Obsession Telescopes
Obsession Telescopes are legendary among visual astronomers for one simple reason: they deliver breathtaking views. Built in the USA and trusted by serious observers worldwide, Obsession Dobsonians are designed with precision optics, rock-solid mechanics, and a focus on pure visual performance.
Learn more about Obsession Telescopes at obsessiontelescopes.com .
Why Aperture Matters
When choosing a telescope, many beginners focus on magnification — but magnification is one of the least important specifications. What truly matters is aperture: the diameter of the telescope’s primary mirror.
Aperture determines how much light a telescope can gather. More light means fainter objects become visible, details in galaxies and nebulae stand out, and planets reveal finer structure. A larger aperture also improves resolution, allowing the telescope to separate closely spaced details that smaller instruments simply cannot resolve.
Magnification can always be increased with different eyepieces, but no eyepiece can make up for insufficient aperture. This is why large Dobsonian telescopes like these Obsessions excel under dark skies — they show the universe as it truly is.
25-inch f/5 Obsession Classic
Name: Not yet named
Aperture: 25 inches (635mm)
Focal Ratio: f/5
Focal Length: 3175mm
Height at Zenith: ~11 feet
Limiting Magnitude: 17+
Rayleigh Resolution: 0.22 arcseconds
Tracking: ServoCAT system
Owner: Kyle
This massive 25-inch Obsession delivers astonishing deep-sky views and,
with ServoCAT tracking, effortlessly follows objects across the sky —
perfect for extended observing sessions and public outreach.
25-inch f/5 Obsession Classic
Name: The Lighthouse
Aperture: 25 inches (635mm)
Focal Ratio: f/5
Focal Length: 3175mm
Height at Zenith: ~11 feet
Limiting Magnitude: 17+
Rayleigh Resolution: 0.22 arcseconds
Owner: James
Aptly named The Lighthouse, this telescope pulls faint galaxies
and nebulae out of the darkness, acting as a beacon under truly dark skies.
22-inch f/4.2 Obsession Ultra Compact
Name: Not yet named
Aperture: 22 inches (559mm)
Focal Ratio: f/4.2
Focal Length: 2350mm
Height at Zenith: 7 ft 4 in
Limiting Magnitude: 16.7
Rayleigh Resolution: 0.25 arcseconds
Owner: Kyle
The Ultra Compact design delivers serious aperture in a more manageable,
observer-friendly package — without sacrificing optical performance.
18-inch f/4.5 Obsession Classic
Name: Name: Little John
Aperture: 18 inches (457mm)
Focal Ratio: f/4.5
Focal Length: 2060mm
Height at Zenith: 6 ft 5 in
Limiting Magnitude: 16
Rayleigh Resolution: 0.31 arcseconds
Owner: James
Compact, powerful, and easy to use — Little John punches far above its size
and is a favorite for both personal observing and outreach.
15-inch f/4.5 Obsession Classic
Name: Name: Not yet named
Aperture: 15 inches (381mm)
Focal Ratio: f/4.5
Focal Length: 1727mm
Height at Zenith: 5 ft 5 in
Limiting Magnitude: 15.5
Rayleigh Resolution: 0.36 arcseconds
Owner: Kyle
A fantastic balance of aperture, portability, and performance — ideal for
observers who want serious views without climbing ladders.
Understanding the Specifications
- Aperture: The diameter of the primary mirror — larger means more light and finer detail.
- Focal Ratio (f/): Determines how “fast” the telescope is; lower numbers mean wider fields and shorter tubes.
- Focal Length: Affects magnification and field of view when paired with eyepieces.
- Eyepiece Height: How high the observer’s eye is when the telescope points straight up.
- Limiting Magnitude: The faintest stars visible under ideal dark-sky conditions.
- Rayleigh Resolution: Theoretical ability to separate close details — smaller numbers are better.