I’m more interested in using the 3D printer and basic tools as much as I can (making glasses for remote locations, like Mars when uncle Elon gets his act together). With optics, I know this is a long shot… but I’m curious now.
As for what I’d like to accomplish, standard lens shapes that can cover the bulk of human eyes, not so much the subtle nuances. Do you (or anyone out there) have formulas for the base curves?
I will try to find my ABO book with all that info. I can tell you, at least with traditional methods, the base curve is partially determined by the tooling chosen during generation, fining and polishing. Using this new method almost tosses that all out the window.
The following is a link from ABO about base curves. For reference OS = left eye OD = right eye and OU = both eyes.
What I found, and please verify if you’d be so kind!
The front radii of blanks are usually standard in the 6 diopter range, which equates to a radius of 337.5/6 = 56.25 mm, and based on my lenses which roughly have a 100mm radius on the outside, 337.5/100mm = a diopter of about 3.4.
With this info my right eye prescription is: SPH -2.25, CYL -0.5, ANG 127
SO, using this equation I found in the literature where Ft = Total lens power, Ff = Front power, Fb = Back power, n = refractive index 1.5403 for clear resin, and t = thickness at minimum in meters 0.0027m
With the additional cylindrical part of my prescription to correct my astigmatism, I’m assuming that the total power along the 127 degree axis needs to be -2.75, giving me a radius of 54.70mm at 127 degree and the 59.52mm radius at (127-90) or 37 degree.
You are on the right path, unfortunately, I never got that in-depth in certifications. I know the processes, equipment and a fair amount of the advanced optics, but that portion is outside my knowledge.
I made some Cuvettes for UV vis spectroscopy by spin-coating the 3D printed parts with uncured resin to make them transparent, and then curing them offline. Spin coating works a treat to get an even layer on your object! It might work with the lenses too. Not sure if the spinning/surface forces would work out on a curved surface. (worth a try!).
My aim was to test whether the spectroscopic response of the cured resin would interfere with the photo-initiated reactions inside the cuvette (and therefore other more complex fluidic components down the line). Initially the rough surface was no good for this application but I spin-coated mine on the inside and outside using a home built spin coater, and a curing box - I used a 365 nm wavelength domestic product which one of my colleague purchased previously. The cuvettes do become a lot more transparent. However small particles stuck to the surface and air bubbles can be a problem. But the technique is fairly robust to sanding/filing first. I think the secret is to be patient and to spin coat at around 2000rpm to create thin 200-300nm layers with many spinning/curing cycles. Patience is a virtue! I’ll post a picture when I’ve finished. It’s still a work in progress. If you don’t spin fast enough you get a spherical blob at the end of the object.
I’ll post a picture when I’ve finished. It’s still a work in progress. If you don’t spin fast enough you get a spherical blob at the end of the object.