Cn Report:
DiscMounts DM-4
Zen - Now in a smaller package!
Tom Trusock – 12/05
Tom
Peters has done it again.
Tom owns and operates DiscMounts
– if you aren’t familiar
with them, then you’re probably not aware of one of the best alt/az
mounts on
the market. Two years ago, Tom introduced his first product - the DM-6,
a
revolutionary high quality alt/az mount for the discriminating visual
observer.
Make no mistake; I’m a big fan of alt/az mounts. For 90% of my observing, they are far more
convenient than GEM’s – no messing with polar alignments,
counterweights or
doing the funky chicken when dancing around the mount trying to look
through
the eyepiece. They’re well, Zen.
There are however, some disadvantages to
traditional alt/az
mounts – namely that they are extremely sensitive changes in balance,
and can
be a pain at high powers.
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What I liked |
What I disliked |
- Little brother to the DM-6
- More portable
- Sits much better on a large Bogen / Manfrotto
- Less expensive than the DM-6
- Tray now available
- Best mount in it’s class
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- Still a bit heavy for travel
- Balance range not as large as DM-6
- Tom Peters still won’t give them out for
free
:-)
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DiscMounts design allows you to eliminate rebalancing or
tension adjustments when moving between heavy and light eyepieces – and
not at
the sacrifice of ease of motion. Because of the large disc assembly used to
provide friction for the bearings, locking the axis becomes unnecessary
when
changing eyepieces - and the scope will stay on target! Smooth motions
at high
powers are the norm, with the ability to go from lightweight to heavy
eyepieces
without having to rebalance the telescope.
Everything about the
DM-6 is first class, without a doubt it’s one of the best mounts on the
market. In form and function, it’s tops. Tom’s attention to detail is extraordinary. IN
fact, there were only two things that a consumer might find fault with:
price
(perfection isn’t cheap) and weight (stability comes at a price).
Tom’s had multiple requests from
his customers
(both current and potential) to address this in the form of a
lighter,
less expensive mount that folks can travel with and thus was born the
DM-4.
My first impressions were that the DM-4 was
a DM-6 after
Atkins. The bearings are 4” instead of
6”, allowing Tom to reduce the overall size of the head and reducing
weight and
materials required. The DM-4 also
differs from the DM-6 in a couple of other minor ways;
- The sides of the DM-4 are attached by hex head screws –
even the side plate. On the DM-6 this just
slid in and out.
- The tension adjustment wrench does not store inside the
head like it does with the DM-6.
- Because of its lighter weight, the DM-4 is
better suited to a heavy duty camera tripod like the Bogen / Manfrotto
425/3036, which makes it a better option for travel (with a few caveats
that I’ll discuss later).
- Because of its smaller bearings, the DM-4 does not deal
with the same range of weight changes as gracefully as the DM-6 does.
- Since it’s a smaller mount than the DM-6, the load bearing
capacity is naturally a bit lower
 (15 - very conservative lbs vs 40 lbs).
At this point, I’ve used a DM-4 for several months, with a
variety of telescopes; Coronado SM60, the NP101, TV102, a StellarVue
NightHawk,
and several other telescopes.
Performance?
The DM-4 - like the DM-6 – is everything Tom bills it.
On the default tripod, the DM-4 handled everything
I could throw at it with aplomb. My
worst case scope was the TV102 – due in part to its weight and long
moment
arm. The DM-4 held the TV102 very
well. Motions were smooth at 300x, and
damping time was a mere 2-3 seconds (max). IMO,
the damping time was only that long
because of the single clamshell ring that TV uses.
Dampening times were in fact, even shorter
with the FS102. I
found the scope to balance well with
eyepieces ranging from my 17mm t4 Nagler (25.6 oz) on the heavy side to
my 3-6 Nagler
Zoom (5.6 oz) on the light. If I wished
to use the mount/telescope with a binoviewer, it was a small matter to
slide
the OTA forward in the clamshell ring and rebalance.
If you change OTA’s or accessories often, Tom
recommends using a long balance plate, and making note of where the
balance
position may be with different accessories. Then
place a small piece of tape on the backside of the
plate and label
it for that particular scope or accessory.
