What are Optical Instruments?

An optical instrument is a device that processes light waves, either to enhance an image for just viewing purposes or to analyse and determine its whole characteristic properties. Commonly used examples of optical instruments include periscopes, microscopes, telescopes, and cameras. Optics is also one of the branches of physics that observe and study the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. The term optics usually describes the common behaviour of visible, ultraviolet, and infrared light.

Optical systems often use transparent materials like glass or plastics with a refractive index selected to bend the light rays to form any type of desired images. And in the case of the human visual system, our eyes have to form images of a large field of view for objects placed at different distances with high resolution at least at a central area of the retina and the most important thing is that these tasks have to be accomplished using living tissues present in the human system. Naturally, the eye as an optical instrument is really very important because our vision is only good when the images formed on the retina are found and formed as high-quality images. If the retinal images are too blurred, the visual system will not work properly and we cannot view the objects clearly.

Optical instruments are the devices that process light waves to enhance the look of an image for a clear view. Besides magnifying distant or tiny images, these devices are used to analyse the properties of optical materials and light. Using an optical instrument (simple magnifying glass, or complicated telescope or microscope) you can make the object look bigger to see fine details on them easily. Remember that for obtaining a bigger image of any object, you have to use converging lenses or mirrors. It is because diverging lenses or mirrors always produce images that are virtual, upright, and smaller than the objects. It means that if you want to understand the concept behind the working of optical instruments, you should know about converging and diverging lenses. So, let's start. 

(Image will be uploaded soon)

When using a converging lens, it is crucial to remember some rules like if the object is far, then the image will be small and close to the focal length. As the object moves towards the lens, the image enlarges and moves beyond the focal length. If the object is placed at 2F, which is twice the focal distance from the lens, both the image and object become the same in size. When the object moves towards the focal point (F) from 2F, the image keeps moving away from the lens and growing until it reaches infinity (∞) when the object reaches F. If the object moves (more) closer to the lens, the image moves towards the lens from negative infinity and becomes smaller. The closer the object gets to the lens, the smaller the image becomes. Note that the converging mirror also works on the same rules.

(Image will be uploaded soon)

Now, if we talk about a diverging lens, it is defined as a lens that causes a beam of parallel rays falling on it to diverge after refraction. Because of being thinner at the centre in comparison to the edges, a diverging lens always produces a virtual image. Unlike any converging lens, the diverging lenses always produce images that are located on the same side of the lens where the objects lie, virtual, upright, and reduced in size, i.e., smaller than the specified object. Besides, as the location of the object does not affect the image, the characteristics of the images formed by diverging lenses are easily predictable.

Thanks to our scientists and inventors with the help of whom, we nowadays, are available with a wide range of optical instruments. Being one of the most useful devices of optical science, instruments like a telescope, microscope, and many others play a vital role in our lives. These are used in performing various tasks and thereby have their applications in several areas. 

Applications of Optical Instruments

Multiple Lenses: As the word multiple suggests, these are devices that include multiple lenses. There are several devices like microscopes and telescopes that use multiple lenses to form images. By analysing any system with multiple lenses, we can conclude that it works in stages where each lens creates an image of the object. As per the working procedure, the original object in such devices acts as the object only for the first lens, and the object for the second lens will be the new image formed by the first lens and so on.

To understand this, you can go through the below examples.

1. Microscope

A microscope is one of the most widely used optical instruments consisting of only one lens or combination of the lenses for magnifying and inspecting bodies which are too small to be seen in detail by naked eyes. Earlier microscopes had only one lens, and therefore, known as simple microscopes, but the present microscopes are available with at least two lenses and thereby, termed as compound microscopes. 

(Image will be uploaded soon)

In general, a microscope consists of two converging lenses. The main reason for including two lenses instead of one is that with two lenses, it is easier to get remarkably higher magnification. For instance, if you want a magnification of 35, you can use the first lens to magnify by a factor of 5 times and the second by a factor of 7 times. Well, doing this is quite simpler than to get a magnification of 35 by using a single lens. The ray diagram of a microscope arrangement (given below) shows that the real image created by the first lens is the object for the second lens. Note that the image, which you see while looking through the microscope is the one created by the second lens. Also, note that the final image formed is virtual and inverted in comparison to the original object. Moreover, the same result is true for several types of microscopes and telescopes.

(Image will be uploaded soon)

2. Telescope

A telescope is another significant optical instrument. It makes distant objects appear nearer by using an arrangement of lenses or lenses and curved mirrors used to observe the objects by emission, absorption, and reflection of their electromagnetic radiation to provide a magnified image. As the telescopes are used to view objects that are far away, they include at least two lenses. These instruments are designed in such a way that the image created by the first lens is smaller and nearer to its focal length. Moreover, the real and inverted image formed by the first lens is closer to the second lens as compared to its focal length. By using the magnifying glass, the device further gives an enlarged virtual image. The final image formed here is inverted in comparison to the object. However, this thing hardly matters in the case of astronomical telescopes, but when it comes to observing the object which is on the earth, most of us possibly prefer to see an upright or straight image. To get an upright or straight image, the third lens is used.

Conclusion

This article is about optical instruments and their properties. It is specifically designed by our subject matter experts for the better understanding of students. Students can refer to this for a more comprehensive approach towards learning and exams.