How does an optical telescope work

10 facts you need to know about telescopes

The enlargement of a telescope results from the telescope focal length f divided by the focal length feyepiece of the eyepiece: V = f / feyepiece. For example, an eyepiece with a focal length of 20 millimeters on a lens telescope with an objective focal length of 1200 millimeters provides 60-fold magnification. Theoretically, enormous, hundreds of times magnifications can be generated with optical tricks. Above a sensibly usable magnification, however, optics no longer provide any further details of the object: the image may even appear blurred, depending on the air turbulence. A practical rule of thumb is that the maximum magnification that can be sensibly used corresponds to twice the opening specified in millimeters. With a telescope with an opening of 100 millimeters, you should therefore not magnify more than 200 times.

6. What does "apparent field of view" mean?

The eyepieces offered are just as diverse as the types of telescopes available on the market. Here, too, there are important parameters for the selection. Depending on their optical construction, different eyepieces on the telescope result in different viewing behavior. This is especially important for a high level of viewing pleasure apparent field of view decisive. It is given in degrees and describes the viewing angle that the eye can see when looking through the eyepiece. It is a fixed property of an eyepiece and therefore does not depend on which telescope you are using the eyepiece on. The following images illustrate the apparent field of view using the moon.

7. What is the Spaceview Effect?

The apparent fields of view differ depending on the construction principle of an eyepiece. While the simple classic Huygens eyepiece is only 30 degrees, the modern eyepieces reach 100 degrees. From an opening angle of 60 degrees one speaks of wide-angle eyepieces, from 82 degrees of ultra-wide-angle eyepieces. Even Plössl eyepieces with their apparent field of view of 50 degrees give the impression of looking into a tunnel; Wide-angle eyepieces and even more ultra-wide-angle eyepieces come very close to the natural field of view of the eye, which is why observations with them give the impression of being in the middle of the action, one speaks of the "spaceview effect".

8. How much of the sky can I see?