Eyes, Cameras, and Light

• Eyes and cameras capture images using the properties of light.
• Key concepts are vision, lenses, reflection/refraction, imaging technologies, and images.

How Light Enters

• Eyes and cameras both operate as image-producing technologies.
• The eye is natural, while the camera is artificial.
• Light enters both through an opening, the pupil in the eye, and the aperture in the camera.
• The iris controls the pupil's size to regulate light automatically.
• Similarly, a light sensor adjusts a camera's aperture size.
• A camera's shutter is comparable to the iris and pupil, opening to allow light to strike the film or sensor.

How Light Penetrates The Interior

• Light entering the pupil is only the beginning of image formation.
• To see, light must hit the retina containing photoreceptors.
• Rods are photoreceptors sensitive to light.
• Cones are photoreceptors that detect colors.
• Rods function in low light.
• Cones need more light and detect colors.
• When light strikes the retina, photoreceptors signal the optic nerve.
• Light signals the optic nerve which the brain translates into an image.
• Similarly, in cameras, light chemically changes the light-sensitive film to form an image.

Focusing of Light

• Good vision and sharp photographs depend on a transparent lens to ensure light correctly strikes the retina or film.
• Biconvex lenses collect and direct light to a focal point.
• Eye muscles adjust the lens's shape, changing the focal distance to ensure a sharp retinal image.
• Automatic cameras adjust focal distance by moving the lens forward or backward.
• Manual cameras require manual adjustments.

Image Formation

• The retinal image is inverted, but the brain corrects it.
• In cameras, image orientation is unimportant as the film can be developed in any orientation.

Correcting vision problems with lenses

• Many people struggle to focus their eyes correctly, often due to hyperopia or myopia.
• Hyperopic individuals cannot clearly see close objects because the lens is unable to become thick enough.
• This results in the image forming behind the retina.
• Myopic individuals cannot clearly see distant objects because the lens is unable to become thin enough.
• This results in the image forming in front of the retina.
• Eyeglasses or contact lenses are commonly prescribed to correct such issues.
• Convex lenses assist those who cannot converge light sufficiently.
• Concave lenses aid those whose lenses focus light before it reaches the retina.

Laser Eye Surgery

• Laser surgery can be an option for those who prefer not to wear glasses or contact lenses.
• Surgeons use a laser to reshape the cornea.
• The transparent outer covering of the eye is also reshaped.
• Surgeons cut and fold back a thin tissue flap, then remodel the cornea with the laser.
• This newly formed cornea acts as a corrective lens.
• This enables the natural lens to focus light correctly on the retina.

Night Vision Goggles

• Eyes struggle to see even when well-focused in low-light settings.
• Night vision goggles solve this by focusing light onto an image intensifier.
• Inside the intensifier, luminous energy releases particles striking a phosphor-coated screen.
• Phosphors glow green, creating a bright green image for the wearer.

Other Eyes in the Animal Kingdom

• Camera eyes have a cornea, lens, and retina, similar to a camera.
• Camera eyes are generally round in shape.
• Most vertebrates possess camera eyes, although their eye structure can vary.
• Fish feature round lenses protruding through the pupil, allowing them to see in nearly all directions.
• Birds possess sharper vision than humans with five types of cones that are sensitive to different wavelengths, allowing them to distinguish a greater range of different colors and shades.
• Nocturnal animals like cats and owls have large pupils and a reflective layer known as the tapetum lucidum for collecting as much light as possible.
• Nocturnal animals have more rods than cones for better vision in low light.
• Invertebrates like octopuses also possess camera eyes that are similar to human eyes, but their lenses will move to focus instead of changing the shape.

Compound Eyes

• Insects and crustaceans have compound eyes made of numerous small units called ommatidia.
• Each ommatidium has a lens, a focusing cone, and a photosensitive cell that sends messages to the brain.
• The convex surface of insect eyes allows them to detect movements well, making it hard to swat a fly.
• Compound eyes struggle to form a single, coherent image.
• Compound eyes' images are a mosaic composed of tiny luminous points.
• Image clarity depends on the number of ommatidia; more ommatidia result in a more detailed image.
• Ants have relatively few ommatidia.
• Dragonflies have about 10,000 ommatidia.

Storage and Transmission of Images

• The brain plays a crucial role in visualizing scenes by sorting, storing, and retrieving image information in terms of electrical impulses down along neurons.
• Scientists do not fully understand how images are stored or why some last longer than others.
• Traditional photography, based on chemicals, can fade over time.
• Digital storage converts information into numbers, preserving it more reliably as this is how the computers can store all types of data and images.

Stadium Images

• Creating large stadium images involves each person holding a colored card.
• From afar, these cards form a large image, but up close, they look like individual colored cards.
• Each card receives an "address" based on its row and seat number to ensure organization.
• Cards are similar to the coordinates on a graph.
• Images can be correctly placed if the cards are mixed.

Digital Images

• Digital imaging functions similarly to creating a large stadium image with colored cards.
• An computer divides an image into small elements called pixels and assigns each coordinate numbers, like seat numbers in a stadium.
• The computer then converts the image into a series of numbers that can be stored.
• Computers read the coordinates and reassemble the pixels in the correct order to recreate the image.

Coloring a Digital Image

• Creating a digital image involves arranging the pixels in the correct order and assigning a color value to each pixel.
• Each value corresponds to a specific color, like the different colored cards in a stadium image.
• The computer reads each pixel’s value and displays it in the assigned color when the image is assembled.
• Values correspond to grey values for black and white images.

Digital Image Quality

• Image quality is influenced by the size of its pixels for a digital image
• Large pixels cause the image to appear as small squares, thus reducing the fine details.
• The higher the number of total pixels, the better an image becomes clearer and more detailed.
• A higher resolution equates to more pixels per light unit.

Digital Image Capture

• Scanners, digital video recorders, and cameras capture images similarly to classic cameras.
• Light enters through an opening and strikes a photosensitive surface.
• CCD photographic sensor replaces the chemical film.
• The CCD is a wire grid which produces an electrical charge when light strikes the grid.
• This charge converts electrical information into digital information.
• This electrical data can then be stored on a computer hard disk, compact disk or digital tape.

Digital Transfers

• Digital information can be transmitted far past a hard drive's limits.
• Weather satellite images are captured with digital cameras with information of electrical signals transferred back to earth.
• Camera techniques are practical as a replacement for physical film that would otherwise need to travel physically back to the earth's surface.
• Digital cameras can capture various parts of the electromagnetic spectrum beyond lighting, enabling data collection on the different planet's regions depending on electro-magnetic radiation.