Modern cameras, even high-end DSLRs, are physically nothing more than an advanced version of the camera obscura. Even the ancient Greeks were familiar with this optical gadget. The term “camera obscura” can be traced back to its Latin roots and essentially means “dark chamber”, which already sufficiently explains its functional principle: When light from an object passes through a small hole into a dark chamber, a projection of the object is visible on the rear wall. This is made possible by concentrating the light rays that come from the object, whereby the image on the rear wall of the box is reproduced not only upside down but also back to front. The human eye works according to the same principle: The eyeball is the dark chamber, the pupil is the small hole and the retina is the rear wall. However, the image in its normal form is initially out of focus, which is why in nature the highly flexible lens located behind the pupil developed as part of the process of evolution: This concentrates the light, enabling the image to be focussed and thus providing humans with sharp vision. Incidentally, the optical signals received by humans are still inverted on the retina – infants see everything "back to front" although this is quickly corrected by the brain.
In the case of the camera obscura and not least every other camera, a sharp image is only achieved once a glass lens has been fitted to concentrate the light rays. The higher the quality of this optical system, the more brilliant the reproduced image will be.
To achieve precise focussing and a maximum level of sharpness, either the camera or the subject must be moved to ensure the subject is positioned at the focal point of the lens, which in turn depends on the focal length of the lens. While the lens in the human eye is flexible and can have its focal point moved independently through muscle power, a camera obscura requires a lens that can slide along the longitudinal axis – a modern camera lens. If we now simply exchange the rear wall of the camera obscura for a film or an image sensor, we find we have a simple camera. And if we take a moment to consider this principle and the quality of a standard image achieved today, it soon becomes clear what great advances have since been made that can now be found in every camera and also in every single lens.
Functional principle of a simple camera (camera obscura). A glass lens increases the quality of the reproduced image. A high-quality lens, consisting of a complex lens system, makes it possible to take brilliant photographs.
Illustration: Fouad A. Saad/Shutterstock.com
