The key difference between Newtonian and Cassegrain telescope is that Newtonian telescope makes use of a diagonal mirror to reflect the light out of the side of the telescope, whereas Cassegrain telescope uses secondary mirrors to reflect light back through a hole in the primary mirror’s center.
The Newtonian telescope is fundamentally different from the Cassegrain telescope. They are different from each other based on the layout, optical principle, advantages, and disadvantages.
CONTENTS
1. Overview and Key Difference
2. What is Newtonian Telescope
3. What is Cassegrain Telescope
4. Newtonian vs Cassegrain Telescope in Tabular Form
5. Summary – Newtonian vs Cassegrain Telescope
What is Newtonian Telescope?
A newtonian telescope is a device that is able to reflect light and is a telescope that was invented by Isaac Newton in 1668. It is also known as the Newtonian reflector. The components of this system include a concave primary mirror and a flat diagonal secondary mirror. This was the earliest functional telescope and had a simple design, which made it very popular.
The primary mirror is named the “objective.” It is usually in a parabolic shape, and the secondary mirror is a smaller one comparatively. The mirror collects the light that is coming from a pointed region of the sky. Consequently, the second mirror can redirect the light out of the optical axis at a 90-degree angle to make it easy to be viewed with an eyepiece.
The most important advantages of the Newtonian telescope include the absence of any chromatic aberration that can be found in other types of reflecting telescopes, low cost, the presence of only one surface that has to be ground and polished into a complex shape, and the short focal ratio.
However, there are some disadvantages as well. For example, it displays an obstruction at the center because of the secondary mirror that can be found in the path of the light. Collimation is another problem. Similarly, the focal plane of this telescope exists at an asymmetrical point, and it is at the top of the optical tube assembly.
What is Cassegrain Telescope?
Cassegrain telescope is a combination of a primary concave mirror and a secondary convex mirror that is often useful in optical telescopes and radio antennas. The main characteristic of this system is the optical path folding back onto itself. This is relative to the primary mirror entrance aperture of the optical system. The convex secondary adds a telephoto effect and creates a longer focal length in a system that is mechanically short.
When considering the symmetrical Cassegrain, it has both its mirrors aligned about the optical axis and the primary mirror, which usually contains a hole in the center. Therefore, it permits the movement of light toward an eyepiece, an image sensor, or a camera. Moreover, the classical form of the Cassegrain configuration uses a parabolic reflector as the primary mirror, where the secondary mirror is hyperbolic.
What is the Difference Between Newtonian and Cassegrain Telescope?
The key difference between Newtonian and Cassegrain telescope is that Newtonian telescope has a diagonal mirror to reflect the light out of the side of the telescope, whereas Cassegrain telescope has secondary mirrors to reflect light back through a hole in the primary mirror’s center. Moreover, Newtonian telescopes are known for their light-gathering ability, while Cassegrain telescopes are perfect for amateur astronomers looking for quality optics.
The below infographic presents the differences between Newtonian and Cassegrain telescope in tabular form for side by side comparison.
Summary – Newtonian vs Cassegrain Telescope
The key difference between Newtonian and Cassegrain telescope is that Newtonian telescope makes use of a diagonal mirror to reflect the light out of the side of the telescope, whereas Cassegrain telescope uses secondary mirrors to reflect light back through a hole in the primary mirror’s center.
Reference:
1. “Cassegrain Telescopes.” Clifton Cameras.
Image Courtesy:
1. “Newtonian telescope with woman looking through it” By Bin im Garten (CC BY-SA 3.0) via Commons Wikimedia
2. “Cassegrain.en” By Szőcs Tamás Tamasflex – Own work (CC BY-SA 3.0) via Commons Wikimedia