Thursday, July 16, 2009

Experimenting with a "liquid lens"

A couple months ago, I started to investigate building an auto-focus mechanism for cameras that could operate in high magnetic fields. This was for a work project (where I build MRI-compatible devices). Inside an MRI machine, the base magnetic field is usually 1.5 or 3 Tesla. At these fields, any motor or solenoid that relies on manipulating a local magnetic field will not work. Unfortunately, manipulating magnetic fields is one of the easiest ways to convert electricity into physical movement, so most auto-focus assemblies are built this way. There are some
alternatives, though:

Piezo "ultrasonic" ring motors. Many high-end DSLR (and SLR) lenses have silent ring motors that vibrate at ultrasonic frequencies to create rotation. Great! The only problem is that they are built from steel, and the steel cannot be used in the MRI environment. They are also too big -- I need a tiny lens about 1/4" in diameter, not 2" like a DSLR lens

Piezo wiggler motors. Looks interesting, but getting a sample is near impossible. The screw assembly is probably steel, and the system requires a fairly rigid and complex slide system

Liquid lenses. These lenses are built by sealing a small amount of water and oil inside a shirt button-shaped capsule. The walls of the capsule are metal with glass windows on the faces of the button. The water and oil will not mix, and the boundary between the fluids will bend light because the two liquids have different refractive indices. If the walls of the capsule are charged with electrical current, the shape of the water droplet will change because of electrostatic attraction. (check this out: ) The oil is made up of non-polar molecules, so it does not share this same attraction. By controlling the voltage on the capsule walls, the shape of the water can be controlled and thus the focal length of the lens formed by the water-oil interface. Neat!

The liquid lens is the metallic button-shaped thing on the left. I built a holder for the lens out of 1" squares of copper clad board.

There are only one or two manufacturers of liquid lenses: Varioptic, Philips, and maybe Siemens. Philips and Siemens would not discuss the liquid lens and would not sell any samples. Varioptic would send samples -- only $340 for each lens! What?! The evaluation kit was a mere $4000, while the full developer's kit was $12,750. I kid you not. What kind of company would charge a potential customer $12k for the privilege of testing their products? Insane!

Anyway, since I couldn't deal with any of the manufacturers directly, I set about finding an off-the-shelf product that contained a liquid lens. After many hours of searching, I found an actual product that had the Varioptic lens in it: Digitus DA-70817. There were many other prototypes and press releases for other liquid lens products, but it seems the Digitus camera is the only mass-produced device right now. Unfortunately, it is not available in the USA. It's not on eBay. has it, but will not ship to the USA. After many more hours of searching, I got in touch with a German distribution company called Assmann (no joke). I exchanged a few emails with a friendly person there, and she sent me five of these cameras (about 25 euro apiece with the usual outrageous international shipping charge).

I removed the lens from one of the cameras and mounted it between two pieces of copper clad board. To make the lens change focal length, I need to supply 0-70V AC to the lens. AC is required to prevent the liquid in the lens from polarizing over time and losing effectiveness. The voltage needs to be fairly high to deform the water drop sufficiently, and also needs to be changed rapidly for quick changes in focal length. Fortunately, there are two companies that make ICs specifically designed to directly drive liquid lenses. Unfortunately, one of the companies, Maxim, will not sell samples of their chip, and they will not even give out datasheets for it. Take a look: How rude is that? WTF?! The other company that makes liquid lens drivers is Supertex. They will sell samples of their HV892 at a reasonable price, but the chip is only made in a 10-lead 4mm x 4mm DFN package with .65mm pitch. Apparently, this SMD footprint is so unusual, there are no DIP converters available from anywhere. Geeeez! I ended up designing my own PCB for the chip and having them made at Here it is:

I interfaced the chip to an Arduino Duemilanove. The Arduino sends a value between 1 and 255 to the HV892 via the I2C bus. The value controls the HV892 output voltage, and hence the lens's focal length. I am not sure what the mathematical relationship is

I used a laser pointer to show the different focal lengths that the lens can achieve.


  1. I couldn't even get a response from varioptic regarding price of developers kit (damn French!) Thanks for the information.

  2. I like it. I have experimented with electrowetting (EWOD) as well, using a USB Microchip board (UBW). Similar method to liquid lenses, although EWOD attempts to move droplets around the surface of a board, mix with each other, etc.

    It should be possible to drive the liquid lens directly (i.e, without/replacing the proprietary driver IC such as the Supertex), as follows: use high voltage solid state relay, an AC supply which supplies ~60-90VAC at 1kHz at under 1mA, and a microcontroller with GPIO or PWM to control the relays. Play with the PWM control until the liquid lens starts to actuate. It's a project in itself, of course.

    By the way the product brief PDF for the MAX14515 can be found with some searching, which shows it drives ~42VRMS max @ 1kHz min to the lens. Any standard motor control circuit could do the same (just make sure the A/C supply is current limited to ~1mA max). Using a "digital resistor" might allow simple varying of the voltage in a custom circuit.


  3. Cool! Were you experimenting with the electrowetting for a business application or just as a hobby?

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  5. > What kind of company would charge a potential customer $12k for the privilege of testing their products?

    Any company that can! They've probably figured out that a customer that needs this kit can't get it from anywhere else. At least not much cheaper than that.

  6. Hi Ben, there is a online shop that offers a dev-kit for 990 euro. At least the price is reduced by one order of magnitude...

  7. Hi Ben,

    I am experimenting with electrowetting and I would like to reproduce your design.
    Could you please share the PCB file of the ExpresPCB design?

    Thank you,


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  9. Hello Ben,

    We are two students, and we want to reproduce your system to exploit a liquid lens.
    We were wondering whether you could share the PCB file of the ExpressPCB design.

    Thank you,

    Pierre-Luc and Loïc