Nokia 808 PureView: How to make the perfect Carl Zeiss lens

March 09, 2012

The size of the Carl Zeiss lens for the new Nokia 808 PureView is smaller than a sugar cube, and the lens for a Nokia Lumia 800 is only slightly bigger than a pin – but both produce images as sharp as a ZEISS lens used on a professional photographic camera.

Dr Hubert Nasse is the Senior Scientist at Carl Zeiss Camera Lens Division, and tests lenses rigorously in the ZEISS labs. He loves lenses.

“I spend my working life testing lenses to the very highest scientific standards,” he says. “And of course that is how you accurately judge that a lens meets ZEISS specifications. But there is more to a lens than that – when you work with lenses every day, you appreciate their true craftsmanship. A ZEISS lens even has a certain smell – to me it smells professional.”

Nasse fits the lens from a Nokia Lumia in the Carl Zeiss K8 measuring machine – which takes up most of the side of one room. He makes a few adjustments and the meters shoot up.

Then he fits a professional lens in the machine and adjusts the parameters,
“Now watch these meters,” The three meters, which measure different sharpness parameters, shoot up to over 90% over 80% and over 70%. The higher the number, the sharper the lens. This time the professional lens has registered as lower than for the Lumia lens.

Nasse sits back with satisfaction: “That’s how good these lenses for mobile phones are.”

So how can two lenses that appear so different produce the same image quality?

“The formal optical parameters are about the same,” Nasse says, but there are key differences.

This comparison between the absolute performance of a 2/50mm photographic lens for full-frame (24×36mm) sensors and a 2.4/8mm lens for a mobile phone shows that the lens for the mobile phone is sharper. However, an image taken with the big lens is better overall because the information is not compressed on such a small image area as it is on a mobile phone sensor.

Traditional camera lenses are made from a piece of glass called a ‘blank’, and then polished with a computer controlled precision tool. Lenses used in mobile phones are made from plastic and pressed in a hold.

“The only reason you can’t make a larger camera lens from plastic is the physical size. A larger plastic surface area expands and shrinks too much at different temperatures, but that doesn’t apply on a lens as small as one fitted in a mobile phone.”

Plastic gives mobile phone lenses one distinct advantage – a dimple.

Christian Bannert, the head of R&D at Carl Zeiss Camera Lens Division draws some diagrams on the whiteboard: “Glass can only be made in spherical shapes and to a certain extent pressed or polished to aspherical shape, but there are big problems with the way that it refracts light as soon as it comes to compact wide angle lenses like in camera phones,”

Extreme aspheric lenses – that seem dimpled – are much better at refracting light in this case.

Back in the lab Hubert Nasse explains the other ways that camera lens and mobile lenses vary: “There are two main differences – the size of the sensor, and the distance between the sensor and the surface of the lens. In mobile phone optics the sensor is much closer to the lens.”

While phone designers want phones that are sleek and slim, optics designers crave space: “You need some volume, optical designers always want more space…making a lens in a narrow space is highly demanding.”

The Research and Development Project Manager for Mobile Phones, Oliver Schindelbeck, is watching the lens test. He agrees: “The struggle of the past years is making cameras smaller and smaller, but getting more megapixels and increasing the image quality.”

Decreasing the size of the camera and lens increases the sensitivity of the system, and makes production more challenging:

“We’ve made tremendous progress…now we have really good image quality with cameras below 7mm in height and that’s impressive.”

Schindelbeck has worked on some notable milestones in the partnership between Nokia and Carl Zeiss:

“The first model we made with Nokia was the N90, and it was crucial in breaking the 2 megapixels mark. For Carl Zeiss this is the minimum sensor resolution in order to transport good Carl Zeiss image quality. Below that the resolution is too low to have benefits from a high quality lens”

As for the Nokia N8. Well, this is team that still goes into raptures over making the lens for the N8.

If there is one misunderstanding that they are all desperate to dispel, it is the myth of the megapixel. Fewer than 2 megapixels really affects image quality, but bigger than that is not necessarily better. Paper prints or PC-displays usually do not need a much higher resolution.

“Reducing the performance of a camera down to one number does not give you a true reflection of a camera,” says Oliver Schindelbeck. “It is wrong to say 8 megapixels are better than 5 megapixels. That tells you nothing about colour shading, or noise reduction – or any of the other things that really matter.” Human eyesight doesn’t focus just on resolution, he adds – it’s much more.

The team at Carl Zeiss works with Nokia to design and develop the lens, and then oversees the manufacturing process – monitoring the accuracy of the machines that make them and the final lenses in each type of phone. Strict accuracy is essential.

“We work together with Nokia from the first idea; we look at optical design, calculating the lens system, discussing the limits of lens itself and the specifications for quality. Then we qualify the suppliers to make sure they meet our necessary standards. We test the quality robustness and image processing of the first prototype – and then we test the final prototype and do any fine tuning.”

This is a team who take the Carl Zeiss brand seriously – at some points in the afternoon they try out their Nokia Lumia phones under the table, explaining that they take lots of images to see how they perform in low light and real life situations.

Oliver Schindelbeck says that it’s no secret that there are manufacturers all over the world who can cut and polish a lens, or make a component, but: “It’s only when we’ve taken all of those steps, and ensured our standard of quality at every stage of the process, that we are happy to say – this is a Carl Zeiss lens.”

Back in the lab Hubert Nasse demonstrates what making a perfect Carl Zeiss lens means when he hefts a large cinematography lens off the table. The walls of the corridor are lined with posters of famous films shot with this very piece of equipment – including Lord of the Rings, and The King’s Speech.

He points out the cold feel of the aluminium body, the weight, and the deep engravings that mean measurements can be read almost in the dark. Next to it he holds up a Nokia PureView 808 lens – the size of a sugar cube. “It’s the knowledge transfer between these two lenses,” he sighs “Perfect synergy.”

This article was written for Conversations by Nokia and Republic Publishing

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