Week 12: Optical Instrumentation Flashcards
Human eye is comparable to the design of a photo camera name the comparability of these below: iris, cornea & lens, retina, brain
Iris = aperture stop
Cornea & lens = objective lens
Retina = photo sensor
Brain = image processing computer with algorithms
In contrast to a photo camera….
- The eye is not centred at a common axis
- Performance of the ‘light sensors’ are different
-The resolution of the camera’s detector is higher in the central retina than the peripheral retina
Describe Entrance & Exit Pupils
- Cornea forms an image of the pupil (aperture stop)
- Exit pupil of the eye is the image of the same aperture stop formed by the lens;
- E is the centre of the entrance pupil and E’ is the centre of the exit pupil
- Marginal ray passes through the edge of the lens
- Chief ray passes through the centre of the aperture stop (pupil)
Describe Visual axis
The line between the fixated point 01 and fovea by nodal points N and N’
Describe Nodal ray
The angle to the ray’s incident on the optical axis is equal to the angle to the refracted part
Describe Object & image distances
Are measured from primary & secondary principal planes
Describe Cross section of the primary & secondary plane
At the optical axis are called Primary (P) and secondary (P’) principal points
Describe Line of sight
Line between the fixated point 01 & centre of entrance pupil E
Describe Pupillary axis
Line passing thorough entrance pupil & perpendicular to the corneal surface
Describe Optical axis
Line connecting centre of refracting/reflecting surfaces, cornea, pupil, lens, retina
Describe Kappa k
Angle between the optical and visual axis, usually 5°
Describe Fixation axis
The reference axis for eye movements, determined by object point 01 & centre of eye rotation (C)
Describe how speed cameras operate briefly
- Detect the speed of vehicles by using piezo electronic detectors embedded into the road surface or RADAR & LASER technology
- The piezo detectors deflect slightly when a vehicle is driven over the detectors, which then triggers an electronic device that accurately measures the speed of the vehicle
Describe Fixed Speed Cameras
- Fixed speed cameras can monitor 1 to 4 lanes in the same direction
- The original recorded images are stored electronically on a WORM (Write Once Read Many) disk, which cannot be overwritten or altered
What is Gatsometer Digital Rader Camera System – Parabolic (DRCS-P)?
- RADAR technology is used to measure how fast a vehicle is travelling & to trigger the camera into act
- If a vehicle is driving above the road speed limit then two photos are taken in quick succession
- It is a legal requirement to have a secondary measurement for speed
Describe Photocells / Photoelectric Cells briefly
- They are also known as CdS cells or light-dependent resistors (LDR) or photoresistors
- Photocells are sensors that detect light
- They are small, inexpensive, low-power, easy to use and do not wear out
- Photocells are resistors that change their resistive value depending on how much light is shinning onto the squiggly face
Photocells are useful for most light-sensitive appliances to detect…
- Is it light or dark?
- Is there something in front of the sensor (that would block light)?
- Is there something interrupting a LASER beam (break beam sensors)?
List the Photo-Cells Types
- Photoconductive
- Photovoltaic
- Photoemissive
Briefly describe Photoconductive
- The front surface has a lens on top & the back has light-sensitive materials made of calcium sulfide with a snake-pattern of electrical connection running across it
- In darkness or normal light, the LDR have high resistance but when light is shone the resistance decrease dramatically by converting incoming light into electrical energy
Briefly describe Photovoltaic
- These are like diodes, made from two layers of semiconductors placed on top of another
- The top layer is electron rich & bottom layer is electron poor
- When the light is shone on top, electrons leap up from the bottom layer to top, making a voltage that can drive through external circuit providing the solar power
Describe Photoemissive
- Are oldest way of turning light into electricity
- They are sealed glass vacuum tubes inside which there is a large metal plate that serves as negative terminal with a smaller, positively charged, rod-like terminal running inside it
Explain Fibre-Optics
- Used to transmit data, voice & images by the passage of light through thin, transparent fibers
- Also a basis of the fiberscopes used in examining internal parts of the body or inspecting the interiors of manufactured structural products
- The basic medium of fiber optics is a hair-thin fiber made of plastic but often glass
- First data from a device is converted from electrical information to series of light pulses using LASER. Then, the LASER is fired to the fiber-optic cable
- Photoelectrical cells turn the pulses of light back into electrical information
- Light travels via a fiber-optic cable by bouncing repeatedly off the walls
Describe flat-screen/LCDs
- Liquid–Crystal Displays (LCDs) use same technology as calculators, cell phones & digital watches
- In 1888, Fridrich Reinitzer discovered liquid crystals
- Picture is made from millions of tiny blocks called pixels
- Each one of these is effectively a separate red, blue or green light that can be switched on or off very rapidly to make moving colour picture
- Pixels are switched on or off electronically using liquid crystals to rotate polarised light
How about LED displays?
- LEDS uses Light-Emitting Diodes for backlights instead of fluorescent
- LEDs usually have better picture quality
