Best telescopes for viewing planets

Maksutov Cassegrain vs Schmidt Cassegrain Telescope

Cassegrain telescopes are typically characterized by having a combination of a primary concave mirror and a secondary convex mirror, which was invented by the French priest Laurent Cassegrain.

When it comes to Cassegrain telescopes, they are quite popular among hobbyists and amateur might have owned at least one Cassegrain telescope at some point in their astronomy ‘career’.

However, Cassegrain telescopes can be divided into two different types: Maksutov (MAK) and Shmidt (SCT), each with its own characteristics and benefits.

In this guide, we will learn all you need to know about the differences between these two types of Cassegrain telescopes, so you can make a better decision in choosing the right one according to your needs.

Why are both designs called “Cassegrain”?

Before we delve further into the differences between the two models, let us first discuss the concept of Cassegrain design itself so we are on the same page.

Cassegrain telescopes have two main characteristics, both are also there in Maksutov and Schmidt telescopes:

The compound optics configuration 

Cassegrain telescopes use a variation of optics that is known as ‘compound’ or ‘hybrid’ optics, which combines both reflector and refractor techniques that are used in refractor and reflector (Newtonian) telescopes.

Typically the optics configuration in a Cassegrain telescope is a concave primary mirror that goes across the bottom plane of the telescope’s tube, while a convex secondary mirror reflects light through the hole in between the primary mirror.

An important consideration is that the primary mirror in most Cassegrain telescopes is spherical in shape rather than parabolic, so the images you’ll see will typically have spherical aberration, and typically a corrector lens is placed to tackle this issue.

Stationary eyepiece

Unlike reflector and refractor telescopes where you can move the eyepiece going in and out while focusing the image in the viewfinder, Cassegrain telescopes mostly feature a stationary eyepiece compartment. So, to focus a Cassegrain telescope, we’ll need to move the whole primary mirror up and down the tube.

In the past, this used to be a massive problem since the mirror components needed to be realigned every time we attempted to focus the Cassegrain. However, mirror locks have since been implemented to prevent this issue.

We now know that both Maksutov and Schmidt-Cassegrain telescopes work with the above principles. So, what are the differences between the two?

Let us first discuss how a Schmidt Cassegrain works.

How Do Schmidt Cassegrain Telescopes Work?

The Schmidt Cassegrain telescopes, also called “Schmidt telescopes” or just “SCTs” are actually one of the most popular types of telescopes due to their compact design, relative affordability, and versatility.

Schmidt telescopes are mainly known for their compactness, only being around twice as long as their aperture. Newer Schmidt telescopes are computerized, further aiding their ease of use and portability.

So, a Schmidt Cassegrain telescope can offer a very short tube while also offering a long focal length.

The main principles of how a Schmidt Cassegrain works are similar to that of a standard Cassegrain telescope: a primary mirror with a central hole reflects the incoming light back and focuses it.

The reflected light will then strike the secondary mirror, which will reflect it through the primary mirror’s central hole into the focuser at the very back of the telescope’s tube.

What’s unique about the Schmidt Cassegrain telescopes is the Schmidt plate, an aspheric lens which is mounted at the front of the telescope to correct spherical aberration (which as discussed above, is common in older Cassegrain telescopes). The Schmidt plate also protects the telescope interior from dust and debris.

SCTs, however, do have their disadvantages, mainly their small aperture ratio of only 1:10 or less, so they are not suitable for astrophotography. Schmidt Cassegrain telescopes are also prone to showing field curvature.  Also, with the long focal length, they produce a relatively small field of view.

How Do Maksutov Cassegrain Telescopes Work?

In its basic principles, Maksutov Cassegrain telescopes work just the same as a Schmidt Cassegrain telescope discussed above with a spherical primary mirror and a secondary convex mirror.

So, the basic design is similar, and in regards to how a Maksutov Cassegrain works, it is also similar to a Schmidt Cassegrain, or any Cassegrain telescopes for that matter.

However, the Maksutov Cassegrain is unique in using a meniscus-shaped lens at the front aperture rather than a Schmidt plate (as you’ll find in a Schmidt Cassegrain). This lens was invented by the Russian engineer Dmitry Dmitriyevich Maksutov, hence the name.

With the constant thickness of this meniscus lens, the telescope only has a little amount of chromatic aberration and it can also correct the spherical aberration produced by the primary mirror. To accommodate this design, the secondary mirror of the Maksutov is vapor-deposited and metal-coated onto the back of this meniscus lens.

With this design, a Maksutov Cassegrain can provide very good contrast, very close to that of a refractor telescope.

