Different types of scopes
There are multiple types of scopes for Astronomy. All have varying uses, advantages, and disadvantages. Below is the listing of most of the types of scopes available. 99% of all telescopes can be used for Visual use and this page is designed for beginners coming into astronomy and looking at the visual side of this hobby.
There are multiple types of scopes for Astronomy. All have varying uses, advantages, and disadvantages. Below is the listing of most of the types of scopes available. 99% of all telescopes can be used for Visual use and this page is designed for beginners coming into astronomy and looking at the visual side of this hobby.
Newtonian Reflector
The Newtonian reflector, known as a Newtonian telescope or just Newtonian, is a reflection-type telescope with primary and secondary mirrors. Sir Isaac Newton designed Newtonian reflector telescopes. This style of telescope uses a concave style primary mirror and a flat secondary mirror which reflects the light to an eyepiece near the top of the telescope. These styles of scopes have several advantages and disadvantages. |
Advantages
Reflecting scopes only need a perfect surface which reflects light, unlike refractor scopes and similar style scopes which need to be perfect and free from imperfection throughout the lens.
Reflecting mirrors can be supported around the edge and at the back of the mirror, avoiding sagging due to gravity.
- Free of chromatic aberration
- Newtonian telescopes are generally cheaper
- Ranges from 75mm – 300mm in aperture (can be larger but designed for professional use in labs and Observatories)
- Shorter focal ratio leading to wider FoV
- Easier for visual users due to the location of the focus wheel and eyepiece.
- Central obstruction due to the secondary mirror location
- Secondary mirror attachment causes diffraction spikes on the stars, which are more prominent on the larger stars
- These sorts of scopes suffer from coma aberration which will require additional accessories to correct it
- Newtonian scopes require collimation regularly
Reflecting scopes only need a perfect surface which reflects light, unlike refractor scopes and similar style scopes which need to be perfect and free from imperfection throughout the lens.
Reflecting mirrors can be supported around the edge and at the back of the mirror, avoiding sagging due to gravity.
Refractors and Apochromatic Refractors
The Refracting telescope is a type of scope which was designed in the 19th century for research purposes, but the popularity of the scopes shifted to reflecting due to the increased aperture. The design of the scopes typically has a lens at the front, a long tube and then the eyepiece. The scope is limited by the aperture and the length for amateur users due to size and weight, which increases the cost as the size of the scope increases. Early on the lenses were one-element glass but as time went on two and three-element lenses were made. A refracting telescope's objective bends or refracts light. Parallel light rays condense at a focal point because of this refraction, whereas nonparallel light rays concentrate at a focal plane. The telescope’s optical axis transforms a bundle of parallel rays into an angle α, resulting in a second parallel bundle with an angle β. The angular magnification is denoted by the ratio β/α. The ratio of retinal image sizes acquired with and without the telescope is identical. To correct image orientation and other types of aberration, reflecting telescopes can be set up in a wide variety of ways. These telescopes are known as refracting telescopes or refractors because the image was created by bending light or refraction. Several advantages and disadvantages go with this type of scope. |
Advantages
The objectives of apochromatic refractors are constructed from unique, extremely low dispersion materials. They are made to focus three wavelengths in the same plane, usually red, green, and blue. When compared to an achromatic lens, the residual colour error (tertiary spectrum) can be up to an order of magnitude smaller. These telescopes create extremely sharp images that are nearly free of chromatic aberration because the objective contains fluorite or unique, extra-low dispersion (ED) glass. Apochromatic refractors are typically more expensive than telescopes of other types with a comparable aperture because of the unique materials required in manufacturing.
- No need to collimate the scope
- The eyepiece is at the back of the scope
- No obstructions at the front lens holding the lens in place
- No diffraction spikes
- No coma correctors are required
- Larger scopes will be long and heavy, especially when considering triplet scopes etc.
