Introduction
Parabolic and Spherical mirrors are 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 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 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
We’d like to give you a heads-up before we get into a full-fledged debate. It’s always advantageous to be aware of key distinctions. For example, there are 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 difficult to understand. Hence, choosing between them gets that much tougher. After reading this guide, you should be able to decide which one to purchase.
Aperture
The aperture is a very important feature in mirrors. An opening on the lens controls the amount of light entering your telescope. The image will be brighter and sharper as the aperture is increased.
The aperture of a parabolic mirror is 60mm. This means they can 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 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 similarly. If that doesn’t happen, spherical aberration takes place.
There are no aberrations in parabolic mirrors, regardless of where the light rays fall. 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 lenses 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. On the other hand, parabolic mirrors can’t be done by a machine. Indicators are needed 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 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.
Spherical mirrors can be a great choice if you’re tight on budget.
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.
On the flip side, parabolic mirrors don’t have any of these requirements. Regardless of focal length, you can obtain a more focused image.
These are the distinctions you’ll need to remember while making a decision. On a side note, properly cleaning the telescope optics will increase its longevity.
Our Verdict
Both parabolic and spherical mirrors are great choices. Although, the former is slightly ahead.
You won’t regret getting parabolic mirrors for your telescope if you’re not on a budget. 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 plan to switch mirrors, please 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 central 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 a parabola used in mirrors?
Answer: The parabolic shape converges 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.
Could you let me know if you managed to find what you were looking for? Always remember to take extra care of mirrors, so they don’t break. They’re pretty expensive to replace.
Take care and good luck!
