Nokia 808 PureView lens

What's the toughest challenge in making a camera phone lens?
To achieve high resolution, when compared to regular camera lenses, while keeping the size of the lens and the camera as small as possible at the same time.

Thinness is a crucial success factor for cameraphones.
Only really outstanding cameras like the one in the Nokia 808 PureView may be a few more millimeters larger.

It is not possible to build lenses with a higher resolution than permitted by the diffraction limit.

The lens in the Nokia 808 PureView is close to the diffraction limit, a physical law that limits the resolution of a lens.

Nokia 808 lens
Strange mathematical aspherical curves, impossible in glass DSLR lenses which must be ground

One needs extraordinary resolution for the massive 41 megapixels of the sensor to be able to capture the fine photographic details.

Glass can only be made in spherical shapes and to a certain extent polished to aspherical shape,
but there are big problems with how it refracts light as soon as it comes to
compact wide angle lenses like those in camera phones

~Christian Bannert -- head of R&D at Carl Zeiss AG, Camera Lens Div.

Extreme aspheric lenses ( mathematical profile appears dimpled ) are much better at refracting light in this case.

What's so good about the Nokia PureView 808 lens?
This wonder lens achieves a resolution, which is 75% of the diffraction limit.
The only way it could be even better would be, if the f-stop number were smaller, which would mean a larger diameter aperture.
If it contained an iris to be stopped down it would only get worse, different from normal photographic lenses.
Achieving this resolution in an affordable mass market product was Zeiss's greatest challenge.

What difference do you see in a picture taken with a Carl Zeiss lens, compared to other lenses?

High and even sharpness over the whole image area. No blurred zones, no excessive lens-flare. Good control of internal reflections is important to preserve the natural colours and high fidelity images, even matching the quality of much larger digital still cameras, unless the image is enlarged excessively.

A comparison between the absolute performance of a Carl Zeiss 50mm/f2 glass photographic lens for full-frame (24x36mm) sensors
and a 8mm/f2.4 plastic lens for a mobile phone shows that the mobile phone lens is sharper.

Nokia 808 lens
Carl Zeiss Lens of the Nokia 808 Pureview

Nokia Lumia 800 lens
Carl Zeiss Lens of the Nokia Lumia 800

Nokia 808 lens
Dr. Hubet Nasse is Staff Scientist at Carl Zeiss. He demonstrates what making a perfect Carl Zeiss lens means.
He hefts a large Carl Zeiss cine lens off the table, explaining how a phone lens differs.

Nokia phone lenses
Each of the grey plastic containers hold 40 plastic phone lenses.

The image taken with the big lens is better overall because the information is not concentrated into such a small image area as it is on a mobile phone sensor.

Making a camera phone lens, takes knowledge of modern optical design, very complex mathematical lens shapes, lens molding and mounting techniques.
Many, many measurement tools are used for quality assurance.

Carl Zeiss, measure the modulation transfer function (MTF) of their lenses as a figure of merit, while checking the Image Quality of their lenses.

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 moulded to precise computed surfaces.

Why can't they make plastic lenses for larger cameras?
Physical size! A larger plastic surface area expands and shrinks too much at different temperatures.
This doesn't apply to the tiny lens meant for a mobile phone.