How camera lenses are made

A camera lens is a stack of many glass elements, because no single curved piece of glass focuses cleanly.

stations: 6
things upstream: 35
raw sources: 10
steps from the ground: 8

The short version

A camera lens is a compound lens made up of many glass elements, because one simple lens cannot cancel the distortions that arise. Glass blanks are heated, pressed to a rough shape, then ground and polished to a curve. Elements get thin coatings, are centered in a metal barrel with the aperture, and are tested.

Melt the optical glass

Sand and chemical additives are melted into optical glass with a carefully chosen refractive index. Different glass types bend different colors by different amounts, and designers combine them to cancel color fringes.

Goes in
Silica sand
Press the glass blanks

Softened glass is pressed to a rough lens shape in a mold. Some aspheric surfaces are molded straight to their final curve.
Grind and polish the curve

Each blank is ground and polished with pads carrying hard grains, swapped several times for ever finer grit. The work usually takes hours, and the finer the finish wanted, the longer it runs.
Coat the surfaces

In a vacuum chamber, thin layers of material are laid down on each surface to cut reflections. Without coatings, light bouncing between the many surfaces would wash out contrast.
Center and cement the elements

Elements are aligned in groups on their optical axes and sometimes cemented together in pairs. Misalignment can blur one side of the picture.

Goes in
Adhesive
Mount in the barrel

The groups go into a barrel of machined aluminum or molded plastic along with the aperture blades and focus motor. Each lens is measured on a test bench before it leaves.

Goes in
Aluminum Polycarbonate

End of the lineCamera lens Next it goes into digital camera.

Worth repeating

Polishing a lens can take hours, while molding presses a heated glass preform to shape in hot tooling.
Diamond turning, used for complex shapes, needs no polishing afterward.