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
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.
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:
#1. Meade Instruments 1010-60-03 LX200-ACF 10-Inch (f/10)
Key Features
- 10” ACF (Advanced Coma-Free) design
- f/10, 2500mm focal length
- Ultra-High Transmission Coatings (UHTC™)
- Built-in GPS
- Built-in AutoStar II software with 145,000+ object database
- Includes standard field-in tripod with dual-fork mount
- Includes Series 4000 26mm Super Plössl Eyepiece
- Includes 8X50 Optical Viewfinder with Crosshair
Pros and Cons
Pros:
- AutoStar II function works very well, automatically pointing when properly aligned to more than 145,000 sky objects in its database
- Sharp and bright images with highly defined contrasts
- Easy to assemble, alignment takes only minutes
- Excellent image resolution
Cons:
- The finder scope is not of the highest quality
- Steep learning curve for the AutoStar II software
- Motors are a little noisy
Our Verdict
The Meade Instruments LX200 Series 10″ ACF is certainly not an affordable Schmidt Cassegrain telescope by any means, but it does pack pretty powerful features. With a focal ratio of f/10, it is more than adequate for planetary and lunar observation and is especially great for deep-space observation.
The LX200 is a Schmidt Cassegrain with a coma-free design, allowing diminished diffraction spikes and less visual aberrations. It is also a fairly heavy telescope, but it can be a good thing since it’s very stable and can withstand heavy winds and other conditions.
Probably not a telescope for first-timers and hobbyists due to its price tag, but it is a great telescope to upgrade to if you are serious about astronomy, especially if you are also interested in astrophotography since the Meade Instrument LX200 can produce very sharp and clear images.
#2. Celestron NexStar 8SE Telescope
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.
#3. Celestron NexStar 6SE Telescope
Key Features
- 6” aperture
- Fully-automated GoTo mount, featuring a database of more than 40,000 celestial objects
- Easy to assemble and break down with a single-fork arm design
- Free Starry Night software
- 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:
- Relatively affordable price for all the features you get
- Fully-automated GoTo mount automatically locates and track space objects
- Celestron SkyAlign technology for easier alignment and assembly
Cons:
- Steep learning curve for those with limited computer knowledge
- Initial physical assembly can be tricky for beginners
Our Verdict
Another one from Celestron, but Celestron NexStar 6SE features a 6” aperture rather than an 8” aperture, so it’s more affordable than the NexStar 8SE discussed above.
Unfortunately, it also has the same relatively bulky weight (30 pounds when fully assembled), so it can be quite difficult to move around with it.
Fair price for all the features you get, and a great, versatile investment for both beginner and intermediate-level astronomers.
Best Maksutov Cassegrain Telescopes
#1. Celestron NexStar 90SLT Computerized Telescope
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.
#2. Orion 9823 Apex Maksutov-Cassegrain Telescope
Key Features
- Compact and portable Maksutov Cassegrain design, offering great views during day and night
- 102mm (4 inches) aperture
- 1300mm focal length, more than adequate for lunar observation, planetary observation, and viewing deep-sky objects as well as terrestrial observations
- Includes 25mm Sirius Plossl, 1.25″ eyepiece, 6×26 correct-image finder scope, 45-degree correct-image diagonal, soft carry case, and Starry Night software
Pros and Cons
Pros:
- Pretty affordable while offering a pretty decent set of features
- Very little chromatic aberration considering its price tag
- 1300 mm of focal length in a compact telescope tube that is also lightweight. The long focal length allows the use of eyepieces with longer focal
Cons:
- Pretty long cool downtime, but most of the time this is not a problem. Simply put this telescope outside for an hour or so before observation
- Doesn’t include a tripod/stand
Our Verdict
As a Maksutov Cassegrain telescope, the Orion 9823 Apex offers a really good contrast with very little chromatic aberration. However, as with any Maksutov telescopes, it is pretty heavy although it is pretty compact so transportation shouldn’t be much of an issue.
The 25mm lens is more than adequate for lunar viewing, but you might need additional eyepieces to view, for example, Jupiter.
#3. Meade Instruments ETX90 Maksutov-Cassegrain
Key Features
- 90mm aperture Maksutov Cassegrain
- 12500 mm (f/13.8) focal length, ideal for high-resolution visual observation
- Capable for astrophotography
- Computerized go-to technology features Meade AuidioStar 30,000+ object database
- Portable and versatile single-arm mount with built-in handle
- Includes (1) Super Plössl 26mm Eyepiece (1) Red-dot Viewfinder (1) 1 25″ Diagonal Mirror (1) Bubble Level/Compass & (1) Meade AutoStar Suite Astronomy Planetarium Software DVD
Pros and Cons
Pros:
- Longfocal length of 1250 mm for its price
- Ultra-sharp image quality
- Great GoTo auto-alignment mount with 30,000+ object database
- High-quality and durable build with great servo motors
- Easy to use and assembly
Cons:
- Relatively small aperture (common in Maksutov telescopes)
- Not very portable
Our Verdict
The Meade ETX90 is a really good beginner telescope, especially for those who are primarily interested in viewing the Moon and planets in our Solar system. Can produce very sharp and high-contrast images, but as a Maksutov, has a relatively small aperture of only 3.5”.
Simple to assemble and use, and it uses AudioStar, a database containing over 30,000 objects so you can easily align the telescope to your object of interest.
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: