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CN Report: The DiscMounts DM-4
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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,
doing the funky chicken when dancing around the mount trying to look
the eyepiece. They’re well, Zen.
There are however, some disadvantages to
mounts – namely that they are extremely sensitive changes in balance,
be a pain at high powers.
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:
(perfection isn’t cheap) and weight (stability comes at a price).
Tom’s had multiple requests from
(both current and potential) to address this in the form of a
less expensive mount that folks can travel with and thus was born the
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
materials required. The DM-4 also
differs from the DM-6 in a couple of other minor ways;
At this point, I’ve used a DM-4 for several months, with a
variety of telescopes; Coronado SM60, the NP101, TV102, a StellarVue
and several other telescopes.
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
shorter tripod. With the taller tripod; I am now able to use my
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
worked very well for a buddies Solarmax 60. With
a beefy camera tripod, and a small, short,
kept to moderate powers – it may be just the ticket for someone looking
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
encoders (look for a review of the new Sky Commander down the road),
a tilted plate above the head itself. This
arrangement (like the DM-6) allows Tom to hide the
entirely within the DM-4 head and eliminates any problems with cord
wrap. While DiscMounts sells the Sky
4000 tic encoders with its mounts, the system is compatible with nearly
system on the market. Although I rarely
use DSC’s on small telescopes anymore (I seem to go in phases) the
mount them is something that many observers will appreciate –
observing deep within the light dome of an urban area, or observers
looking to actually
observe instead of hunt for their objects.
now includes 18” of
cable (stored inside the DM-4 head) to mount the DSC where ever you
– if that’s not enough, you can visit any Radio Shack to obtain the
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
choose. Many users request the mount
be set up for the Argo Navis. Because of
its programming the Argo needs a fixed reference point to mark its
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.
So how does this mount
compare to say – a
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
fairness is only if you’re moving to extremely heavy eyepieces or
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
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
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
for a sleep deprived brain to remember. Putting
the DM-4 to bed one night in the process of separating the scope and
unscrewed the lock knob too far at which point the knob fell on the OTA
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
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
When all is said and done the DM-4’s greatest competition
probably the DM-6. Frankly, Tom’s done
an excellent job of scaling down the DM-6, but with the 6’s capability
handle a wider range of weight changes, one should think long and hard
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
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
For pricing and options contact:
You can find the DM-6