In the process of refining the design for my 3D printed glasses (yes, I'm still at it 🙂) and trying to streamline the lens ordering process a bit, because some folks have told me their optician, or their optician's lens supplier, didn't really want to mess with "unusual" things like this, I decided to draw and print a fake ophthalmic lens. You know, not optical-quality - or even see-through - but something that looks and feels like a lens, that can be mounted in my frames, to show an optician hands-on how it works and that it's not weird or delicate to work on.
I figured it would be a quick print in clear PLA, that would require only a bit of cleanup and mount right into the frames, complete with the bevel and the notch and everything. How wrong I was...
This part is almost impossible to print right:
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It's modeled after a real bispherical lens with an offset optical axis. I mean it's optically incorrect, but it has everything a real lens would have: uneven edge thickness, one convex and one concave side.
You just can't set it flat on the bed in the slicer: none of it sits flat. The slicer has trouble generating support around the edge on the concave side that it interprets half of as overhang, and even if the beginning of the support doesn't get ripped off by the head and the print completes, the surfaces will be absolutely awful.
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If you print it vertical - which frankly is the least bad option - then the bottom of the lens, under the support, will be a complete mess. The bevel won't even be visible. It takes quite some time to create supports that won't mess up the bottom of the lens too much
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If you print it in clear PLA with only perimeters, it'll be transparent enough to see the spots were the perimeters are started at the next layer. And depending on your wall generation strategy, the spots where the printer tries to fill the voids will show up as round "halos" inside the lens.
The lens' thickness varies everywhere, so the slicer tries its best to fill each layer, but it's slightly different at every layer. At any rate, it reveals the slicer's idiosyncracies in tool path stragegy right away.
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The bevel all around the lens is only 0.5mm high. If the printer is dialed in, the bevel will show as an actual 120-degree bevel near the front face of the lens, particular where the bevel is normal to the layer, about half-way up the lens if you print it vertically. If not, it will look like a barely-raised blob.
I've tried this print on 3 different printer and I just can't get a decent print. All I can do is play with the settings in the slicer until it comes out not too terrible.
So, that part is a bit frustrating for my original purpose, but it turns out to be a great part to test a printer and/or the slicer software! If you want to try it too, it's here:
https://github.com/Giraut/3D-printed_eyeglasses/raw/refs/heads/main/lens_example.3mf
The other point here is that if the lenses a user gets don't quite match the frame you could always just tweak and reprint the frame a bit to match the lenses. That's not really the end of the world, but I don't count on any opticians to understand that. The concept of a user being able to so easily self manufacture a set of frames is probably completely alien to them.
Oh believe me, they understand perfectly.
Here's the thing - and I'm not inventing this: my current optician is a friend and she told me this verbatim: an optician's bread and butter is selling you frames, and the services around fitting the lenses on the frame and fitting the frame on you. Opticians make almost no money on the lenses - which they have made abroad in developing countries usually.
I don't deny that there's a lot of measuring prior to ordering lenses, counselling the customer, and then a lot of fiddling with the temples and the nose pads after the glasses are completed to make sure the glasses are comfortable and yada-yada. The services provided by opticians are definitely useful, particularly for young wearers and for people who change frames often.
But really, if you're a lifelong glasses wearer, you're reasonably handy and you settle on one frame geometry, those measurements never change and you just don't need the services.
Me, the last time I needed an optician's services was over 20 years ago when I made my first frames out of nickel silver. Since then, I've only made copies of those exact frames because I really like them - including those 3D-printed ones I drew a few weeks ago: they're a bit different to account for the nature of the 3D-printing process, but the key measurements are the same.
So whenever I go to an optician to order new lenses - which you almost have to because you can't order the lenses direct, even if you have all the measurements needed by the lens maker, the convo always goes something like this:
I kid you not, it's extortion. They hate it when you can do their job yourself so they charge you for the privilege. And since you don't have access to their suppliers (they look out for each other) you have to go through them.