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18" UC Obsession

18" UC Obsession


18" f/4.2 UC (Ultra Compact)

18" UC

"The Obsession 18" UC continues to perform, season-after-season, with over-the-top views of the sky. I just can't say enough about its ease of set-up, spot-on collimation, and precision observation at the eye piece. It has become a star party favorite, and a tremendous personal telescope. It is a brilliant instrument, and I owe a great amount of thanks to Dave Kriege for this extraordinary creation! It is the ultimate in portability, ease of usage and deep-sky observing. It performs among the giants in this industry."

Boyd Levet
Sisters, Oregon

  • Collapsed, the base is 25" x 25" x 13.5" high
  • Weight of heaviest component is 72 pounds
  • Eyepiece height at zenith is 5 feet 10 inches
  • See more Specifications

18" UC includes:

M13 comparison

Astronomy magazine

Cloudy Nights


18" f/4 UC $8,495

Plus Shipping & Crating

2X the light gathering power of a 12.5"

The 18" f/4 UC (Ultra Compact) is a revolutionary design. It is a large aperture telescope that collapses into a very small package. If you have limited hauling or storage capacity, (like the trunk of a small car) then this is the scope for you.

18" UC Virtual Mirror Box

Our revolutionary Virtual Mirror Box (VMB) is the foundation of the UC design. It is a welded steel framework made from NC laser cut steel. It provides four main functions. It provides the primary mirror cell, the altitude bearings, the connection points for the truss poles, and a retainer for the wheelbarrow handles. To keep it as ultra compact as possible, the side bearing portion is foldable to reduce the height of the VMB by half.

In the transport mode the clearance height is a mere 14 inches. Or place the VMB (Virtual Mirror Box) next to the rocker in your car and reduce the height even more. Now everyone can have a big aperture scope and take it to their dark sky site. This telescope will appeal to those that like the ultimate in form follows function style. Lower eyepiece height means 90% of observing will be done with your feet on the ground. The UC is all black with a modern space frame construction. If your vehicle is small or you intend to put it in the trunk, then the Ultra Compact is the obvious choice. And if you want the ultimate in Dobsonian evolution, the Obsession Ultra Compact 18" is it.

Sky & Telescope Hot Product 2008

No compromises. The UC uses the same proven design criteria and materials that made the Classic Obsession so successful and the most copied larger aperture dob on the market. We use the same premium optics from Ostahowski and OMI that we do in our Classic series of telescopes. Diffraction limited and all figured and tested with interferometry. Ion deposition 96% enhance primary coating. Two inch flex free glass. One tenth wave 96% Diamond brite secondary mirror. As with our Classic series, you cannot get better optics at any price anywhere. Ostahowski and OMI are so confident of their quality that they post the serial number and test data for ever mirror they make on their web sites for everyone to review. Nobody else does this.

5 times the light gathering power of an 8 inch Schmidt-Cassegrain Obsession
18" UC
Limiting stellar magnitude: 16.0 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

Jeffrey Kaszczuk, 18" UC owner in northeast Texas
February 27, 2012

Jeffrey Kaszczuk

Brief "first light" in my back yard last week, M42 and Jupiter. Then, we took the scope to our dark sky spot in the Caddo National Grassland in northeast Texas. Brought along a buddy with his 12" Skywatcher. His Skywatcher sat alone and unused all night. I couldn't peel him away from my scope HAHAHAHA!!! The feathertouch focuser is awesome. The entire scope is awesome. Once the crescent moon, Jupiter and Venus set, we started our galaxy hunting. Best one of the night was M51. I AM VERY, VERY, VERY SATISFIED WITH THIS TELESCOPE. Thanks Dave!! My friends may be contacting you about making one for them!! Some pics attached.

