Thinking About a New Scope? Think Big!


Made in the USA



18" f/4$8,495

Plus Shipping & Crating

Just your size. Large Aperture, no big ladder needed! Our most popular model.

The Obsession 18" is the ultimate compact scope for the discriminating enthusiast who wants big aperture in a small package.

There are no short cuts in construction or performance.

The Obsession 18" features the same quality craftsmanship and award winning design as found on our renown 20, 25, 30 and 36 inch telescopes.

A small step ladder is required when the scope is pointed near the zenith but most observing will be done with your feet on the ground.

We've done our homework - the 18" is easy to set up and a joy to use.

Fantastic deep sky and planetary images.

One look and you'll re-learn what it means to be excited about astronomy.

5 times the light gathering power of an 8 inch Schmidt-Cassegrain Obsession
Limiting stellar magnitude: 16 14.0
Rayleigh Resolution Limit: 0.31
arc seconds
arc seconds
Contrast limit:
(minimum diameter before a
nebular object fades from view)
arc minutes
arc minutes

Customer Comments

Ted Forte, 18" owner in Virginia Beach, Virginia

Ted Forte

My Obsession 18" is about to turn 11 years old. It's a little battle-scarred, a veteran of many, many, observing sessions, star parties and outreach events, but it still looks and performs great. I have logged thousands of objects with it, but more importantly, I have shared the heavens with more than 20,000 souls through it. I can truthfully say it is the best purchase I have ever made. I often tell novice astronomers that there is no perfect telescope – but the Obsession 18" comes pretty close.

Ted Forte is chair of the Astronomical League's Planetary Nebula Club. He has written "Flowers of the Night Sky" in the June 2010 issue of Sky & Telescope magazine. Watch for his next S&T article on exploring the Virgo-Coma galaxy cluster which will appear in the May 2011 issue.

Read more 18" customer comments


by Johannes Brachtendorf


by Mikael Svalgaard


by Todd Kozikowsk


by Johannes Brachtendorf


by Ernesto Gonzalo de Luis


by Todd Kozikowsk

NGC 4656

NGC 4656
by Johannes Brachtendorf


by Javier Jovani


by Todd Kozikowsk


by Jerry Pinter


by Javier Jovani


by Todd Kozikowsk

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18" Specifications:

Metric info shown in italics

Primary Mirror:

  • 18" - 457 mm Ostahowski, or OMI 2 inch thick mirror
  • Fused silica glass standard on all 18" Classic primary mirrors.
  • 96% reflectivity
  • Enhanced Aluminum Coating and Dielectric Overcoat (a supreme coating)
  • Center marked for precise collimation
  • plus Interferometry certification

see Optics page for more info

Secondary Mirror:

  • Pre-installed
  • 3.1" - 79 mm United Lens 1/10 wave or better
  • Interferogram included
  • 96% reflectivity at 550 nm
  • Super enhanced Brilliant-Diamond non-fading multi-dielectric coating

see Optics page for more info

Focal Length:

  • 75" (± 2") - 1900 mm (± 50 mm)

Eyepiece Height at Zenith:

  • (approximately) 71" - 180 cm

Mirror Cell:

  • 18-point

Truss Pole:

  • Length: 49" (± 2") - 140 cm (± 5 cm)
  • Diameter: 1.25" - 32 mm
  • Wall Thickness: 0.035" - 0.9 mm

Upper Assembly:

  • Diameter: 22" - 56 cm
  • Height: 12" - 30 cm
  • Weight: 9 lbs. - 4.1 kg

Lower Assembly:

  • A= 26" - 66 cm | B= 27" - 68 cm | C= 21" - 53 cm | D= 25" - 63 cm

see diagram

Mirror Box weight:

  • The heaviest component (what you don't lift): 80 lbs - 36 kg
  • Weight at Handles: (what you lift at Wheelbarrow handles): 18 lbs - 8 kg

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Standard Features and Accessories:

Choose from four great focusers

The JMI EV3 comes standard on all Classic Obsessions. Or upgrade to the EV1, or EV1 with motofocus, or the awesome Feathertouch by Starlight Instruments. See the Focuser Options page for more information.


JMI EV3 (standard on all Classics)

JMI EV1 with motofocus

JMI EV1 with motofocus



Feathertouch by Starlight Instruments

by Starlight Instruments

Wheelbarrow handles

Comes standard on all Obsessions 12.5" through 25" at no extra charge.

Primary Mirror Coating

Enhanced Aluminum - 96% reflectivity, with dielectric overcoat (a supreme coating) standard on all primary mirrors. See Optics page for more info.

Secondary Mirror Coating

An Obsession exclusive - Super enhanced Brilliant-Diamond is standard on all Obsession secondary mirrors. This premium multi-dielectric coating has 96% reflectivity at 550 nm. The ultimate coating for the deep sky obsessed. This coating is standard on all Obsession secondaries at no extra charge. Brilliant-Diamond is just one of the reasons Obsessions out perform all others.

With 96% enhanced on the primary and our standard 96% Brilliant Diamond secondary, the optical system is equivalent to an extra 2" of aperture!

12 volt cooling fan

telescope mirror cooling fan

12 volt cooling fan comes standard on all Classic and Ultra Compact scopes.

Fused quartz

18” Obsessions use fused quartz for the primary mirror glass.

more info

Optional Accessories:

See the Accessories page for more info on these items

Counterweight kit

(you supply the lead shot or sand) Recommended if you intend to use heavy barlow/eyepiece combinations, a Paracorr coma corrector, a traditional finderscope, or the Argo Navis digital setting circles.



$450 (Highly recommended at f/4.2)

Ripstop Nylon light shroud

Barlow-Laser Collimator 2" barrel

(Highly recommended). Includes 2" magnetic barlow lens and mask for the new barlowed laser collimating technique. Great visual aid and no better way to accurately align fast Newtonians. learn how

Argo Navis digital setting circles
with ultra res 32K encoders

more info

ServoCAT Goto Drive System

more info

Dew heater for secondary mirror

Secondary mirror heating system automatically senses the air temperature and the mirror temperature, then maintains the secondary at a preset (adjustable) temperature above the ambient air temperature to prevent dewing or icing.

Pre-installed (if ordered).

more info

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Ordering Information:

A Deposit is required to place an order ($2,000 for 18" Classic)

Mail the deposit to:

Obsession Telescopes
PO Box 804
Lake Mills, WI 53551

You can e-mail your order, or mail it with the deposit.

  • With your order, please list any options and/or accessories you want, your mailing address, e-mail address if any, and phone number(s).
  • After we receive it, we will send you an order confirmation letter.
  • Delivery is usually 1 to 2 months from time of order.
  • Please e-mail for current delivery times.
  • Balance due prior to shipment.
  • Prices do not include shipping and crating. We ship throughout the world via UPS.
  • Any questions, please call or e-mail.
  • NOTE 10% order cancelation charge.