I’ve been following the YouTube channel Breaking Taps for quite a long time. It’s a fun mix of science, engineering and technology covering physics and the occasional bit of chemistry with some just flat out cool experiments, crazy tech and fascinating slow motion in between – like that time when he made his own scanning laser microscope (it’s pretty cool, you should watch it).
Well, now he’s having a go at making some optical lens elements. And it turns out, making lenses from epoxy resin is a bit more difficult than one might initially think.
He’s not making elements for the type of lenses we’d typically use on a camera, but elements are elements. They all work on the same basic principles. To copy optical elements, though, it’s not simply a case of encasing an element in silicone, grabbing any old epoxy off the shelf and casting it into the aforementioned mould. There’s a lot of caveats and the overall technique is one that is going to require a lot of testing and workflow refinement to get perfect.
There’s the fact that at least some types of silicone will stick to the types of glass often used for lens elements, making them difficult to cast without some kind of mould release, or covering the optical element in something – both of which will deform that smooth glassy surface to some degree. You’ve got shrinkage to take into account, too – Epoxy resin will typically shrink as it cures, potentially resulting in an element that’s smaller than it should be. And then there’s air bubbles to think about.
And those are just issues in replicating the element’s shape and surface and making sure you can see through it properly. This doesn’t even touch on things like internal stresses or the index of refraction of different types of resin vs optical glass. As soon as you change the material, the same structure doesn’t necessarily bend the light in the same way and the internal stresses of the material as it cures can mean that the index of refraction is different throughout your element, causing all kinds of potential visual issues.
Some of the challenges can be overcome simply by making smaller optics, but that isn’t always possible. It’ll depend on your needs and the optics you have at your disposal that you wish to clone. Scaling it up to larger optics will definitely be a challenge, but it’s one that BT plans to tackle through experimentation with different casting and moulding materials.
If the technique can be refined, I wonder if this would allow for the creation of new custom lens element designs in the computer to prevent the need to have an actual pre-existing element made of glass as your source. If you could 3D print with resin, finish and polish the print by hand and then clone with optically clear resin it would open up all kinds of options. Of course, the easy response to this is “just print with clear resin!” which is potentially possible, but most “clear” printing resin tends to go yellow quite easily as they’re a bit more susceptible to UV light than two-part casting resins.
I’m definitely looking forward to the follow-up to this video!