DiscMounts now also offers a tray for their tripod – taking
up the entire area inside the bars used to lock the legs in place, it’s
made of
a very thick Delrin like material, easy to install, very large and
quite stable
(and highly recommended).
Tom offers two different heights for the tripod, and I was
shipped the taller version along with the mount itself.
Of the two heights, this is the one I prefer
for stargazing. I’m a big guy 6’ 2”, and
had to plant my rear on the ground when gazing at or near zenith with
the
shorter tripod. With the taller tripod; I am now able to use my
observing chair
at all times – thus I find it far more comfortable.
Make your choice accordingly.
The DM4 is probably one of the most stable setup’s I’ve ever
used. The balance, damping time and
overall usability of the mount (on Peters tripod) simply improved as I
moved to
shorter (and smaller) OTA’s.
However, the story wasn’t quite as rosy when I mounted the
DM-4 on my Bogen 3036. While performance
was fine for smaller scopes, it suffered noticeably with the larger
ones. Because of the longer length and
single clamshell
ring, the telescope affected the worst by the tripod switch was my
TV102. Dampening times increased to 5-7
seconds at
high power. Vibration suppression pads
cut this in half, but its just one more thing to carry.
I’ve wondered why Tom has never recommended
a collapsible mount for use with the DiscMounts – now it’s clear. The vibrations I experienced were in no way
the fault of the head, it was clearly the tripod. While this setup
would work
in a pinch, I probably wouldn’t recommend mounting anything heavier
than 10-12
lbs on the DM-4 if it’s on anything other than the DiscMounts tripod.
One other point- the DM-4 Manfrotto / Bogen 475 / 3036
combo
worked very well for a buddies Solarmax 60. With
a beefy camera tripod, and a small, short,
lightweight telescope,
kept to moderate powers – it may be just the ticket for someone looking
for a
portable solution that has exceptionally smooth motions at high powers.
Got Computerized
Pointing?
The DM-4 shipped with a new model Sky Commander and 4000
tic
encoders (look for a review of the new Sky Commander down the road),
mounted on
a tilted plate above the head itself. This
arrangement (like the DM-6) allows Tom to hide the
cords almost
entirely within the DM-4 head and eliminates any problems with cord
wrap. While DiscMounts sells the Sky
Commander and
4000 tic encoders with its mounts, the system is compatible with nearly
any DSC
system on the market. Although I rarely
use DSC’s on small telescopes anymore (I seem to go in phases) the
ability to
mount them is something that many observers will appreciate –
especially ones
observing deep within the light dome of an urban area, or observers
looking to actually
observe instead of hunt for their objects.
Tom
now includes 18” of
cable (stored inside the DM-4 head) to mount the DSC where ever you
would like
– if that’s not enough, you can visit any Radio Shack to obtain the
correct
connectors and extensions. This means
that you can use Tom’s tilted top mount (show in the article), mount
the DSC on
the front of the DM-4 itself, a leg, the tripod or basically anywhere
you
choose. Many users request the mount
to
be set up for the Argo Navis. Because of
its programming the Argo needs a fixed reference point to mark its
position in
relation to the mount in addition to a two star alignment.
Thus, Argo setup and reference marks are
available by request for an additional charge.
The accuracy of the DSC pointing depends
heavily on the
construction of the mount. In short, it
requires that the mounts axis be perfectly perpendicular to each other
–
orthogonal – for best results. To make a long story short, the DM-4 is
orthogonal. Period. DSC
pointing accuracy was everything one
could want. It easily allowed me to
center objects at high power.
Image
courtesy DiscMounts
So how does this mount
compare to say – a Gibraltar? First, the
ability to not
have to rebalance or tighten your tension is - well – pretty dang nice. It’s hard to describe until you get used to
it. But once you do, you come to
appreciate it. Another area in which the
DM-4 surpasses the Gibraltar is when you
increase the
magnification above 150x or so for detailed lunar and planetary
analysis. The DM-4 is far more stable, and
the motions
are much smoother easier. High power
hand tracking is very doable with the DM-4. In short, while detailed
investigation of the moon and planets can be a chore with the Gibraltar,
the DM-4 invites it – especially when it comes to using smaller AFOV
eyepieces. Finally, you’re limited by the
OTA size – so
the DM-4 can accept a wider range of OTA’s – like an 8” SCT.
Perfection?
Nearly.
