Home / CN Report: The 18" f4.2 Obsession UC - Birth of a New Classic
by Tom Trusock 06/19/07 | Email Author
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The 18" f4.2 Obsession UC - Birth of a New
Albert Highe, Mel Bartels, Greg Babcock, John Hudek, and others have
spent years trying for
perfect portable dob. If you're active in the ATM scene,
you've had glimpses of several different lightweight designs,
but for us poor schmucks who don't know a hammer from a drill,
well, we're stuck dreaming. Yes, there's always
been trade offs for an ultra compact design: shroud coverage, flexture,
exposed mirror but for many of us the biggest is the lack of a major
vendor. Till now, if
you wanted a large aperture ultra compact scope you had some rather
Obsession Telescopes has been around for a
while. Owner Dave
Kriege has been given his due for his hand in the current dobsonian
and Obsession design is often imitated by ATM's. Some might not be too
happy about that, but Dave's attitude is just
the opposite - he helps where ever he can, even to the point of writing
how-to book and supplying parts to the do-it-yourself crowd.
The classic Obsession design grew out of a desire to make large
aperture telescopes portable, and there is no doubt it's weathered the
test of time quite well.
Unfortunately, city dwellers can attest that skies have gotten worse,
gas prices have increased, and the size of the average vehicle is
decreasing to cope. Yes, taking an 18" classic Obsession to a dark site
in a Prius is an entertaining thought, but reality is a bit more
Especially if like so many of us, you just don't seem to be getting any
So say hello to Dave's little friend: the Obsession 18 f4.2 Ultra
Compact or UC. The UC's aren't intended to replace the original
Obsession (henceforth referred to as the "Classic"), but they are an
to the product line for those who need an extremely portable
Obsession Telescopes unveiled the design publicly at Texas Star Party
this year, but only recently
finalized the prototype. They've now entered the production
stage, and we've got an exclusive first look at this revolutionary
telescope. Early this summer, I spent 5 days at a gathering in
Michigan's UP with some good folks - Obsession Telescopes Dave Kriege
among them. He brought the final UC production prototype along
for the ride, and not only
proceeded to put on an excellent dog and pony show, but better
yet - he let me and other amateurs actually observe with the scope.
But before we get there, here are the stats:
OBSESSION TELESCOPES 18" f/4.2 UC (Ultra
correspondance with Dave Kriege
The 18" f/4.2 UC is not a replacement for the Classic Obsession 18
f/4.5. The UC is aimed at users that have very limited hauling or
storage capacity. The UC will fit in any car and thru any doorway. It
will appeal to people that like a minimalist style. The Classic
Obsession 18 is aimed at users that want maximum stability and
ruggedness and do not have transport or clearance issues. It will
appeal to people that like the warmth and beauty of a fine wood
instrument. Optically they are nearly identical except that a Paracorr
is recommended on the UC.
No compromises. The UC uses the same proven design criteria and
materials that made the Classic Obsession so successful.
Eyepiece height at zenith
Set up time including
nylon light shroud
- UC is 71 inches
- Classic is 78 inches
Ease of use (setup, take
- UC is 2 or 3 minutes
- Classic is 4 or 5 minutes
- Add another minute or so for either to place nylon
Ease of Motions (hand
Bearing geometry and
- Same for both. Appleply and Baltic Birch.
- UC components covered with satin black laminate.
- Classic components are stained and have six coat
- Same for both, Ebony star on etch virgin teflon.
Optics (OMI or Galaxy)
- Classic is best with 360 degree upper tube assembly baffle.
- UC 160 degree baffle opposite focuser.
- UC f/4.2 primary mirror requires a Paracorr coma
corrector for optimum views.
- Classic f/4.5 Paracorr optional but not needed.
- Same 3.1 secondary mirror for both.
- Central obstruction and Image contrast the same for
- Same for both. 96% on primary, 98% on secondary.