However, it does have some downsides like its long cool-down time, and they are typically heavy due to the meniscus lens. Similar to Schmidt Cassegrain telescopes, Maksutov telescopes also have a relatively small field of view with a small aperture ratio (between 1:10 and 1:13).

Maksutov Cassegrain vs Schmidt Cassegrain – Key Differences

As we can see, the main difference between the two Cassegrain ‘subtypes’ is the corrector lens at the front of the scope. A traditional (or classical) Cassegrain telescope doesn’t feature any corrector lens, but will instead use aspherical mirrors to eliminate aberrations.

It’s worth noting that aspherical mirrors are expensive and difficult to manufacture.

Schmidt Cassegrain telescopes use a Shmidt plate (Schmidt corrector lens) while a Maksutov Cassegrain uses a meniscus-shaped lens called Maksutov corrector lens.

Let us discuss more of these corrector lenses below.

Schmidt Plate

Maksutov Cassegrain vs Schmidt Cassegrain - Schmidt Plate

Above is the typical light path in a Schmidt Cassegrain. The Schmidt plate is technically an aspheric lens which corrects the spherical aberration of the primary mirror by producing an exact opposite spherical aberration to the main mirror.

The plate is thin and much simpler to manufacture than an aspherical mirror, and it also offers a shorter cool-down time so the Schmidt Cassegrain has a shorter time required to thermally equalize to its outside temperature.

With these qualities, it’s much easier to produce a Schmidt Cassegrain with a big aperture.

Maksutov Corrector Lens

The Maksutov corrector lens (or corrector plate) is a meniscus-shaped corrector lens that is highly curved, as we can see in the image below.

Maksutov Cassegrain vs Schmidt Cassegrain - Maksutov Corrector Lens

The Maksutov corrector lens is much thicker than the Schmidt plate, and this is why Maksutov telescopes are typically made with a smaller aperture since manufacturing this thick Maksutov corrector lens with a big aperture is difficult and expensive.

Another disadvantage of the Maksutov design is that most commercially-available Maksutov telescopes only feature a small aluminized spot on the corrector lens instead of the secondary mirror. However, typically this won’t be an issue in small apertures.

On the other hand, since the secondary mirror is smaller than in a Schmidt Cassegrain, there’s less obstruction in the light path, resulting in a sharper image with a brighter contrast.

Maksutov Cassegrain vs Schmidt Cassegrain – Which is Better?

To summarize what we’ve discussed above, the Maksutov Cassegrain produces much better images than the Schmidt telescopes, but at smaller apertures.

So, there is no one-size-fits-all answer to the question: which of the two is the better telescope. Rather, it depends ultimately on what object you are looking to observe.

Both telescopes have their unique advantages and disadvantages, as we have discussed above.

Schmidt Cassegrain telescopes offer excellent optics with a wider field of vision, so they are generally better for lunar observation, planetary observations (especially Jupiter and Mars), viewing binary stars, and astrophotography. They are also great for terrestrial viewing.

It is also worth noting that Schmidt Cassegrains are very compact and easy to use, while only requiring little maintenance. However, they are more expensive when compared to Newtonian reflector telescopes with comparable aperture.

Also, there are astronomers who simply don’t like the look of a Schmidt Cassegrain telescope due to its very short tube.

As discussed above, the secondary mirror design in a Schmidt Cassegrain prevents light from passing through, so contrast-wise, a Maksutov is better.

Maksutov Cassegrain telescopes, on the other hand, are typically available only in smaller sizes (since manufacturing a Maksutov with a bigger aperture is expensive), so they tend to be more suitable for planetary observation and are not fit for deep-sky observation.

They, however, can produce a much clearer image with better contrast, but they aren’t as versatile as a Schmidt Cassegrain.

Price-wise, they are both in the same price range for comparable aperture sizes, but Schmidt Cassegrain is more versatile. If you are looking for a compact telescope with excellent image quality for planetary observation and visual use, Maksutov Cassegrains are better.

To help you make a better decision in choosing between the two, you can check their pros and cons below.