Ironically, I’d almost like to see an altitude lock or
tensioning screw that’s easily accessible. The
DM-4 does not handle the extreme weight differences
the DM-6 does,
and a lock would come in handy while you rebalance the telescope (which
in all
fairness is only if you’re moving to extremely heavy eyepieces or
accessories
like a binoviewer). You can, of course,
tighten down the Alt axis to compensate, but then motions tend to
become a bit
stiffer than I prefer. I should note
that shorter scopes tend to have less of a problem as their moment arms
aren’t
as long.
Another “flaw” isn’t really in the mount; it’s in the fact
that it uses the Losmandy 4” saddle plate. While
this is one of the most common arrangements on the
market today,
it does have one drawback. The lock knob
isn’t captive. Why should this
matter? Well, let’s step back a moment
and think about this – Go back to the
design of the G11 saddle - it’s not a tip in plate – something that’s
very hard
for a sleep deprived brain to remember. Putting
the DM-4 to bed one night in the process of separating the scope and
tripod, I
unscrewed the lock knob too far at which point the knob fell on the OTA
and
took a small chip out of the paint. Soon
thereafter I had a talk with Tom and he assured me he’s been looking at
implementing
a solution for a while.
The final drawback is a fiscal one. While
the DM-4 is certainly less expensive than
the DM-6 (and fairly comparable to a completely decked out Gibraltar),
it’s still not an inexpensive mount anymore than a fully loaded H2
would be an
inexpensive car. If you want quality,
(and the DiscMounts ARE quality, on that rest assured) you are going to
have to
pay for it – that’s one miracle even Tom Peters can’t pull off.
Final Words
When all is said and done the DM-4’s greatest competition
is
probably the DM-6. Frankly, Tom’s done
an excellent job of scaling down the DM-6, but with the 6’s capability
to
handle a wider range of weight changes, one should think long and hard
about
which to purchase – the 4 or the 6.
DiscMounts have again shown they make the Cadillac ALT/AZ –
the only question is, do you want a midsize or full size?
I’d talk it over with Mr. Peters, but my
recommendation would be the DM-4 would be perfect for a 4-5 inch or
smaller apo,
or an 8+” CAT. Anything larger or longer,
I’d want the DM6.
Overall, DiscMounts has given us another top notch alt/az
mount. If you’re a visual observer
looking for a top-of-the-line luxury alt/az mount – DiscMounts sits
atop the
heap.
For pricing and
options contact:
DiscMounts
http://www.DiscMounts.com/
tom@DiscMounts.com
954-475-8574
You can find the DM-6
Review here
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DM-4
Specifications |
Azimuth axis
(Tripod) mounting hole:
3/8"-16
centered on 4" disc
Altitude axis (Saddle)
mounting holes:
DM-4: 1/4 " - 20 spaced 3" apart (compatible* with the Losmandy G-8 and
G-8D saddle plate system) centered on 4 " disc
*Please note, due to the diameter of the DiscMounts' disc DiscMounts’
modifies the G-8 saddle plate
Material:
All aluminum is 6061-T6 hard coat anodized and machined to
close tolerance from sold blocks. All hardware, shafts, and ball
bearings are made from stainless steel Weight no accessories: DM-4:
5.2lbs
Dimensions:
DM-4 Head only: 5 3/4" long, 4" wide, 5" high Height to
center of Altitude disc: 2 1/2" Head Load weight: DM-4: 15 lbs (load
weight varies with diameter and length of tube)
Eyepiece/Camera
deferential load weight to maintain balance (at end of
focuser) - DM-4:
0 to 1.5 lbs. typical
Please note this can change up or down depending on the telescope and
the highest magnification required.
Ash Tripod Specifications:
Ash Wood Tripod: Natural
oil, Red Mahogany stain with oil, or Walnut stain with oil
Top plate DM-4:
4" diameter with 3/8"-16 mounting pin. All
aluminum is
6061T6 hard coat anodized, and machined to close tolerance from sold
blocks. All hardware is made from stainless steel
Legs:
3" wide, 1 1/4 thick, solid Ash non-adjustable
Maximum load weight
including mount head: 15 lbs. (with spreader braces
installed)
Leg spread circle stand
Ash Wood Tripod: approximately 37" to 39"
adjustable
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