T-Rex Heavy Duty Alt / Az Mount
Submitted: Friday, 14th January 2011 by Peter J Hexter
The use of Alt / Az mounts seems to have undergone a bit of a resurgence in the last few years. Most visual observers find the ease of set-up and use a pleasant change from the effort of a Go-To GEM. Two minutes and you’re observing with no worries about alignment, power supplies or tracking accuracy. Newtonian owners, especially, like them because they keep the eyepiece in an easy to reach position.
However, one of the drawbacks to these mounts is that, typically, they are designed for smaller telescopes and have a limited weight capacity.
There are exceptions of course: the Discmounts DM6, the Half-Hitch and the Stellarvue M7, plus one or two others. All of which are excellent mounts in their own right, but all, to my mind, fall slightly short of:
A Brief History
The T-Rex mount is the brainchild of Barry Gooley at Kokusai Kohki in Japan. It was designed following a lengthy survey of users observing habits and preferences. It is obvious that a lot of thought has gone into its execution and it was specifically designed to take a good deal of weight while retaining a smooth and accurate action.
It does not disappoint. In fact it excels. Particularly with large, bulky ‘scopes.
Arrival and Assembly
The mount and tripod arrived in Australia from Japan about 3 days after I paid for my order, and after being held for ransom by customs, was delivered to my house in rural Victoria. On un-boxing it was readily apparent that this is no slap-dash effort.
The T-Rex is machined out of aluminium stock with brass gears and drives. It is robust and solid with a pleasantly hefty feel. It weighs about 7kg excluding tripod and OTA. Much lighter than an equivalent capacity GEM and a bit lighter than a DM6 when fully assembled.
All of the technical data you’d want to read is on the English Kokusai Kohki webpage, so I won’t reiterate it here.
Everything you need to assemble the mount is in the boxes: wrenches, bolts, cords, etc. It took me about 20 minutes, including double-checks and ‘lost’ items. Assembly instructions are clear and easy to follow.
The head mounts to the tripod in the same way as Synta equatorial mounts: via a threaded rod through the hole in the base and spreader. The part NOT to be used with the T-Rex is the positioning pinion for an EQ6 head. A large (M10) Allen bolt pre-attached to the tripod base-plate does the job here.
Aesthetics & Specs
Fit and finish is superb, with deep, quality powder-coating, (first-run units were anodized), beautifully machined parts and big, fat stainless steel Allen bolts. It looks the business. I’ve tipped it on the ground a couple of times and the surface has held up admirably.
I ordered mine with the tried & true Synta HEQ6 tripod which provides an extremely solid base and helps damp vibration very well. About 0.5 to 1.5 seconds depending on the tube.
The T-Rex is also available with the Vixen HAL 130 tripod or as the mount head only.
Personally, I feel the HAL130 would not really be up to the job of supporting both the head and a heavy OTA but as they say, YMMV. An adapter plate is available if you want to mount the head on one of the larger photographic tripods. Personally I wouldn’t use anything less than a Berlebach or equivalent.
The mount is available with a choice of saddle plates and I chose the included Vixen type which is big and solid with reassuringly large grub-screws. The mount itself is tapped with 4 M8 holes on 35mm centres meaning that it accepts pretty much all Takahashi and Losmandy saddles.
The T-Rex avoids the use of counterweights by off-setting the main control mechanisms and centering the tube cradle over the middle of the mount. This appears to be feature shared only with the Half-Hitch in this weight category. I find this a real boon as I hate fumbling with bars and counter-weights and almost always run into them in the dark.
The mount is equipped with 4096 step encoders for use with KK’s own Super Navigator, or indeed any DSCs (Digital Setting Circles) that are compatible. The mount has 2 white register marks, one at 0 degrees and one at 90 degrees, to allow fine initialisation .
It is actually quite difficult to be very technical here because, quite simply, the T-Rex does what it says on the tin. Though if anything, it’s a little bit better than you expect.
Mounting an OTA is simplicity itself and, like any mount, a bit of care is needed in initial balance of the tube. Be sure to tighten the Alt/Az tension levers to full though, otherwise you wind up chasing the mount around and around until it finally occurs to you to do so!
Once set-up is complete you’re ready to observe. Back the tension bolts off by 1/8 to 1/3, depending on how quick you want the movement to be, and away you go. Using both my Newt and my refractor, I found a quarter-turn ideal for both slewing and close tracking.
