Magnification and Light gathering

If you want to buy a telescope, you will find a lot of features of the telescope in the advertisements. Before buying it, you should understand all the features to find the telescope that suits you the best. Here we will discuss the feature- magnification power of a telescope.

Magnification Power is the ability of a telescope to magnify the image of the object you are looking at through the telescope. You will find numbers in the features of it like 18x or 50x and so on which are in fact the value of magnification power.

What do I mean by limits in the magnification?

Telescopes are not very simple optical systems. The more expensive the telescope you use, the more complicated mechanism you will find in it. So it has to manipulate light very carefully to avoid distortion. If you look through a small inexpensive binocular or just a magnifying glass, you will find that the image of the object is very unclear, distorted, and of low quality. Yet as their magnification power is less for example 3x or maybe 5x, the image is still seeable, but what if the magnification power is 100x or 500x? 

This higher magnification will never make the image clearer. You will get an even worse and more distorted view. Why does this happen? Because while they are magnifying the image, they are also magnifying the distortions and imperfections. So while buying a telescope, the magnification power is important, but higher magnification power will not benefit you that much. You have to know the limit of this. In short, you will obviously look for higher magnification power, still within a limit.

Limit of magnification power of a telescope

Limit of magnification power of a telescope actually means how much magnification telescopes can provide without making the image distorted much. There is a rule known as ‘60 rule’ or general rule of thumb which determines the magnification power. For this, you need to know the diameter of the telescope in inches and then multiply it by 60. The result will provide the upper magnification limit of the telescope. So if you have a 8 inch telescope, usually this 8 inch is the diameter of the telescope. So we get, 8×60=480, which is the upper limit of your 8 inch telescope. This means that if you observe a clear, dark and calm night sky, 480 is the rough magnification power limit of your telescope.

The thing that is much more important is the light gathering power of the telescope. And this is done by the primary mirror or lens of the telescope. The bigger the mirror or lens the more light it will gather. And this will enable you to see dim objects much brighter. And to see dimmer objects that can’t be seen with smaller telescopes.

So, The bigger the objective, generally the more you will see. And the brighter it will be!

These next two images give you a good sense for what this means. Both images are with the same exact magnification (power) The image on the left is with a smaller telescope. See how it is much dimmer? It appears smaller too. But this is only because the telescope can’t see the lighter details on the edges of the galaxy.

How to Determine Magnification Power of a Telescope

To determine magnification power of any telescope, you just need to know and apply a formula. The ratio of the focal length of the telescope and the focal length of the eyepiece is in fact the magnification power.

Magnification = (objective focal length) / (eyepiece focal length)

Fig 1: Magnification Power Formula of a telescope

How to get higher magnification in a telescope

  1. If a telescope is built with finer optics, it will be able to give higher magnification without much distortion. The better the optics, the better the magnification power of the telescope.
  2. If the mount of a telescope is sturdy enough, it will avoid shaking while viewing any object. This will allow you to get a higher magnification of the image.
  3. If you want to get a higher magnification power telescope, you have to invest a lot of money. Because the better optical system, strong and sturdy mount all cost a lot to build. This is the reason why the best quality telescopes are really expensive.

So, it should be clear to you by now that you really do not need to be disappointed if your telescope can not magnify things by thousand times. The magnification power is not the most important thing to get a better view from scopes. The most significant thing that really matters is the light-gathering power of the telescope.

Magnification power is important while buying eyepieces

Fig 2: Celestron Omni Series 1-1/4 4MM Eyepiece

You will get so many features in the advertisement if you look for buying an eyepiece. Here also you have to carefully choose one that suits the magnification power of your telescope. Different sizes of the eyepiece offer different magnification power. For example: if you have an 8 inch telescope, that can provide 480x magnification power, you do not really need an eyepiece that gives a magnification of 700 or more. Because the more the magnification power of the piece, the more it will cost. So it will not worth the cost then.