Maksutov Cassegrains – Pros and Cons 

Pros: 

  • Lower manufacturing cost, so they tend to be affordable compared to Newtonian telescopes
  • Very compact, but has a long focal ratio
  • Doesn’t need regular collimation, as the optics are already perfectly aligned
  • They use a secondary spot of reflective coating rather than a proper secondary mirror, which are cheaper to manufacture
  • Great for high-resolution planetary observation, lunar observation, and astrophotography

Cons: 

  • The Maksutov corrector lens/plate is larger and heavier, so it requires more time to thermally equalize itself to the outside temperature
  • Smaller aperture
  • Most field flatteners and/or focal reducers aren’t compatible with Maksutov telescopes, so it can be difficult to correct any aberrations
  • The corrector lens/plate is prone to dew

Schmidt Cassegrain – Pros and Cons 

Pros: 

  • More versatile than a Maksutov, featuring an all-purpose and well-rounded telescope design. Combines the advantages of both reflector and refractor telescopes
  • Easier and cheaper to build a Schmidt Cassegrain with a big aperture
  • Ideal for both deep-sky observations and astrophotography, while also being very good for lunar and planetary observations
  • Long focal lengths, so they can produce high-resolution images
  • Durable and typically maintenance-free, doesn’t require regular collimation

Cons: 

  • Secondary mirror obstructs light, so will reduce contrast performance
  • The field curvature in the optics is not very noticeable
  • The mirror flop can be an issue when changing the direction of the telescope

Best Schmidt Cassegrain Telescopes

Below are our recommendations for the best Schmidt Cassegrain telescopes available in the market today:

Celestron NexStar 8SE TelescopeCelestron NexStar 8 SE Schmidt-Cassegrain Computerized Telescope WiFi Kit - with Skyportal WiFi Module

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Key Features

  • Fully automated GoTo mount with a database of more than 40,000 space objects
  • Compact and portable, easy to transport and assemble anywhere
  • Includes a red dot StarPointer finderscope, 25mm Plossl eyepiece, visual back, and mirror star diagonal
  • 8-inch aperture Schmidt Cassegrain optics
  • Compatible with various Celestron accessories
  • Celestron SkyAlign feature allows easy assembly and alignment so you are ready to observe in minutes

Pros and Cons

Pros: 

  • Easy to mount and use, only need a matter of minutes after opening the box
  • Includes a pretty decent metal tripod, making the telescope pretty stable
  • Great optics, can produce excellent image quality
  • Great GoTo software from Celestron
  • Comes with a pretty good eyepiece

Cons: 

  • Needs a lot of power, so you’ll need an additional power source when using it outdoors
  • You might find it difficult to align this telescope in areas with a lot of light pollution

Our Verdict

Celestron obviously needs no introduction as one of the top telescope makers available today, and the NexStar 8SE is a compact Schmidt Cassegrain telescope that can provide high-definition, clear and sharp images.

It is easy to assembly thanks to its unique design where the optical tube is mounted onto the base via just one, single fork arm.

It is a pretty affordable Schmidt Cassegrain telescope, making it a great choice for hobbyists and amateur astronomer. Compact, yet offers pretty powerful features whether you are a novice or an experienced hobbyist.

Best Maksutov-Cassegrain Telescopes

Celestron NexStar 90SLT Computerized Telescope

Celestron - NexStar 90SLT Computerized Telescope - Compact and Portable - Maksutov-Cassegrain Optical Design - SkyAlign Technology - Computerized Hand Control - 90mm Aperture

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Key Features

  • Computerized telescope with a database of 40,000+ space objects
  • Compact and portable in size, the smallest in Celestron’s SLT family
  • 90 mm aperture, can gather enough light to observe the Moon in its detail, Jupiter’s cloud bands, Saturn’s rings, and more
  • Celestron’s Skyalign feature for easier setup
  • Free Starry Night Software
  • Includes a red dot StarPointer finderscope and 2 eyepieces (25mm and 9mm)
  • Includes a full-height steel tripod

Pros and Cons

Pros: 

  • Great value for money with its price and very good set of features
  • 90 mm (3.5 inches) aperture with 1250 mm focal length ensuring great image quality
  • Easy to use GoTo computerized mount
  • Very easy assembly with the SkyAlign
  • 2 eyepieces included (25mm and 9mm) for versatility

Cons: 

  • 90mm aperture might be too small for deep spade observations
  • No auto timekeeping feature

Our Verdict

The NexStar 90 SLT is another option from Celestron and is actually one of Celestron’s line of beginner Maksutov telescopes. So, it is designed to be affordable, easy to use and assemble, and can provide great quality images for ‘beginner’ observations like lunar and planetary observations and terrestrial viewings.

It is an excellent choice for anyone just entering the world of hobby astronomy with minimum complication and a great set of features.

Final Words…

We hope you’ve learned the key difference between a Maksutov Cassegrain vs Schmidt Cassegrain in this article. The telescopes listed here are among the best at their price point. If you enjoyed this article, consider checking out some of our others: