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

15-inch Telescopes (381mm)

A 15-inch aperture offers a light-gathering power 4 times that of an 8-inch Schmidt-Cassegrain telescope. Amateurs will get amazing detailed views of the deep night sky objects with it. Obscure galaxies will appear with real color and details. However, there are not many options for a 15-inch telescope available on the market. Obsession Ultra Compact (UC) 15-inch Dobsonian is the only scope with a 15-inch aperture. It is great for astrophotography and serious astronomy.

What is a 15-inch telescope?

A 15-inch telescope refers to a telescope having an aperture (the diameter of the objective lens) of 15-inch (381 mm). A 15-inch telescope is considered to be in the category of large telescopes. For example, Obsession Ultra Compact (UC) 15-inch Dobsonian is for now the only 15-inch scope available on the market.

What can you see with a 15-inch telescope?

  • The Moon and craters with clear details.
  • The phases of Venus.
  • The moons of Jupiter, the Great Red Spot, the Cassini Division, etc.
  • The polar ice caps on Mars.
  • The rings of Saturn.
  • Uranus and Neptune with their bluish color.
  • The galaxies in Virgo Cluster or Ursa Major.

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

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