There are different types of telescopes available on the market depending on different features. Here we will discuss the tube assembly and light path of five types of telescopes.
Fig 1: tube assembly and light path of five types of telescopes
The image shows how they are different in assembly and lightpaths and they have different reasons for it. Moreover, all of them have a plenty of pros and cons which we are going to review it.
The Refractor telescope
This is one of the oldest models of telescopes and widely used. These design is seen mostly in the beginner scopes.They have an aperture lens and an eyepiece at the two ends. The aperture lens is sometimes called sandwich lenses.
- It has fantastic revolving power
- The performance is satisfying even in inferior conditions
- Light never reflects in this tube assembly
- The optical alignment is nearly permanent- so you do not need to have headache on maintenance.
- The design and eyepiece is simple.
- It has long focal ratios that means longer focus.
- The cost is higher than the reflector telescopes
- It faces chromatic aberration which causes change of color of the image.
The Newtonian Reflector
The reflector telescopes designed by Newton do not use lens, it uses mirror. A small flat mirror is used herre to direct the light to the eyepiece.
- It has better light collection ability than the refractors as it has large mirrors.
- No chromatic aberration
- The cost is relatively low
- Optical quality is sometimes disappointing and not very good for astrophotography.
- You have to collimate it before use and take of mirror cleaning timely.
- The tube is open, so you have to take care of the dusts and humidity.
- A little bit bulky and heavier.
Cassegrain telescopes are unique as they use a mirror, but with a hole at the center. It can direct the light towards the back. The secondary mirror is a concave mirror, i.e. not flat like newtonian. It enhances the focal length and in turn provides better performance. Cassegrain telescopes are not widely available like the other two mentioned before. Schmidt Cassegrain and Maksutov telescopes are made based on this design and they are also very popular.
Catadioptric Telescopes are designed using mirrors and lenses both. There are two types of Catadioptric scopes.
This design uses a spherical mirror. Most importantly it ha a curved and thin piece of glass at the very front that helps to correct the output of spherical mirror.
- This is great for sky observation and astrophotography.
- The optics can be folded that makes it lighter and shorter.
- It has a focal reducer so that you can use it in versatile purpose.
- It is expensive
- Views are narrower and exposures are longer
- The contrast is less and sometimes need collimation
This design also includes the correcting glass at the front. The secondary mirror is basically an aluminized circle attached with the glass.
- Good for planetary views.
- Optics are folded
- More affordable
- Only one focal length
- High quality and expensive
- Long focal ratio