parabolic vs spherical mirror

Parabolic Vs Spherical Mirror: The Best Choice

Introduction

Parabolic and Spherical mirrors are two of the most common ones used in telescopes. Both have their pros and cons. This is why many users are left perplexed while making a decision. We hope to make your life a bit easier with this guide.

So, which one would be the ideal choice: parabolic vs spherical mirror?

To begin with, spherical mirrors are less expensive to manufacture. They’re also easier to make. But, unlike parabolic mirrors, they have spherical aberration. When it comes to the aperture, parabolic mirrors lead. They also require a lower focal ratio. And, as for coma, Parabolic mirrors suffer from it.

This was only a brief glance at the comparison. You’ll need more knowledge to make a decision. So why not spare a few minutes?

Let’s begin!

Parabolic Vs Spherical Mirror: Short Overview

Let us give you short heads up before we get into a full-fledged debate. It’s always advantageous to be aware of key distinctions. For example, there’s a lot of differences when it comes to PVS-7 and PVS-14. Moreover, it’ll improve your understanding of the comparison and provide more clarity.

Time is a luxury nowadays. This is why we’ve prepared a brief table so you can get a general idea- 

Features Parabolic Mirror Spherical Mirror
Diameter 20’’ 24’’
Focal Length  10m 12m
Surface Area  Lower Greater
Price Less expensive More expensive
Surface Quality 10-5 scratch/dig 60-40 scratch/dig
Aperture 40mm 60mm

You should now have a working knowledge of these mirrors. As a result, we can now go ahead with the in-depth discussion.

Parabolic Vs Spherical Mirror: In-Depth Comparison

Parabolic and spherical mirrors are a bit difficult to understand. Hence, choosing between them gets that much tougher. You should be able to decide which one to purchase after reading this guide.

Aperture

Aperture is a very important feature in mirrors. The amount of light entering your telescope is controlled by an opening on the lens. The image will be brighter and sharper as the aperture is increased.

The aperture of a parabolic mirror is 60mm. This means they have the ability to absorb a large amount of light. As a result, they can create sharper, more detailed images.

The 40mm aperture of spherical mirrors isn’t that bad. But, it won’t give you the same satisfaction as with parabolic mirrors. This is similar to that of Lunt and Coronado.

Spherical Aberration

A lens’s outer and inner surfaces must both focus light rays in the same way. If that doesn’t happen, spherical aberration takes place.

In parabolic mirrors, regardless of where the light rays fall, there are no aberrations. Rays that are reflected will always pass through the same focal point. This is not true of spherical mirrors.The focus of marginal and paraxial rays differs due to aberration.

As for image quality, using parabolic mirrors is better as aberration causes blurry images.

To make your job easier, we’ve compiled a list of some high-quality lenses. Here are the top two best lens that we recommend-

Product 1 Product 2

Hopefully, you won’t be disappointed with your recommendation. Let’s carry on,

Manufacturing

In this segment, we’ll find out which mirror is cheaper to produce. 

A spherical mirror is inexpensive and can be created by machine. This is because the parts they require are cheaper. Parabolic mirrors, on the other hand, can’t be done by a machine. Hands are required to create them.

These mirrors have to be designed so that the edges are flatter.  This’ll allow the light to be focused at a single point. Machines cannot do that. Due to the difficulty of making parabolic mirrors, their manufacturing costs shoot up. 

You’ll be able to see the same difference in manufacturing costs between Cassegrain and Newtonian.

Price

Price is a factor almost everyone takes into account during purchase. Especially if they’re on a budget. 

Since it’s more expensive to produce parabolic mirrors, their price is higher than spherical mirrors. 

Parabolic mirrors can be purchased for around $70-80 depending on where you go. As far as spherical mirrors are concerned, you’ll get them for $40-60. 

If you’re tight on budget, spherical mirrors can be a great choice. 

Focal Length

One of the most important aspects of mirrors is their focal length. The magnification power of a mirror increases with its focal length.

To get a clearer image, the focal length of the spherical mirror must be small. It must be in the f/10 range. Or, the circumference of the telescope has to be larger. 

Parabolic mirrors, on the flip side, don’t have any of these requirements. Regardless of focal length, you will be able to obtain a more focused image.

These are the distinctions you’ll need to keep in mind while making a decision. On a side note, cleaning the telescope optics the proper way will increase its longevity. 

Our Verdict

At the end of the day, both parabolic and spherical mirrors are great choices. Although, the former is slightly ahead.

If you’re not on a budget, you won’t regret getting parabolic mirrors for your telescope. They’ll give you a whole new experience. On the other hand, if you have a high-end telescope,  a spherical mirror will be enough.

FAQs

Question: Which telescopes come with parabolic and spherical mirrors?

Answer: Reflector telescopes like Schmidt-Cassegrain, Newtonian, and Cassegrain come with parabolic mirrors. In reverse, Celestron, Sky-Watcher, and Orion are equipped with spherical mirrors. If you’re planning to switch mirrors, remember to check if your telescope supports it.

Question: What causes coma in parabolic mirrors?

Answer: The curvature of the optical system’s principal planes causes a coma. It can occur even at short distances from the principal axis. Furthermore, differences in refraction cause the comet-like shape in comatic aberration. This is because light rays pass through the various zones of the lens.

Question: Why is parabola used in mirrors?

Answer: The parabolic shape is used to converge parallel rays in a single point. It doesn’t matter where rays strike the mirror’s surface. Consequently, the parabolic mirror is an important part of a reflecting telescope.

Conclusion

We’ve now reached the end of our guide on parabolic vs spherical mirrors.

Did you manage to find what you were looking for? Always remember to take extra care of mirrors so that they don’t break. They’re pretty expensive to replace.

Take care and good luck!

Scroll to Top