The Physics of Photography How your camera works Chloe Kuba and Karin Oxenham

The Lens The purpose of the Lens is to collect light from the sample, and focus it on the image sensor. Digital Cameras tend to use the Convex lense.

Focal Length Focal Length:135mm Focal Length: 200mm The shorter the focal length, the greater the extent of the scene captured by the lens. On the other hand, the longer the focal length, the smaller the extent captured by the lens. If the same subject is photographed from the same distance, its apparent size will decrease as the focal length gets shorter and increase as the focal length gets longer.

Aperture Circular opening, diameter of circle determines amount of light that gets to the film. If an aperture is narrow, then highly collimated rays are admitted, resulting in a sharp focus at the image plane. If an aperture is wide, then uncollimated rays are admitted, resulting in a sharp focus only for rays with a certain focal length. This means that a wide aperture results in an image that is sharp around what the lens is focusing on and blurred otherwise.

Depth of Field Depth of Field (DOF) is the front-to-back zone of a photograph in which the image is razor sharp. As soon as an object (person, thing) falls out of this range, it begins to lose focus.

Aperture and Depth of Field The size of the aperture’s opening is measured in f-stops - one of two sets of numbers on the lens barrel (the other being the focusing distance). The f-stops work as inverse values, such that a small f/number (say f/2.8) corresponds to a larger or wider aperture size, which results in a shallow depth of field; conversely a large f/number (say f/16) results in a smaller or narrower aperture size and therefore a deeper depth of field.

The Image Sensor A silicon chip that converts light into electrons through the photoelectric effect Two types charged-coupled device (CCD) complementary metal oxide semiconductor (CMOS) Grid of thousands of photosites/pixels Thus the real image of a closer object forms further away from the lens than the real image of a distant object and the action of focusing is the moving of the lens to get the real image to fall on the film. The image formed is said to be real because the rays of lighted from the object pass through the film and inverted (upside down).

Converting Photons into Electrons Photodiodes absorb photons and convert them into electrons Electrons are stored in potential wells Electrons are converted into voltage CCD (charge shifts across) CMOS (transistors on each photosite) Each pixel ends up with an electric charge (voltage) proportional to the number of photons that hit it

Getting a Digital Image A/D converter converts charge into digital data Stored on memory card What about color?? Photodiodes only measure light intensity, not color value Bayer filter: each pixel measures one RGB value A processor estimates actual color of each pixel

Image Resolution The amount of detail that the camera can capture Higher resolution means less grainy The more pixels, the higher the resolution Examples 1216x912 - megapixel - printing 2240x1680 - 4 megapixel cameras 4064x2704 - 11.1 megapixel cameras - top- of-the-line 18 megapixels - entry-level DSLR

Sources http://www.shortcourses.com/guide/guide1-3.html http://www.olympusmicro.com/primer/digitalimaging/cm osimagesensors.html http://fstoppers.com/this-is-how-your-digital-cameras- ccd-chip-works http://electronics.howstuffworks.com/cameras- photography/digital/digital-camera2.htm http://electronics.howstuffworks.com/cameras- photography/digital/digital-camera.htm http://photographycourse.net/physics-of-depth-of-field http://www.astropix.com/HTML/I_ASTROP/HOW.HTM