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26.1 Physics of the Eye
There is a compound microscope.
Explanation of optical aberration.
The computer screen has an image on it.
One's favorite teddy bear, a picture on the wall, or the sun rising over the mountains are some of the things one cherishes.
ricate images help us understand nature and are useful for developing techniques and technologies to improve the quality of life.
The image of a red blood cell almost filling the cross-sectional area of a tiny capillary makes us wonder how blood makes it through and not get stuck.
We are able to see the structure of the viruses.
Understanding and models of physics are required to develop new techniques and instruments.
An enabling science is a science that enables development and advancement in other areas.
The advancement of major areas of biosciences can be accomplished through physics.
The enabling nature of physics is shown through an understanding of how a human eye is able to see and how we are able to use optical instruments to see beyond what is possible with the naked eye.
The eye is one of the most interesting optical instruments.
The eye is amazing in how it forms images and in the richness of detail it can detect.
To reach what is called "normal" vision, our eyes need some correction, but should be called ideal rather than normal.
Common vision correction and image formation by our eyes are easy to analyze.
The eye is shown in figure 26.2.
A single thin lens is formed by the cornea and lens.
For clear vision, a real image must be projected onto the light-sensitive retina, which lies at a fixed distance from the lens.
The power of the eye's lens is adjusted to produce an image on the retina at different distances.
The fovea has the greatest density of light receptors and the greatest acuity in the visual field, which makes it the center of the image.
The eye can detect light intensities from the lowest observable to times greater with the help of the variable opening and chemical adaptation.
This is a huge range of detection.
Sense direction, movement, sophisticated colors, and distance are some of the functions our eyes perform.
The processing of visual nerve impulses begins in the eye and continues in the brain.
The eye sends signals to the brain.
The eye's lens and cornea act together to form a real image on the light-sensitive retina, which has its densest concentration of receptors in the fovea and a blind spot over the nerve.
The power of the eye's lens can be adjusted to provide an image on the retina for different distances.
There are layers of tissues in the picture.
They have not been included in other pictures for clarity.
Refractive indices are important to image formation.
Refractive indices are relevant to the eye.
The biggest change in the Refractive index is at the eye.
The rays bend according to the.
The power of the eye is provided by the fact that the speed of light travels from air into the cornea.
The remaining power is provided by the lens.
Even though the light rays pass through several layers of material, the lens can be treated as a single thin lens.
The image is similar to the one produced by a single lens.
There is a case 1 image.
The brain makes inverted images seem upright when they are formed in the eye.
An image is formed on the eye's surface with light rays coming in and out of the lens.
The inverted real image is created by the rays from the top and bottom of the object.
The distance is smaller than scale.
The image must fall on the retina in order to produce clear vision.
The image distance must be the same for all objects because the lens-to-retina distance does not change.
The eye adjusts the power and focal length of the lens to fit objects at different distances.
A person with normal vision can see objects up to 25 cm away.
The near point is the shortest distance at which a sharp focus can be obtained and we will consider it to be 25 cm in our treatment here.
The eye is shown in Figure 26.4 for distant and near vision.
Since light rays from a nearby object can enter the eye, the lens must be more powerful for close vision.
The action of the ciliary muscle surrounding the lens makes it thicker.
One reason that microscopes and telescopes are designed to produce distant images is that the eye is most relaxed when viewing distant objects.
Vision of very distant objects is called totally relaxed, while close vision is accommodated, with the closest vision being fully accommodated.
It was possible to see distant and close objects.
If they were parallel, a more powerful lens was needed to converge them on the retina.
The thin lens equations will be used to examine image formation.
Normal vision can be obtained if the lens-to-retina distance is equal.
Estimate the diameter of the eye.
Considering how small the image is on the retina, the eye can detect an impressive amount of detail.
The following example shows how small an image can be.
Take the distance from the lens to thetina.
The height of the object is cm, so we want to find the height of the image.
The object is 60.0 cm away.
The image distance has to be equal to the lens-to-retina distance.
The equation can be used to find something.
The limit to visual acuity is even smaller than this, which is why this is not the smallest image.
Limitations on visual acuity have to do with the wave properties of light and will be discussed in the next chapter.
The brain and eye have inherent limitations due to them.
The power of the eye is calculated by assuming a lens-to-retina distance of 2.00 cm.
The image must be on the right side of the eye.
As discussed earlier, for distant vision and for close vision.
The equation written above can be used to solve both cases.
All distances should be expressed in meters because power has units of diopters.
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