Mar 13 2020

Extreme Depth of Focus Lens

This is definitely one of those “Holy Sh*!” technology breakthroughs; a game-changer that will likely have many more implications than you can take in immediately. Researchers have demonstrated that with the “judicious design of a multi-level diffractive lens (MDL)” they can create a single flat (one thousandth of an inch thick) thin lens with an extreme depth of focus – four orders of magnitude greater than traditional lenses. Let that sink in.

The depth of focus (or depth of field for objects not at infinity) is the range over which objects are in focus. You can adjust the depth of field on a camera by changing the aperture, with smaller aperture settings having a deeper depth of field. But you still need to focus the camera to bring the desired image into sharp focus. This requires that the camera can change the distance between the lens and the sensor, and modern cameras may use multiple lenses. Good cameras also use multiple lenses for different colors (wavelengths of visible light) to make sure all the colors are focusing the same way.

Now imagine if all this could be replaced with a single very thin flat lens. That is what the researchers have done. They accomplish this by using nanostructures on the glass to control the path of the light. The lens can simultaneously focus objects at different distances, and also light of different colors. What we have now is a proof of concept, and of course we need to see what an an actual commercial camera using this technology will be like. But if the published results pan out, there are several immediately obvious implications.

The first is much smaller, cheaper, lighter camera lenses. This will be great for cell phones and other tiny electronic devices with cameras. Medical devices such as those used for endoscopic surgery would also benefit from smaller lenses. Any situation where size and weight are at a premium would benefit – such as drone cameras.

But always the most interesting applications of such new technology is not just making existing applications better or cheaper, but the entirely new applications that open up. Similar to when LED lighting became practical, they not only replaced other existing lighting, we started to see LED lights in places where they were never before practical. My favorite example is the little light at the end of the power adapter for my laptop. When it has power, the light is on, which is very helpful conformation that it is adequately plugged in and the outlet and/or power strip has power. This is something I never knew I couldn’t live without until LED lighting came along.

So what are going to be the new applications made possible by this super small lens? I don’t know, but here is one question I have. (Science or fiction spoiler ahead for those who have not yet listened to this week’s SGU episode.) On the current episode of the SGU the fiction item was a new contact lens that could automatically focus at a wide range of distances. Forget bifocal or even trifocal lenses. I actually have separate reading glasses for computer distance and close up (smart phone or book) distance. Imagine a pair of contact lenses that would keep everything in focus. That was the fiction, because it doesn’t exist yet. So I was particularly amazed to see this news item.

The ability to keep a wide range of distances simultaneously in focus with a single very thin lens certainly makes contact lenses with this ability seem feasible. It remains to be seen if this technology will work in the shape of a contact lens. But if not, then I would settle for a single pair of glasses that keeps all functional distances in focus, from close reading to the computer screen or television, to all people and objects in a typical room. You may only need to take them off for extreme distance. This same technology might also be applicable to color enhancement, filtering out UV and unwanted glare, and even correcting for some types of color blindness.

But probably the most exciting application is the one I have not even dreamed of yet. With the combination of a tiny lens like this, and the super tiny CCD chips possible, we can put a functional camera almost anywhere. Of course, this can also be a bad thing. Surveillance cameras can be virtually invisible with this tech. But that’s always the way with great technological breakthroughs, there are useful applications that will make our lives better in some way, and then dubious applications that will be used for bad purposes. We have to take the good with the bad, and mitigate the bad in other ways.

In any case, I would be surprised if this technology does not start showing up in everyday devices in a few years (unless I’m missing something or the reporting is ignoring a fatal flaw, which does happen).

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