Most Important Functions of a Telescope

Breaking myths

Most of us think that magnification is the most important function of a telescope. But is that so?

NO!!

Magnification is preceded in the order of importance by two very important functions- Light grasp and resolution. Let’s look at them one by one in detail.

Light Grasp

Suppose you are watching the night sky with your naked eye, What do you see? Maybe a few dimly shining dots from the streets of your city. But from a telescope, you can see many more of the stars in the same region of the sky where you were not able to spot any distinct thing. With an even bigger telescope, this view becomes more elaborate. Isn’t it? This is simply because of the difference in the light grasping power of our eyes and the telescope.

In layman’s terms, light grasp simply means how much light can a telescope collect. This means a telescope with a more light grasp would be able to show stars that are a long distance away, while a telescope with lower light grasping power may not perform this function.

The light grasp of a telescope depends on the telescope’s objective lens/mirror diameter. This is the part of the telescope from which light first enters the system to show us the images of celestial bodies. It can be understood that a large area will take in more light.

This function of the telescope is not only performed by the telescope but also by the observer. The image perceived by the observer varies with the observer’s eye’s pupillary aperture. This feature of the eye of decreasing its pupillary aperture rusts with old age. Hence younger people can see far away objects from telescopes more clearly.

Resolution

Let’s try to understand this second feature with an example. Suppose you are looking at the night sky trying to find Alpha Centauri-a binary pair of stars. From the naked eye or even a small telescope, they would appear to you as one star. But as we observe from bigger telescopes with more resolution, we would be able to see both the stars of the system distinctly.

The resolution of an instrument is the separation of the closest double star it will show distinctly.

Magnification

Magnification is simply defined as the focal length of the objective divided by the focal length of the eyepiece.

In simple words with more magnification, we see a bigger image of the object since we are viewing a small part of the sky.

But a shocking thing for an amateur is about approach…. Did you know that increasing the magnification would reduce the brightness of the object you are observing?

Note-

These features of the telescope are not only influenced by the instruments but also by the atmosphere around them. For e.g. if the atmosphere is dusty it would give less resolution. Similarly, in the summer season, higher magnification would produce blurry images since the warm air from the ground would be rising upwards but the opposite would happen in winters. Therefore we would be able to distinguish between objects in the night sky more clearly.

Conclusion

Thus now that we have understood the importance of each of these functions of the telescope, we can make an informed choice on which telescope to buy, rent or build;)