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The importance of edges is shown.
The grey strips are shaded uniformly, but they don't seem to be uniform at all.
They are perceived as being darker on the dark side and lighter on the light side of the edge.
The eye has nerve impulse processing.
The creative founder of the Polaroid Corporation, Edwin Land, advanced a theory that takes various factors into account.
The eye-brain system can compare a candle-illuminated white table cloth with its surroundings to determine if it is white, because each retinex forms an image that is compared with the others.
An experiment done by Land shows that some type of image comparison can produce color vision.
There are two pictures taken of a scene on black-and-white film, one using a red filter and the other using a blue filter.
Resulting black-and-white slides are projected and superimposed on a screen, creating a black-and-white image as expected.
The images are superimposed on a screen after a red filter is placed in front of a slide.
The image appears to humans in full color with all the colors of the original scene.
The black-and-white and red images can be compared to create color vision.
The retinex theory is not completely accepted and color vision is not fully understood.
It's clear that color vision is much more subtle than a first look might suggest.
Use red, green, and blue light to make a rainbow.
The wavelength of a beam can be changed.
The light can be viewed as a solid beam or individual photons.
The eye can see objects large and small, but it has limitations to the smallest details it can detect.
Human desire to see beyond what is possible with the naked eye led to the use of optical instruments.
In this section, we will look at microscopes, instruments that can be used to enlarge the detail that we can't see with the naked eye.
The microscope has more than one lens or mirror.
The object for the second element is the image formed by the first element.
The object for the third element is the image of the second element.
The image is visualized by Ray tracing.
The microscope has multiple lens and mirrors.
When you switch between objectives in a standard microscope, the sample remains in focus.
Objectives are described as parfocal.
The movement of the objective lens and eyepiece provides the focusing ability.
The purpose of a microscope is to look at small objects.
Since the eye cannot focus on objects that are too close, the final enlarged image is produced in a location far enough from the observer to be easily viewed.
A compound microscope has an objective and an eyepiece.
A case 1 image is larger than the object because of the objective.
The object is the eyepiece.
A case 2 final image is further magnified by the eyepiece.
The case 1 image is larger than the object because the object is slightly farther away from the objective lens.
The object for the second lens is the first image.
The location of the eyepiece makes it possible to further enlarge the image.
The first image is closer to it than the focal length is.
The final image is even larger because the eyepiece acts as a magnifying glass.
The eye is most relaxed when viewing distant objects and can focus closer than 25 cm, so it is easy to see the inverted final image.
The thin lens equations can be generalized for any combination of mirrors.
The magnification of a multiple-element system is dependent on the individual magnifications of its elements.
Determine the magnification of an object placed 6.20mm from a compound microscope that has a 6.00mm focal length objective and a 50.0mm eyepiece.
The two objects are separated by 23.0 cm.
We need to find the magnification of the objective and the magnification of the eyepiece.
The thin lens equation is used.
The image distance is not known, but the object distance is.
Where is the focal length of the objective lens?
The object distance is the distance from the eyepiece to the first image.
This places the first image closer to the eyepiece than the focal length so that the eyepiece will form a case 2 image as shown in the figure.
We need to find the location of the final image in order to find magnification.
The magnification is large and negative, consistent with the image being large and inverted.
The image cannot be seen for a single element because it is virtual and inverted.
There is a final image to the left of the eyepiece.
The case 1 image to the right could have been formed if the eyepiece had been placed farther from the objective.
An image behind the head of a person is not appropriate for viewing on a screen.
In any multiple-element system, the procedure used to solve this example is applicable.
Each element is treated with an image that becomes the object for the next one.
The process is not more difficult than single lens or mirror.
The lenses are made of multiple elements and can be difficult to understand.
The objective lens gathers light from the specimen.
Where is the medium between the lens and specimen?
Light is gathered from a smaller focal region when the angle of acceptance increases.
An objective gives more detail than an objective.
The working distance is the distance from the front lens element of the objective to the specimen.
The closer the lens is to the specimen, the more likely it will be to break the cover slip.
The focal length of an objective lens is not the same as the working distance.
The focal length is measured from inside the barrel of the objective lens.
Microscopists can use the working distance as a reference point as it is measured from the outer lens.
As magnification increases, the working distance decreases.
The -number is used to indicate the light per unit area reaching the image plane.
The lens can be used if the acceptance angle is small.
The camera is able to gather light from a larger angle when the number decreases.
There is a trade-off.
Less light reaches the plane.
A setting that allows one to take pictures in bright sunlight is usually one.
Light needs to be focused into the fiber.
Light rays enter a fiber.
If we place a medium between the objective and the microscope cover slip, the answer is 'yes'.
Light rays going through different media provide a greater light-gathering ability and an increase in resolution.
Light rays from a specimen.
The path for air, water, and oil are shown.
The water and oil allow more rays to enter the objective.
We don't see the full extent of the sample when using a microscope.
The field of view is what we see when we use the eyepiece and objective lens.
The objective is manipulated to show other parts of the sample.
In scanning microscopy, the objective or sample is scanned electronically.
The image formed at each point is combined with a computer to create a larger area of the sample.
We rely on light to form an image when using a microscope.
The intensity of light falling on the objects needs to be increased.
Special illuminating systems are used.
If the specimen is examined by transmission, scattering or reflecting, the type of condenser that is suitable for an application will be different.
White light sources can be used.
It is important to make sure that the light does not cause the specimen to degrade.
X ray and electron microscopes provide better resolution than microscopes that only use visible light.
The basics of focusing and basic physics are the same as before.
The electron microscope requires vacuum chambers.
The ability to determine the positions of individual atoms is provided by magnifications of 50 million times.
We don't use our eyes to make images, instead we record them electronically and display them on computers.
It's not unusual to observe and save images formed by optical microscopes on computers.
Video recordings of what happens in a microscope can be made for later viewing.
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