How Are Mirror Lenses Different From Other Camera Lenses

Applications of Mirrors and Lenses

We take a cursory await at some ways in which mirrors and lenses are utilised in engineering science.

The Homo Eye and Corrective Lenses

A greatly simplified view of the human middle is shown beneath. The pupil is a little hole which allows low-cal to pass into the eye. Backside the pupil lies the eye's lens. Muscles in the centre command the size of the pupil and the shape of the lens, thereby adjusting the amount of light that enters they eye and the focus of the lens. The retina is a sensitive layer of nerves at the back of the eyeball; incident light upon the retina is translated into a coherent paradigm past the encephalon.

$The eye and eyeglasses.$

Many people do not have perfect vision; that is, a lot of people accept eyes whose lenses do not focus light properly on the retina. Two well-known vision bug correctible via eyeglasses are nearsightedness (motion picture (a) to a higher place) and farsightedness (moving-picture show (c)). Nearsightedness focusses rays of light in front of the retina, while farsightedness focusses rays behind the retina. A diverging lens can correct nearsightedness by bending incoming light rays outwards, so that the eye's lens (which usually bends incoming rays also much) focusses the light closer to the retina (picture (b)). A converging lens similarly corrects farsightedness (picture (d))¹.

Magnifying Spectacles

In our study of lenses, we saw that if the source was placed inside a focal length of a converging lens, the lens yielded a magnified image on the same side of the lens as the source. This is, of class, the detective's best friend, the magnifying drinking glass.

$A magnifying glass.$

The corporeality of magnification, as we know from our handling of lenses, depends on the distance of the source from the lens, and the refractive index of the lens material.

Cameras

Cameras, unsurprisingly, work on similar principles as the centre.

$A simple camera.$

The discontinuity, which lets light into the inside of the camera, corresponds to the student. The system of lenses in a camera performs the same function as the lens of the eye. Yet, whereas the lens of the center changes shape to change focus, glass lenses are not very forgiving of shape changes. Instead, the lens system can exist slid along its optical axis in order to focus on the film. Of form, the film plays the role of the retina. In improver, cameras have a shutter, which opens and closes quickly then that the film does not get inundated with lite. This produces a more or less clear paradigm of the instant that the lensman shoots.

Microscopes

Elementary microscopes use lens systems to magnify very small objects, every bit illustrated in the following diagram.

$A simple microscope.$

An object (S ₁) also small to examine with the naked middle is placed just outside the focus F_o of the objective lens in the microscope above. Tracing the infinite and central rays as we have before, we can find the location of the paradigm I ₁. Nosotros know that a source within the focal length of a converging lens will upshot in an enlarged virtual image; hence if nosotros position the eyepiece of the microscope so that its focus overreaches I ₁, the final image seen (I _ii) will be a magnified image.

The shrewd reader will notice that our simple microscope gives an inverted prototype, which could be inconvenient for certain situations. This trouble can be solved by using a different lens system, as shown beneath.

$A microscope giving an upright image.$

The colouring above is meant to assistance the reader to identify which components the labellings refer to. Our microscope consists of iii converging lenses. From our pictorial treatment of lenses, we know that a source between one and two focal lengths of a converging lens gives a magnified and inverted prototype. Thus, nosotros put the source somewhere within this magic region for Lens A, and figure out where the image will state using ray tracing. Knowing where the first epitome lands, nosotros identify a second converging lens, B, so that the offset image falls between 1 and two focal lengths for Lens B. Finally, nosotros tin utilise ray tracing to discover the position of the second image. Subsequently interacting with lens B, the source point has been magnified twice, and inverted twice, then it is upright. Nosotros place Lens C so that the 2d image falls within one focal length of C. As we know, such an arrangement will produce a magnified, upright, virtual image, as illustrated.

Telescopes

Telescopes serve much the same purpose every bit microscopes; both magnify what the user wishes to observe. The divergence is that microscopes are supposed to be used to examine small objects that are close to the objective lens, while telescopes are supposed to be used to examine objects that are very far away (in many cases, actress-terrestrial). For historical purposes, we include a diagram of Galileo'due south telescope here.

$Diagram of Galileo's telescope.$

J is the image point that would have been seen had the diverging eyepiece not been inserted betwixt the objective lens and J. The image bespeak I is actually seen when 1 peers through the eyepiece.

Of course, just like with microscopes, much more complicated lens systems can be utilised, resulting in greater magnification, and thus finer detail.

Data Storage Media

All of the applications we have looked at and so far are dominated by the refractive half of our axioms of optics. This might lead to the unwarranted conclusion that reflection plays little or no role at all in technology. In the next and last leg of our journey together in optics, we will have reason to mention the reflecting telescope, which uses mirrors to focus light from far away objects for study. Hither, nosotros consider CDs.

Without straying too far into the milieu of informatics, nosotros can say that all a computer actually understands is 0s and 1s. The Law of Reflection gives a relatively easy way of storing and reading these digits.

$Inner workings of a CD reading device.$

A CD is basically a highly reflective surface that is filled with bumps and valleys. A light amplification by stimulated emission of radiation is placed somewhere in the thespian's casing, and a device capable of detecting a light source is placed then that the light amplification by stimulated emission of radiation's rays will exist reflected into the device when the laser is aimed at a valley. The peaks are arranged and then that the laser'southward rays reflecting off the peaks will miss the detector completely. The detector registers 0s and 1s accordingly, when it detects the absence or presence of calorie-free.

The lens and detector are allowed to move radially, whereas the CD is allowed to spin. This offers a momentous comeback over record devices for sound, and floppy disks for computer storage. Audio tapes are sequential admission devices; data in the centre cannot exist accessed direct, instead the intervening information from the beginning to the point of involvement must be "fast-forwarded." This can exist a very slow process. CDs (which could also be thought of every bit sequential access devices, in a fashion) accept a lot of freedom in the sense that their spin and the move of the lens-detector system allows very quick admission to data anywhere on the disc. Floppy disks are magnetic media; as such they must be kept away from magnetic fields if the data they contain are to maintain integrity. CDs, as optical media, do not endure such a limitation.

The size of the peaks and valleys of optical media dictate the storage capacity -- smaller shapes ways more than data tin fit on the disc. While the trouble of minimising the size of the peaks and valleys is a manufacturing trouble, ironically, we are not complimentary of eyes. Lasers are generally the only instruments that are fine enough to chisel the microscopic shapes accurately.

<< Summary of mirrors and lenses
Complications in optical systems >>
Open carte in split window