3-inch Telescopes (76-94mm)

What is a 3-inch telescope?

A 3-inch telescope is a type of small-size telescope that has an aperture (the diameter of the objective lens) of 3-3.75 inch (76-94 mm). The aperture size determines the light-gathering power and resolution of the telescope, with larger apertures collecting more light and providing clearer images. 3-inch telescopes are ideal for kids and beginner astronomers due to their manageable size and capabilities. They offer a range of focal ratios from f/3.9-f/12 and an average focal length between 300-900 mm, which affects the magnification and field of view of the telescope. The highest magnification achievable with a 3-inch telescope is 152-189x times the human eye, which is suitable for observing celestial objects like Venus and its phases, the Moon with craters, Jupiter’s cloud bands, Saturn with rings, and various galaxies and nebulae. 3-inch telescopes can be found in different optical designs, such as Dobsonian, and are available in a wide price range, typically between 69-1,495$. They often come with a finder scope, which helps users locate objects in the sky by providing a larger field of view. Two important aspects not mentioned in the article are the resolving power and light-gathering power of a 3-inch telescope. The resolving power refers to the ability of the telescope to distinguish fine detail in objects, while the light-gathering power determines how bright the objects appear in the eyepiece. Lastly, when compared to larger telescopes, such as 4-inch, 5-inch, 6-inch, or 7-inch models, 3-inch telescopes have lower aperture, focal length, and magnification capabilities. However, they remain a popular choice for beginners and casual astronomers due to their portability, affordability, and ease of use.

What is a 3-inch refractor telescope?

A 3-inch refractor telescope is a type of telescope that uses an objective lens with a diameter of 3 inches (approximately 76 millimeters) to gather light and focus it for viewing celestial objects. The primary components and attributes of a 3-inch refractor telescope are the aperture, objective lens, focal length, eyepieces, mount, and price range.

The aperture of a 3-inch refractor telescope is 3 inches (76 mm), determining the amount of light the telescope can collect and the level of detail it can resolve in celestial objects. The objective lens, the main lens of the telescope used to collect and focus light from celestial objects, has a diameter of 3 inches (76 mm) in a 3-inch refractor telescope. The focal length can vary depending on the specific model, but the average is approximately 11.8 inches (300 mm). Eyepieces are used to view celestial objects through the telescope and come in different focal lengths, determining the magnification and field of view. A 3-inch refractor telescope can have either an azimuth or equatorial mount. An azimuth mount allows the telescope to move up and down and left to right, while an equatorial mount tracks the rotation of the Earth along a single axis, making it easier to follow celestial objects as they move across the sky. The price range for 3-inch refractor telescopes is typically between $70 and $500, with telescopes priced around $200 offering the best value for money with a good balance of quality and features.

The average magnification power of a 3-inch refractor telescope is approximately 150x, although this can vary depending on the specific eyepiece used. The telescope may also include a finder scope, a small telescope attached to the main telescope used to locate and center celestial objects before viewing them through the main telescope. A dew shield, an accessory that helps prevent dew formation on the optics of the telescope and reduces unwanted reflections, improving contrast during viewing, may also be included.

In addition to these primary components and attributes, there are several other factors to consider when choosing a 3-inch refractor telescope. These include the weight and length of the telescope, which can affect its portability and ease of use, particularly for younger users or those who travel frequently for stargazing. A carrying case is an essential accessory for protecting the telescope during transportation and storage.

It is also helpful to compare a 3-inch refractor telescope with other telescope types (e.g., reflector or compound) and different sizes within the refractor category to understand the advantages and disadvantages of this particular size and type.

What is a 3-inch reflector telescope?

A 3-inch reflector telescope is a small and portable telescope with an aperture (the diameter of the primary mirror) of 3 inches (76mm) that gathers and reflects light to a focal point for viewing. It has a moderate light-gathering ability and a maximum magnification of approximately 150x. The typical field of view for a 3-inch reflector telescope is around 1-2 degrees.

Equatorial mounts, Dobsonian mounts, and Alt-Azimuth mounts are recommended for a 3-inch reflector telescope, with the choice depending on individual preferences and requirements. The purpose of the optical design in a 3-inch reflector telescope is to create lenses with specific properties using optical lens design and optical glass, and to allow for a three-dimensional image to be viewed through the use of binoculars.

The ideal focal ratio for a 3-inch reflector telescope is f/10, and the ideal focal ratio for a 3-inch reflector telescope is approximately f/5. Double stars, galaxies, clusters, and nebulae are the best celestial objects to observe with a 3-inch reflector telescope.

What can you see with a 3-inch telescope?

A 3-inch telescope is a portable and relatively affordable telescope that allows you to observe stars, planets, and some deep space objects such as galaxies and nebulae. With this telescope, you can see Venus and its phases, the Moon with craters, Jupiter’s cloud bands and the Great Red Spot, Saturn with rings, M 31 and M 33, NGC galaxies, and nebulae like M 42, M 8, etc.

