Telescope Nerd » Sizes » 15-inch Telescopes (381mm)

15-inch Telescopes (381mm)

What is a 15-inch telescope?

A 15-inch telescope is a large optical instrument with an aperture of 381 mm (15 inches), allowing it to gather a significant amount of light for enhanced resolution and magnification capabilities. The focal length of a 15-inch telescope typically ranges from 1500 to 2000 mm, with an example like the Obsession Ultra Compact (UC) 15-inch Dobsonian having a focal length of 1600 mm and a focal ratio of f/4.2.

Truss Tube Dobsonian is the primary type of 15-inch telescope, with the Obsession UC model being a popular example. These telescopes often come with a FeatherTouch focuser and a Telrad finder. Weighing approximately 65 pounds (29.5 kg), a 15-inch telescope requires a sturdy mount, typically a Dobsonian mount, to ensure precise tracking of celestial objects.

With a light-gathering power 4 times that of an 8-inch Schmidt-Cassegrain telescope, a 15-inch telescope provides astronomers with a detailed view of the cosmos, including clear details of the Moon’s craters, the phases of Venus, the moons of Jupiter, and the rings of Saturn. It offers a field of view that allows for focused observations of specific celestial objects. Essential accessories for a 15-inch telescope include high-quality cameras, eyepieces, and filters to enhance the viewing experience.

What is a 15-inch refractor telescope?

A 15-inch refractor telescope is a powerful optical instrument that utilizes a large objective lens with a diameter of 15 inches to collect and focus light from distant celestial objects. This significantly enhances its light-gathering ability and resolution, providing brighter and more detailed views of astronomical phenomena. The telescope is mounted on an azimuth mount with sturdy construction, ensuring stability, precision, and ease of use. This mount minimizes vibrations for clear and steady observations and offers smooth tracking of celestial objects across the sky. A computerized control system provides automated object locating and tracking capabilities, making it accessible for users of various experience levels and simplifying the observation process. With a long focal length of 2000 mm, the 15-inch refractor telescope offers high magnification and detailed views of the night sky, allowing for close-up observations of celestial objects and revealing intricate details and structures. The telescope is equipped with quality optical glass, such as ED or apochromatic glass, delivering superior image quality with reduced chromatic aberration, making it ideal for astrophotography and serious astronomical observations.

What is a 15-inch reflector telescope?

A 15-inch reflector telescope is a powerful optical instrument designed for astronomical observation, offering a light-gathering power 4 times that of an 8-inch Schmidt-Cassegrain telescope. It features a large aperture that maximizes light-gathering capacity and resolution, making it ideal for observing faint celestial objects. The primary mirror of a 15-inch reflector telescope is typically made of glass with a silver coating, reflecting light to form clear images. With a focal length of approximately 380-400mm, this telescope offers a balance between magnification and field of view. The telescope’s dimensions include a tube length of 8 feet, impacting its size, portability, and performance. The 15-inch reflector telescope has a focal ratio of f/10, striking a balance between light-gathering power and magnification. Essential accessories for a 15-inch reflector telescope may include a stable mount, finder scope, and eyepieces.

What can you see with a 15-inch telescope?

A 15-inch telescope is a powerful instrument that offers excellent capabilities for detailed observation of celestial objects. Some of the best objects to observe with a 15-inch telescope include Beta Cygni, Messier 8, Messier 27, Messier 57, Messier 81 & Messier 82, Messier 13, Messier 31, h & χ Persei, and the Moon. A 15-inch telescope is capable of providing detailed views of deep-sky objects such as galaxies, nebulae, and star clusters, allowing amateurs to see real color and details of obscure galaxies.

Types and Technical Specifications of 15-inch telescopes


Truss Tube Dobsonian: Example: Obsession Ultra Compact (UC) 15-inch Dobsonian 

Technical Specifications

Aperture: 381 mm (15″)

Focal Length: 1600 mm

Focal ratio: f/4.2

Weight: ~65lbs

Focuser: FeatherTouch

Finder: Telrad

Price: 7,500$

Images taken with 15-inch telescopes

Photo: Obsession Ultra Compact (UC) 15-inch Dobsonian

Examples of 15-inch telescopes

  • Obsession Ultra Compact (UC) 15-inch Dobsonian Telescope

How do 15-inch telescopes compare to other size telescopes

15-inch vs 16-inch telescopes

Though the 15-inch telescope has less aperture than the 16-inch telescopes, it offers a focal ratio of f/4.2 whereas the 16-inch telescopes vary from f/10 to f/4.43. Besides, 15-inch telescopes offer a focal length of 1600 mm whereas the 16-inch telescopes start from 1800mm to 4064 mm in focal lengths.

15-inch telescopes16-inch telescopes
Aperture15-inch (381 mm)16-inch (406 mm)
Focal Ratiof/4.2f/10- f/4.43
Focal Length1600 mm1800-4064 mm

15-inch vs 17-inch telescope

15-inch telescopes provide a focal length of 1600mm, while 17-inch has a focal length of 2939mm. Besides, 15-inch telescopes cannot remove off-axis astigmatism and field curvature whereas 17-inch telescopes can eliminate them completely.

15-inch telescopes17-inch telescope
Aperture15-inch (381 mm)17-inch (432 mm)
Focal Ratiof/4.2f/6.8
Focal Length1600 mm2939 mm

15-inch vs 18-inch telescope

15-inch telescopes provide a focal length of 1600 mm. In contrast, an 18-inch scope is 1900mm in focal length though the focal ratio is the same. However, the price of the 18-inch scope is three times that of the 15-inch scope.

15-inch telescopes18-inch telescope
Aperture15-inch (381 mm)18-inch (457.2 mm)
Focal Ratiof/4.2f/4.2
Focal Length1600 mm1900 mm

15-inch vs 20-inch telescope

The 20-inch telescope has 125 mm more aperture than the 15-inch scope, which means it has more light gathering power than the 15-inch. Besides, the 20-inch scope has a focal length of 1826 mm( f/3.6) whereas 15-inch telescopes have a focal length of 1600 mm (f/4.2). But amazingly, the price range is very close.

15-inch telescope20-inch telescope
Aperture15-inch (381 mm)20-inch (508 mm)
Focal Ratiof/4.2f/3.6
Focal Length1600 mm1826 mm