Eric Recurt

Never out without my 18" UC - Eric Recurt in France

Raanan Yechezkel

Hi Dave,
Had to take our smaller car this time. Here’s my 18UC in a Seat Ibiza (a very small car) with camping equipment. It truly is very compact!
Raanan Yechezkel - Israel

Read more 18" UC customer comments

18" UC Photos

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photos courtesy of Astronomy Magazine and Gary Kopff

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18" UC vs 18" Classic

Obsession 18" UC

Obsession 18" Classic

Eyepiece height at zenith 67 inches 71 inches
Set up time including nylon light shroud Same for both
Ease of use (setup, take down, collimation) Same for both
Ease of Motions (hand guiding) Same for both
Construction/materials Same for both, except:
components covered with satin black laminate components are stained and have six coat polyurethane finish
Bearing geometry and surfaces Same for both, Ebony star on etched virgin Teflon
Light baffling Classic is better with 360 degree upper tube assembly baffle. UC 160 degree baffle opposite focuser. Views and contrast are identical unless there is a nearby street light in the area. If you only observe in the city at home then the Classic is the better choice. If you like to take your scope to a dark site the UC is an excellent choice, especially if you drive a sedan or have limited transport space.
Optics (OMI) (Ostahowski does not offer anything under 18 inches) Same for both.
f/4.2 primary mirror - requires a Paracorr coma corrector for optimum views.
Fused silica glass standard on all 18" UC and Classic primary mirrors.
Secondary mirror Same 3.1 secondary mirror for both. Central obstruction and image contrast the same for both under good skys.
Coatings Same for both. 96% on primary, 96% on secondary
Mirror cell Same for both, 18 point
Wheelbarrow handles Standard on both
Truss poles Six 1.25 inch diameter. Connected in pairs at apices. Eight 1.25 inch diameter. All eight separate.
Stability UC has 6 pole design and Baltic Birch steel reinforced segmented bearings. Much less mass than Classic. Eight pole design and one piece cast aluminum side bearings. Mirror box and rocker have more mass. Total weight is about 50 pounds heavier than the UC. Classic is a better choice for CCD imaging.
Dimensions for transport 24" x 25" x 12" high. Includes virtual mirror box nested in rocker (will fit in most trunks or hatchback). 27" x 27" x 26" high (rocker and mirror box) Upper tube assembly placed next to lower unit.
Upper Tube Assembly weight (with Feathertouch focuser) 8 pounds 11 pounds
Weight of heaviest component (includes 2 inch thick standard thickness mirror) 72 pounds. Includes the virtual mirror box, mirror, and dust cover 82 pounds Includes mirror box, mirror, and dust cover.
Weight at wheelbarrow handles about 10 pounds about 15 pounds
Weight of complete scope about 90 pounds about 140 pounds
Clearance width required with wheelbarrow handles attached.
(or minimum size of doorway needed to roll in or out with wheels attached)
29 inches

Clearance width needed when carrying UC virtual mirror box is 28 inches.
30 inches

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18" UC 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" UC 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") - 1905 mm (± 50 mm)

Eyepiece Height at Zenith:

  • (approximately) 70" - 178 cm

Mirror Cell:

  • 18-point

Truss Pole:

  • Length: 55" (± 2") - 140 cm (± 5 cm)
  • Diameter: 1.25" - 32 mm
  • Wall Thickness: 0.035" - 0.9 mm

Upper Assembly:

  • Diameter: 22" - 56 cm
  • Height: 13.5" - 34 cm
  • Weight: 6 lbs. - 2.7 kg

Lower Assembly:

  • Virtual Mirror Box stacked in Rocker for Transport
    24" x 25" x 22" high

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Standard Features and Accessories:

Feathertouch focuser by Starlight Instruments

Feathertouch on UC

Standard on all Ultra Compacts

Low profile, Crayford type, 2 inch focuser, with 1-1/4 inch threaded adaptor for filters. Compression rings. Can be swiveled on it's base to the most convenient position. A joy to use and beautiful to look at.


Standard on all Ultra Compacts

External light baffle

Standard on all Ultra Compacts

Counterweight kit

Standard on all Ultra Compacts

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

more info

Optional Accessories:

See the Accessories page for more info on these items


$475 (Highly recommended at f/4.2)

Ripstop Nylon light shroud

(Highly recommended)

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" UC)

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.