- Maximum aperture is around 150mm
- The picture will be curved, so a field flattener will be required (Not all the time, generally on the large scopes and larger sensors. But I found the stars were curved with the smaller 72ed and small sensor)
- Expensive, especially when you start looking at the triplet APO style scopes
- Larger the scope higher the F-number (for AP purposes longer exposures are needed for pictures when compared to shorter F-number scopes)
The objectives of apochromatic refractors are constructed from unique, extremely low dispersion materials. They are made to focus three wavelengths in the same plane, usually red, green, and blue. When compared to an achromatic lens, the residual colour error (tertiary spectrum) can be up to an order of magnitude smaller. These telescopes create extremely sharp images that are nearly free of chromatic aberration because the objective contains fluorite or unique, extra-low dispersion (ED) glass. Apochromatic refractors are typically more expensive than telescopes of other types with a comparable aperture because of the unique materials required in manufacturing.
Dobsonian
A Dobsonian telescope is a Newtonian telescope with an altazimuth mount that was made popular by John Dobson in 1965. It is credited with greatly expanding the size of telescopes that are accessible to amateur astronomers. Dobson's telescopes had a straightforward mechanical design that made it simple to make using widely accessible parts to produce a sizable, transportable, and affordable telescope. The layout is ideal for studying dim deep-sky objects like galaxies and nebulae. This kind of observation needs a portable setup with a big objective diameter (i.e., light-gathering power), a short focal length, and the ability to move to areas with less light pollution. Dobsonian’s lack capabilities seen in other amateur telescopes, such as equatorial tracking because they are meant to be what is known as a "light bucket" working at low magnification. Dobsonian telescopes are well-liked in the world of amateur telescope builders, where the design was pioneered and is still being improved. Additionally, several commercial telescope manufacturers offer telescopes with this configuration. Regardless of the materials used in construction, the name "Dobsonian" is currently used to describe a variety of large-aperture Newtonian reflectors that employ some of the fundamental Dobsonian design principles. |
Positives
As an example – an 8” (200mm) Dobsonian scope from Skywatcher is roughly £375, and a reflector style scope (since an 8” in a refractor will not even be in the same ballpark) costs £338 without the mount (due to the size and weight of the 8” reflector scope (~8kg) a certain type of mount is needed). The price point for starters cannot be beaten with Dobsonian scopes (ignoring the second-hand market as deals can be made here, but it comes with its own risks)
- Cheapest telescope for the size for visual use
- Starter-friendly (recommended for newcomers to Astronomy)
- Comes with a “mount”
- Comes with goto tracking options with certain brands
- Aperture ranges up to 20”
- As mentioned above the mounts do not track equatorial, so AP is harder (not impossible) to do
- The larger Dobsonian are heavy and hard to move about (but not impossible, but people with health issues could potentially struggle)
- No adjustments on the mount for uneven ground (it does not matter as much, but you cannot adjust for the ‘wobble’ due to the hole under one foot of the mount)
As an example – an 8” (200mm) Dobsonian scope from Skywatcher is roughly £375, and a reflector style scope (since an 8” in a refractor will not even be in the same ballpark) costs £338 without the mount (due to the size and weight of the 8” reflector scope (~8kg) a certain type of mount is needed). The price point for starters cannot be beaten with Dobsonian scopes (ignoring the second-hand market as deals can be made here, but it comes with its own risks)
Maksutov
The Maksutov which is commonly known as a "Mak" is a catadioptric telescope design that makes use of the "spherically symmetrical" nature of all the surfaces by fusing a spherical mirror with a weakly negative meniscus lens. The negative lens is typically fully dilated and positioned at the telescope's entrance pupil (commonly called a "corrector plate" or "meniscus corrector shell"). Both chromatic aberration and off-axis aberration issues, such as coma encountered in reflecting telescopes, are resolved by the design. Dmitri Dmitrievich Maksutov, a Russian optometrist, filed a patent for it in 1941. Maksutov based his concept on the Schmidt camera's principle of exploiting a negative lens' spherical mistakes to rectify the opposing ones in a spherical primary mirror. The design can use all-spherical elements, which simplifies manufacture, and is most frequently seen in a Cassegrain form with an integrated secondary. Since the 1950s, Maksutov telescopes have been offered for sale to amateur astronomers. |
The main design of the “Mak” is the reflection of the light from an object to multiple mirrors which leads to the viewpoint. The light first passes through the corrector plate and hits the primary mirror which is situated at the rear of the scope, which reflects to the secondary mirrors situated behind the corrector plate and finally to the viewpoint. Because of all the reflections, the F ratio is generally very high.
