Sue Hubbard in The New Statesman:
The camera obscura (Latin for a darkened room) is an optical device that projects an image of its surroundings onto a screen and was one of the inventions that led to photography. Consisting of a box or room with a hole in one side, light from an external scene passes through the hole and strikes a surface inside where it is reproduced, upside-down, but with colour and perspective preserved.
To come across Anish Kapoor's startlingly beautiful C-Curve sculpture in the middle of Kensington Gardens is to experience the effects of the camera obscura but without the darkened room. Walk towards the highly polished concave surface of stainless steel and the surrounding lawns, autumn trees and people will appear upside down like a child's vision of Australia, where everything is topsy-turvy. Move around to the bulging convex facade and the world will be the right way up again.
Clouds, dog-walkers, babies and bikers all pass across the silver screen in a filmic version of real life. The players in this pageant stroll on and off stage passing, only for a moment, like the shadows in Plato's cave. “Life's but a walking shadow, a poor player, That struts and frets his hour upon the stage, And then is heard no more,” Macbeth despaired. What is real? What is a chimera? asks Kapoor in these mirroring multiplications and inversions of our surroundings, which pose questions about our very existence.
From the first encounter with these four stainless steel structures placed within Kensington Gardens, we are reminded that the world is rarely what it seems. As Alice discovered in the looking glass, reality is a slippery concept. The symbolism of the mirror is ancient; from Narcissus to Snow White, it is an image that has caught the human imagination.
Also see here