What can I say about it?
It goes up. It goes down. It goes around and around. Pretty much all you ever need from an Alt / Az mount really.
But it does so with complete smoothness and surety. There is no backlash. The slow motion controls are beautifully fluid and accurate and the solidly made handles ensure that minimum vibration is transferred to the mount. This solidity is particularly welcome in my area, which is subject to gusting winds for much of the year.
KK offer only a ‘ballpark’ maximum weight limit (16kg) for the T-Rex, but to date mine has taken a TOA 130 with 4” focuser - easily 20kg, a 10” Meade LX200ACF, my TSA 120 and an 8” GSO Newtonian without a hint of stress. In every case, the mount retained its composure and ease of use. Fortunately it handles lighter scopes like the ED80 with just as much aplomb.
Even swapping-in the massive 31 Nagler from a 7.5 Tak LE in the 130 did not upset its balance. Nor did adding the ED80 to the 8” Newt.
All accomplished without a single counterweight. Splendid!
For more extensive (and better) images of the OTAs the mount will hold, please follow this link and scout around.
A few days after arrival, using a 5mm Tak LE in the TSA and a 12mm in the Meade on Luna, we were able to keep Eudoxus (one of the smaller craters) and its companions in plain view with no visible vibration wile tracking. In fact Luna was such a pleasant target with the TSA/T-Rex combo that I spent an all-time personal best of 3.5 hours observing.
During a break in the clouds some days later, I sought out Jupiter and tracked it at high power (270x) with both the 8” Newt and the TSA120. Once more – no visible vibration.
Even the TOA 130, a long, heavy tube, could not ruffle the mount’s feathers. I spent nearly two hours observing Centaurus , Carinae and Orion in fairly stiff winds (15kph +) with only minimal disturbance of the OTA. A strong gust would cause a noticeable flutter, but not so much as to completely ruin the view. Impressive!
If you are primarily or even partially, a Lunar or Planetary observer, this mount will truly shine for you. I can’t think of single mount this side of an AP900 that will hold a scope as steadily. As I mentioned, the slow motion controls are very smooth and allow tracking at high power with fine accuracy. The turn handles could be longer as a long refractor will extend the focuser end a fair way ‘down’ but you can also use flexi-cables if so inclined.
With the TSA 120 and a Meade SCT, I can reach full zenith without hitting the tripod legs. The TOA130 required a bit more care but would still clear them. The Newt was different matter. With an ED80 piggybacking, a Binoviewer and two 6mm Ethos’s, we had to mount the tube fairly low and therefore couldn’t quite get to zenith. I believe extension piers are now available though, so that should take care of that.
The only readily to-hand competition is the DM6. Just up the road, is a man who has one.
While the DM6 is a solid and capable mount it lacks a few “extras”.
The addition of slow-mo controls with handles and lack of the need for extension bars or counterweights make T-Rex an easy choice for me. In fact, they are the main reasons I chose it in the first place. The DM6 remains a fine unit, and was perhaps, the ne plus ultra of Alt / Az mounts. Until this mount came along.
Summary. Good and ..... ?
Although this review is obviously pro- T-Rex, it is so for a reason. Finding a bit of equipment that actually meets your expectations, let alone exceeds them is pretty rare these days. I’m very fussy. I can’t stand second rate gear at first rate prices. So when this mount turned out to be just that little bit more, I was very pleased.
Realistically the only downside to this mount is that it’s fairly expensive. In fact it was only a matter of $100 or so between it and a DM6 flown in (business class, by the price) from the US. Prices vary with exchange rates, and mine cost the thick end of AU$2000. But, the Australian dollar is currently at a good rate and prices should be a bit lower.
On the practical side it would also be a HUGE plus to be able to motorise the mount. It’s just crying out for them!
Perhaps in the future.......?
All things considered though, this mount is “sensibly perfect” if you are looking for a heavy duty Alt/Az mount that can handle all but the largest commercially available ‘scopes, then look no further than the T-Rex.
T-Rex’s are now available in Australia through the fine folk at AEC (Astronomy-Electronics-Centre). I believe they are trying to keep prices down buy sourcing the tripods locally. Good show!
Many thanks to Tamiji Homma for the links to his pages. He is one of California’s premier amateur astronomers and tech gurus and is a regular contributor on cloudynights.com