Thinking About a New Scope? Think Big!


Made in the USA



25" f/5 & f/4 Classic

25" f/5 Classic Obsession

Dave Kriege with Obsession #2 built in 1989.

25" f/4 Classic Obsession

25" f/4

Chaco Observatory at Chaco Culture National Historical Park in northwestern New Mexico's San Juan Basin.

25" Classic Obsession

25" (customized)

Custer Institute and Observatory - Southold, NY

M13 comparison


25" f/5 Classic Obsession

Andrew L - Perth Australia

25" f/4

Forget averted vision. Globulars, nebulae, and galaxies will come screaming out of the eyepiece.

You won't believe your eyes. This is the cure for aperture fever!

Join the realm of Herschel whose famous NGC catalog of deep sky object descriptions are exactly what you will experience.

This is the telescope that Dave Kriege, founder of Obsession, uses for his personal observing.

The Obsession 25 is considered to be the ultimate telescope for the serious deep sky astronomer who can afford the best.

One person set up, one handed guiding, one incredible observing machine.

Try direct vision - you'll get used to it.

Advantages of f/4

10 times the light gathering power of an 8 inch Schmidt-Cassegrain Obsession
Limiting stellar magnitude: 17 14.0
Rayleigh Resolution Limit: 0.22
arc seconds
arc seconds
Contrast limit:
(minimum diameter before a
nebular object fades from view)
arc minutes
arc minutes

Customer Comments

Paul W., 25" owner at OzSky Star Party - April 9, 2014

An exceptional view of the Homonculus Nebula surrounding Eta Carinae. I've noted in the past that this object is the only one that resembles its Hubble Telescope image. It more than resembled its Hubble view this week. It was at least as detailed, if not more, in the eyepiece of the 25" Obsession. I've seen this object on my three previous visits to OzSky, but never before like this.
Paul W.

Tim Conners, 25" owner in Statesboro, Georgea
April 22, 2013

Jon Isaacs 25" Obsession

Dave, Shot these last night with my 25-inch f/5 and iPhone 4S. Used a Baader 90+ percent neutral density filter on my 31 mm Nagler for the Moon photo and just a little post-processing in Aperture.

I'm no astrophotographer, but the Moon shot rivals those in the magazines.

I put a 2.5x Powermate on my 6 mm Ethos for a magnification of 1300x on the Moon. The air would calm every minute or so and I'd get goosebumps from the views. I had to be resolving surface features less than a mile in diameter with that setup.

Tim Conners

Tim C., 25" owner in Statesboro, Georgia - March 19, 2013

Maria Conners

I wanted you to know that my 13 year old daughter, Maria, just took the top award in her school's science fair competition, measuring the orbits of a handful of double stars with my new 25-inch. She had a blast. The judges loved it. And Dad couldn't be happier... Tim C.

Read more 25" customer comments


Currently the largest public telescope in Chile... (June 2015). The Observatorio del Pangue stands atop a moderate hill in a mountainous landscape close to the Elqui Valley, located some 480 km (300 mi.) north of the capital city Santiago de Chile.


by Dan Price

NGC 891

NGC 891
by Bob Brunck


by Bob Brunck


by Antonio Roman

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25" Specifications:

Metric info shown in italics

Primary Mirror:

  • 25" - 635 mm f/4 OMI 2 inch thick mirror
  • Fused silica glass standard on all 25" 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
  • f/4: 4.0" - 102 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:

  • f/4: 100" (± 2") - 2,540 mm (± 50 mm)

Eyepiece Height at Zenith:

  • f/4: (approximately) 8' - 245 cm

Mirror Cell:

  • 18-point

Truss Pole:

  • f/4: Length: 70" (± 2") - 180cm (± 5 cm)
  • Diameter: 1.5" - 38 mm
  • Wall Thickness: 0.049" - 1.2 mm

Upper Assembly:

  • Diameter: 30" - 76 cm
  • Height: 16" - 40.5 cm
  • Weight: f/4: 16 lbs. - 7.2 kg

Lower Assembly:

  • A= 35" - 89 cm | B= 35" - 89 cm | C= 28" - 71 cm | D= 32" - 81 cm

see diagram

Mirror Box weight:

  • The heaviest component (what you don't lift): 150 lbs - 68 kg
  • Weight at Handles: (what you lift at Wheelbarrow handles): 40 lbs - 18 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

All 15”, 18 and 25” 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.


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 ($8,000 for 25" 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.