Is the magnification of a telescope bigger the better?

The telescope is a kind of visual optical instrument used for observing distant objects. It can enlarge the small Angle of distant objects by a certain magnification so that it has a large Angle in the image space so that the objects that can not be seen or distinguished by the naked eye become clearly discernible.  Therefore, the telescope is an indispensable tool in astronomy and ground observation.  It is a kind of optical system through the objective lens and eyepiece so that the incident parallel light beam still remains parallel to exit.  

Many people think that the magnification of a telescope should be as large as possible. In fact, the magnification of a telescope is determined by many factors. The practice has proved that the most suitable telescope for hand-held observation should be 6-10 times, and 7 or 8 times is the most.  Telescopes on the market are usually not more than 20 times, if marked hundreds of times, thousands of times, then it is no doubt fake.  

The boat for sightseeing

Is the magnification of a telescope bigger the better?

In fact, there are no technical difficulties with high-power telescopes. You can go as high as you want, but there are a lot of negative consequences.  The first is brightness. The higher the multiple, the worse the surface brightness of the object will be, because the area of the object is magnified proportional to the quadratic magnification, and the brightness decrease will be very obvious.  

Of course, if the telescope aperture is large, the multiple can be appropriately high, but the hand-held telescope aperture is generally not more than 50mm.  Even more important is the jitter caused by high power. Handheld telescopes have slight jitter, but this slight jitter becomes very noticeable when magnified.  

In summary, telescope magnification has the following disadvantages:  

First, the magnification is too large to be stable.  What is the use of enlarging the magnification of the telescope when the wobble of the image makes it impossible for the human eye to fully observe the details of the image?  If the telescope can be fixed on the tripod, then the magnification can be higher, but for the ground observation telescope, due to the aforementioned brightness and resolution constraints, the magnification can not be too high, otherwise, the image will be very dim and fuzzy, at the same time, the field of view is too small, it is difficult to find the target.  

Second, large magnification will reduce the actual field of vision.  The larger the multiple, the smaller the area that can be viewed simultaneously.  It is not conducive to finding and looking for targets, especially for the observation of frequently changing targets.  Even if you find your target, it’s easy to lose it if the shelf wobbles.  

Third, in the case of the same objective aperture, the larger the multiple, the lower the inverse square ratio of brightness.  The decrease of object brightness will directly affect the observation effect of human eyes.  

Fourthly, large magnification is generally achieved through a short focal length eyepiece.  The short focal length of the eyepiece can cause uncomfortable observation and is not suitable for eyewear.  

Fifthly, too large multiple selections exceed the theoretical resolution limit, resulting in invalid amplification.  There is a theoretical limit to the resolution of a telescope.  Because one of the functions of a telescope is to look at the detail, when the magnification is too large, because of this theoretical limit, there is no more detail to zoom in, so it is meaningless.  

The choice of magnification depends not only on the theoretical resolution of the telescope but also on the observing conditions at that time, especially on the observer’s own eyesight.  The selection multiple is the number of millimeters of the aperture of the objective lens multiplied by 1.5, which is a reference value for ordinary conditions.  

Share this post