A 90mm Mak style scope will generally have a Focal length of 1250mm at F/13.88 with larger apertures focal length exceeding 2500-4100mm depending on the brand and size scope you choose. The F ratio will vary between brands and how they are built, Skywatcher 180mm F ratio is F/15 while for the Meade version at 200mm, the F ratio is F/10 with the price point being the major factor (Meade - £4500 and SW varying between £1500-2500 depending on which mount you choose)
Positives
Not saying these are bad scopes, as for visual these are some of the best, although expensive, for AP, there are better options.
A 90mm Mak style scope will generally have a Focal length of 1250mm at F/13.88 with larger apertures focal length exceeding 2500-4100mm depending on the brand and size scope you choose. The F ratio will vary between brands and how they are built, Skywatcher 180mm F ratio is F/15 while for the Meade version at 200mm, the F ratio is F/10 with the price point being the major factor (Meade - £4500 and SW varying between £1500-2500 depending on which mount you choose)
Positives
- Compact style scopes (until you get to the larger versions of this scope)
- Comes with corrector plates
- Close Field of view for planets or smaller objects
- Price point starting at under £200 for the scope
- Compact size helps balance on mounts
- Price point increases dramatically for the lower F ratio
- The weight of these styles of scopes
- Requires a heavy-duty mount due to the weight
- Can be used for AP but for the price there are better options (a lower F ratio is needed)
Not saying these are bad scopes, as for visual these are some of the best, although expensive, for AP, there are better options.
Maksutov-Newtonian
While this style of scope can fall under either Maksutov or Reflector style scopes as it contains both styles in one design. I felt this would deserve its section due to its design. With one-fourth, the coma of a comparable conventional Newtonian and one-half the coma of a Schmidt-Newtonian, Maksimov’s optics can be employed in Newtonian configurations with little aberration over a broad field of vision. Using a high focal ratio with a diagonal mirror positioned on the corrector that is proportionately tiny can also reduce diffraction, resulting in contrast and image quality that is like that of unimpeded high-end refractors. The mass of the corrector plate restricts the total diameter of the optical system, like the Maksutov-Cassegrain. Currently, Synta Taiwan manufactures a 190 mm model under the Sky-Watcher brand, while Explore Scientific manufactures a 152 mm model created in cooperation with astronomer David Levy. |
Positives
Negative
- Excellent for AP as well as visual observation
- No additional coma corrector is required
- No diffraction spikes due to the corrector plate holding the secondary mirror in place
- Hold calibration extremely well
Negative
- High price point
- Aperture limitations due to the weight of the corrector plate
- Overall weight of the scope is higher than the same size Newtonian scope
Rowe-Ackermann Schmidt Astrograph (RASA)
This style of scope was designed for AP only. It has no means of holding eyepieces and the camera is mounted to the corrector plate at the front which also gives the scope its incredibly fast F ratio of F/2. Currently, these are only available in 8”, 11” and 14” with increasing cost per size jump.
This camera style was designed for dedicated Astro cameras. Depending on the RASA size, it will use cameras under a certain diameter before it obstructs the corrector plate. The RASA is currently only built by Celestron.
The speed of these Astrograph scopes compared to other scopes is extreme and these scopes were not designed for beginners! There is a review and comparison between the RASA 8 and SW 72 ED Pro in the review section (along with pros and cons).
This style of scope was designed for AP only. It has no means of holding eyepieces and the camera is mounted to the corrector plate at the front which also gives the scope its incredibly fast F ratio of F/2. Currently, these are only available in 8”, 11” and 14” with increasing cost per size jump.
This camera style was designed for dedicated Astro cameras. Depending on the RASA size, it will use cameras under a certain diameter before it obstructs the corrector plate. The RASA is currently only built by Celestron.
The speed of these Astrograph scopes compared to other scopes is extreme and these scopes were not designed for beginners! There is a review and comparison between the RASA 8 and SW 72 ED Pro in the review section (along with pros and cons).
Recommended for starters
For beginners, it is recommended to purchase a basic scope which is cheap and expendable in case the hobby is not for you, or you have minimal time and/or budget. There will be some cheap second-hand scopes on eBay and related sites which sell equipment like this.