Types and Technical Specifications of 3-inch telescope

Types (Optical Design)

Dobsonian: Example: Orion FunScope 76mm Tabletop Dobsonian f/3.9 Telescope Kids Kit

Newtonian: Example: Celestron AstroMaster LT 76AZ Telescope, Celestron FirstScope Telescope, Celestron Cometron FirstScope 76 Telescope, Celestron FirstScope Signature Series Moon by Robert Reeves, Celestron National Park Foundation FirstScope f/3.9 Newtonian Reflecting Telescope, Orion SpaceProbe II 76mm f/9.2 Newtonian Reflecting Telescope

Maksutov Cassegrain: Example: Orion FunScope 76mm Tabletop Dobsonian Reflector Telescope, Sky-Watcher Virtuoso Versatile Alt-Azimuth Mount

Doublet Refractor: Example: Explore Scientific Firstlight AR90mm White Tube Refractor W/ AZ Mount, Celestron AstroMaster 80AZ Refractor Telescope, Celestron Astro Fi 90 mm WiFi Refractor, Sky-Watcher Evolux 82ED Doublet APO Refractor, Celestron StarSense Explorer LT 80AZ Smartphone Telescope, Celestron PowerSeeker 80AZS Telescope, Takahashi Starbase 80 f/10 Doublet Refracting Telescope, Explore Scientific FirstLight 80mm Refractor with Twilight Nano Mount, Explore Scientific FirstLight 80 mm GoTo Refractor Package, iOptron 80mm Refractor, William Optics Super ZenithStar 81 Doublet Refractor Telescope – Astrophotography Package – Red & Gold, Celestron 80LCM Computerized Telescope, Vaonis STELLINA Smart Telescope, Orion ST80-A Refractor Astro Version w No Case, Orion ST80-T Refractor Terrestrial Version w No Case, Orion ST80 Refractor OTA, Orion CT80 Compact f/5 Doublet Refracting OTA Telescope

Triplet Refractor: Example: Sharpstar 94mm f/5.5 ED Triplet Apo Refractor Telescope, William Optics Gran Turismo 81 APO Triplet Refractor Telescope – Gold, Gray, Red, Orion Grab-n-Go 80mm f/6 Triplet Refracting Telescope

Technical Specifications

Aperture: 3-3.75 inch (76-94 mm)

Focal Length: 300-900 mm 

Focal ratio: f/3.9-f/12

Highest Magnification: 152-189x

Light Gathering Power: 118-131x

Price: 69-1,495$

Images taken with 3-inch telescopes

Examples of 3-inch telescopes

3-inch

• Orion FunScope 76mm Tabletop Dobsonian Reflector Telescope
• Celestron AstroMaster LT 76AZ Telescope
• Celestron FirstScope Telescope
• Celestron Cometron FirstScope 76 Telescope
• Orion FunScope 76mm Tabletop Dobsonian f/3.9 Telescope Kids Kit
• Celestron FirstScope Signature Series Moon by Robert Reeves
• Celestron National Park Foundation FirstScope f/3.9 Newtonian Reflecting Telescope
• Orion SpaceProbe II 76mm f/9.2 Newtonian Reflecting Telescope

3.25-inch 

• Orion Grab-n-Go 80mm f/6 Triplet Refracting Telescope
• Orion ST80 Refractor OTA
• Orion CT80 Compact f/5 Doublet Refracting OTA Telescope
• Celestron Travel Scope 80 Portable Telescope with Backpack
• Celestron AstroMaster 80AZ Refractor Telescope
• Sky-Watcher Evolux 82ED Doublet APO Refractor
• Celestron StarSense Explorer LT 80AZ Smartphone Telescope
• Orion ST80-T Refractor Terrestrial Version w No Case
• Orion ED80T Carbon Fiber ED APO Refractor Telescope
• Takahashi Starbase 80 f/10 Doublet Refracting Telescope
• Explore Scientific FirstLight 80mm Refractor with Twilight Nano Mount
• Explore Scientific FirstLight 80 mm GoTo Refractor Package
• iOptron 80mm Refractor
• William Optics Super ZenithStar 81 Doublet Refractor Telescope – Astrophotography Package – Red
• Celestron 80LCM Computerized Telescope
• Celestron PowerSeeker 80AZS Telescope
• William Optics Gran Turismo 81 APO Triplet Refractor Telescope – Gold, Gray, Red
• Vaonis STELLINA Smart Telescope
• Orion ST80-A Refractor Astro Version w No Case

3.5-inch

• Explore Scientific Firstlight AR90mm White Tube Refractor W/ AZ Mount
• Celestron Astro Fi 90 mm WiFi Refractor
• Sky-Watcher Virtuoso Versatile Alt-Azimuth Mount

3.75 inch

• Sharpstar 94mm f/5.5 ED Triplet Apo Refractor Telescope

How do 3-inch telescopes compare to other size-telescopes

3-inch vs 4-inch telescopes

3-inch telescopes provide focal lengths of 300-900 mm ( f/3.9-f/12), while 4-inch telescopes vary in focal lengths from 450-1350 mm (f/3.9-f/9). 3-inch telescopes provide the highest magnification of 152-189x, whereas 4-inch telescopes can magnify 204-236x. 

3-inch vs 5-inch telescope

5-inch telescopes provide a focal length of 650-1900 mm with a focal ratio of f/5-f/15. In contrast, 3-inch telescopes vary from 450-1350 mm in focal length with a focal ratio of f/3.9-f/9. Moreover, 5-inch telescopes provide 225-260x the highest magnification, which is 152-189x in the case of 3-inch telescopes.

3-inch vs 6-inch telescopes

3-inch telescopes have less aperture than the 6-inch telescopes. They offer a focal ratio of f/3.9-f/10 whereas the 3-inch telescopes vary from f/3.9-f/12. However, 6-inch telescopes offer a focal length of 162-1800 mm. On the other hand, 3-inch telescopes vary from 300-900 mm in focal lengths. 6-inch telescopes provide the highest magnification of 295-320x, whereas 3-inch telescopes can magnify 152-189x. 

3-inch vs 7-inch telescopes

3-inch telescope has less aperture than the 7-inch telescopes. They offer a focal ratio of f/2.8-f/15 whereas the 3-inch telescopes vary from  f/3.9-f/12. Besides, 3-inch telescopes offer a focal length of 300-900 mm whereas the 7-inch telescopes start from 500 mm to 2700 mm mm in focal lengths. Moreover, 7-inch telescopes provide 360x the highest magnification, whereas 3-inch telescopes can magnify up to 152-189x.