- UC Six 1 inch diameter. All six interconnected at
- Classic Eight 1.25 inch diameter. All eight separate.
Dimensions of lower unit
- Classic has the edge with 8 pole design and 1.25 inch
- UC has 6 pole design and 1.25 inch diameter poles.
Includes mirror box
nested in rocker
Dimensions of entire
telescope nested for transport
- UC 24 x 24 x 13.5 high (will fit in any trunk or
- Classic 30 x 30 x 30 high
Includes mirror box
nested in rocker with upper tube assembly on top
Custom foam lined travel
- UC 24 x 24 x 19.5 high (will fit in any trunk or
- Classic - Not possible. Upper Tube Assembly cannot be
placed on top.
Upper Tube Assembly weight
(with Feathertouch focuser)
- UC uses a case 26 x 26 x 20 high (see below)
- Classic - No way.
Weight of heaviest
- UC 5 pounds
- Classic 11 pound
(includes 2 inch thick
standard thickness mirror)
Weight at wheelbarrow
- UC is 65 pounds. Includes the virtural mirror box,
mirror, and dust cover
- Classic is 82 pounds Includes mirror box, mirror, and
Weight of complete scope
- UC about 10 pounds
- Classic about 15 pounds
Clearance width required
with wheelbarrow handles attached.
- UC about 90 pounds
- Classic about 140 pounds
(or minimum size of
doorway needed to roll in or out with wheels attached)
Price and options:
- UC 27 inches
- Classic 30 inches
- Same for both.
- The Obsession 18 f/4.2 UC is $6340 and includes the
Feathertouch focuser, Telrad, external light baffle, and counterweight
kit. This is the same price as the Classic Obsession 18 f/4.5 with same
- Optional Paracorr is $295. (Highly recommended at
- Optional ripstop nylon light shroud is $149. (Highly
- Optional Argo Navis DSC with 10K res encoders is $795.
- ServoCAT GoTo drive available late 2007.
- Optional white 26 x 26 x 20 thermo-formed,
high-density polyethylene shipping container foam lined. Case meet the
Air Transport Association's(ATA) Specification 300, Category 1
requirements. is $495.
- (Having scope shipped in this case saves you about
$200 in packing costs).
A thank you to
Obsession Telescopes for allowing CN to reprint this correspondance in
We were impressed. But more on that later.
As I've mentioned, there are always design trade-off's involved in an
instrument. Previous ultralight designs have sacrificed
weight for stability - resulting in both flexture and, well, a
skittishness in the motions. Lets face it, current
non-ultralight scopes have
spent 10-15 years evolving and are quite
good. To take it to the next level as per portability, it seems logical
have to give up something.
The UC gives up very little - except size.
Collapsed, the scope is absurdly small. The rocker box isn't
more than a couple of inches off the ground (if that), and there really
isn't a mirror box. (Kriege referrers to it as a virtual
mirror box.) The bearings are reinforced with steel plate, and
fold into two pieces for the ultimate in portability. All exposed
steel is stainless. The primary
support system utilizes a Kevlar sling, and an 18
point cell that has a small cooling fan attached. The mirrors are
f4.2 and will be supplied by long time associates Galaxy and
OMI. They are (what is termed as today) standard thickness mirrrors.
As you can see, the Obsession Ultra Compact is a six pole, single ring
upper truss design. The six poles are fastened together at the
ends and accordion to make life easier during transport - no
loose poles floating around. They also do a darn good job
of eliminating flexture. This scope stays in collimation
parked or slewing.
On the single ring upper truss assembly (UTR) you'll spot a couple of
interesting things. First off, the FeatherTouch focuser is
standard, and it's mounted on top of the UTR. The foam covered
handle is an excellent touch and is in the perfect location for most
observers. The Telrad is mounted on a post that also projects
the UTR and in an interesting design move, the post is hollow and is
used to hold the
counterweights - three of which are supplied with the system. This
allows the user to go from lightweight mono eyepieces to heavy
with a minimum of balance issues.