If you feel the need to upgrade this, the next scope for visual use is a Dobsonian-style scope. 6” or 8” and it comes with eyepieces. Beginners and advanced observers can use the Dobsonian telescope either with or without go to capability and to top it off... it is cheap! My first scope was a 10” Skywatcher flex-tube Dobsonian scope which was purchased in the memory of my grandad. I still have this scope and for visual, it cannot be beaten.
After this, your options are open depending on where you want to go! Whether it be Astrophotography or purely visual there is multiple routes you can take depending on your budget and how deep you want to go down the rabbit hole, as they say.
Don't be forced into rushing. Ask for help in local groups, which will no doubt give options for multiple scopes and mounts - but at the end of the day, it is up to you, as it will be with your money.
For beginners, it is recommended to purchase a basic scope which is cheap and expendable in case the hobby is not for you, or you have minimal time and/or budget. There will be some cheap second-hand scopes on eBay and related sites which sell equipment like this.
If you feel the need to upgrade this, the next scope for visual use is a Dobsonian-style scope. 6” or 8” and it comes with eyepieces. Beginners and advanced observers can use the Dobsonian telescope either with or without go to capability and to top it off... it is cheap! My first scope was a 10” Skywatcher flex-tube Dobsonian scope which was purchased in the memory of my grandad. I still have this scope and for visual, it cannot be beaten.
After this, your options are open depending on where you want to go! Whether it be Astrophotography or purely visual there is multiple routes you can take depending on your budget and how deep you want to go down the rabbit hole, as they say.
Don't be forced into rushing. Ask for help in local groups, which will no doubt give options for multiple scopes and mounts - but at the end of the day, it is up to you, as it will be with your money.
Budget limits (assumed and based on new components – visual only)
£500 and under
This leaves little to no room and the only and best choice is the Dobsonian scope. The best option and you have options for a few different sizes. 8” Dobsonian goes for roughly £375 or the 10” which is slightly over budget at £539. The 6” also comes in at £295. All three of these are solid tube Dobsonian scopes.
£1000 and under
Again the Dobsonian is a very good choice, again with more options for an Aperture up to 300mm non-motorised mount or the SW 200p motorised mount. Other options are a Smaller reflector scope and a basic mount in the means of SW 150PL and SW EQ5 Pro GOTO mount. This will enable tracking of objects and slewing to targets easier with computer-assisted tracking. If you are not concerned about tracking and slewing to targets and are happy to find targets manually, then the Dobsonian light buckets are still the best and cheapest options.
Budgets higher than this is beyond this page as this is aimed at people starting in Astronomy and are looking for visual only. Generally, people switch from visual to AstroPhotography and it's possible to take pictures with any scope, but some excel at it and some others are designed for AP (but with visual in mind). The budget of £1500 may be enough to get started in AP if you have some equipment (Camera, laptop, etc.). But to start in Astronomy, only a small budget is needed and enough to get a Dobsonian telescope to start enjoying the night sky.
£500 and under
This leaves little to no room and the only and best choice is the Dobsonian scope. The best option and you have options for a few different sizes. 8” Dobsonian goes for roughly £375 or the 10” which is slightly over budget at £539. The 6” also comes in at £295. All three of these are solid tube Dobsonian scopes.
£1000 and under
Again the Dobsonian is a very good choice, again with more options for an Aperture up to 300mm non-motorised mount or the SW 200p motorised mount. Other options are a Smaller reflector scope and a basic mount in the means of SW 150PL and SW EQ5 Pro GOTO mount. This will enable tracking of objects and slewing to targets easier with computer-assisted tracking. If you are not concerned about tracking and slewing to targets and are happy to find targets manually, then the Dobsonian light buckets are still the best and cheapest options.
Budgets higher than this is beyond this page as this is aimed at people starting in Astronomy and are looking for visual only. Generally, people switch from visual to AstroPhotography and it's possible to take pictures with any scope, but some excel at it and some others are designed for AP (but with visual in mind). The budget of £1500 may be enough to get started in AP if you have some equipment (Camera, laptop, etc.). But to start in Astronomy, only a small budget is needed and enough to get a Dobsonian telescope to start enjoying the night sky.