Those of you wishing to computerize the setup need not fear about
clearance - a recess
is provided in the ground board for the AZ encoder and provisions have
been made for a virtual encoder mount for the ALT. The computer
mounted to a clip that attaches to the truss poles, placing it in a
very natural position.
One of the major concerns dealt with the initial apparent lack of a
shroud. Dave Kriege is well aware that most of us consider a
shroud necessary (for a
number of reasons), and has devised a system that keeps the shroud
tight over the scope and out of the light path. The shroud
will be an option for the production units. Because the
focuser is mounted above the single ring UTA, a light shield is
as standard equipment.
The secondary sports tool less adjustments, and features an
Astrosystems dew guard kit. (No, the high tech
secondary cover shown in the images above is not included. You'll
have to use your own sock.) The shroud ends a
couple of inches above the primary, but thermal inertia should work
fairly well to keep dew from forming on the primary until way into
the early hours - at which point you'll most likely be asleep anyway.
As you can see, the mirror is more exposed to incidental dust and dirt
than in a traditional design, but that's one
of the few trade-off's for the ultra light weight and portability of
the Obsession UC.
Wheel barrel handles are available for the observer who wants to keep
the scope fully assembled and roll it out to observe. The scope
can be locked into position using a Velcro strip. Additionally,
the front and back edges of
the rocker box are padded to help prevent you from dinging up
the corners in storage or transport.
While it's not a done deal, Obsession is considering offering the
transport case shown in the
photos for resale. While increasing the room the scope
takes up, it allows for "no worry packing" - a boon for those of us who
vehicles that are already crammed to the gills.
Initial setup and collimation took a matter of mere minutes (probably
less time than it took you to look at the pictures). The
collimation adjustments for the secondary are
easily reached from the eyepiece, making that last bit of tweaking a
Observing with the scope was a blast. The 18" UC is - hands down
- the best star party scope I've had opportunity to
The shroud and shield worked well - contrast was
very good, and there were absolutely no dew issues. Another fear;
unwary observers would kick sand and dirt on the mirror proved
to be pretty much a non-issue. But as the optics arrived a little
dirty (this is the 5th prototype this optic set has seen light in) Dave
demonstrated how the open design lends itself to cleaning
At f4.2 you really do yourself a disservice if you're not using a
paracorr but with it, images are spectacular. The 31mm Nagler in
makes an excellent low power eyepiece for picking off targets. It
provided a true field of just over a degree and magnification around
We spent the first part of the evening with the telescope, and I had
ample opportunity to put it through it's paces. The scope was at a
decent height - I'm 6 foot 2 inches, and most of my observing was done
with my feet on the ground. For targets within 10-15 deg of zenith
however, a small step was necessary. In use, the UC
didn't feel like an ultralight. For one reason or another, the
ultralights I've used
have been a little skittish. Not much of that here. And you're probably
wondering about the patented "Obsession" motions - while
the motions weren't quite as smooth as the classic
Obsession, they were as smooth as or smoother than most of the other
dobsonians on the market. I expect they can be
tweaked a bit further, but as it stood, they were most certainly good
enough. There was a slight bump evident in the alt motion
at one vertical position, but Dave Kriege tells me this will be pretty
eliminated from the production scopes. The only other
differences will lie in an improved fit and finish.
And speaking of production: the 18" Ultra Compact is expected sometime
this fall. Pricing is (tentatively) set around that of the Classic
with the FeatherTouch upgrade.
All in all I was very pleased with the performance and portability of
the telescope - so much so that I'm giving serious consideration to one
planned 15" versions for my own personal ultimate travel / star party
scope. The 18" was
lightweight, quick to setup and easy to use with very few drawbacks as
compared to the classic design. Everything that a telescope is
supposed to do, it did. And quite well at that.
Twenty years ago, Dave Kriege helped revolutionize the dobsonian
He's doing it all over again.