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Vixen Custom D Alt-Az Mount


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Figure 1 - Vixen Custom D Mount & Tripod

Background

For some time I had been looking for a well designed alt-az mount. It had to be light, compact when collapsed, and come with those (for me) all important fine-motion controls. Oh, needless to say, it had to be steady as a rock when carrying my beautiful, new Borg 100ED refractor. (See David A. Novoselsky’s excellent review of the Borg 100ED).

Yes, I wanted a mount that I could simply forget was ‘there’ during viewing. Just myself, clear night skies, no streetlights, two precise and fluid fine-motion controls, a comfortable chair, and the heavens above…

That shouldn’t have been too difficult a task, one would have thought, but an exploration of various internet sites, especially these hallowed halls, revealed that choices are few. It was my requirement for fine-motion controls, you see; all the usual suspects failed to meet that particular requirement. Just as I was beginning to relent, and buy a Tele Vue Telepod, thereby joining the massed ranks of ‘nudge-nudge-whoops-too-far’ astronomers out there, I read yet another David A. Novoselsky review, the one of the Vixen Custom D versus TV Gibraltar. Now, after my wonderful Borg experience, I had come to respect the learned Mr Novoselsky, so my choice was made: the Custom D got the job.

Then I just had to find one here in Switzerland.

Now, astronomical equipment is not exactly thick on the ground, here, but it just so happens that the main Swiss Vixen importer is based here in Zürich. I made a quick phone call, and they had a few in stock for about CHF 900 ($600). A quick trip there, and they let me have it for ‘only’ CHF 800 ($533).

Description

The Custom D is a alt-azimuth mount with fine-motion controls. Maximum payload is hard to determine, but it seems that owner satisfaction is great up to a maximum of about 8kg (18lb).

It has a counterweight shaft which can be used optionally with heavier telescope OTAs. It comes with the usual Vixen AL90 tripod, which has extendable legs and a really super leg spreader. An excellent accessory tray is available that sits on that spreader, (and I really should buy one, quite soon). For some inexplicable reason, it doesn’t come with a travel bag. Humph!

The azimuth clutch system works by loosening or tightening the large coupling between the mount and the tripod; thus, both mount and tripod should be seen as being a single unit. It can be used on various Vixen tripods, but there’s no obvious way you can use it on other tripod designs. The altitude axis is not clutched, and is simply tensioned ( a one time job) by way of a large nut.

Both fine-motion axes work by way of a captured thread and tangent arm (see Figure 2). This allows a total fine-motion range of about 30°, on either axis.


Figure 2 - Mounting plate recess & altitude fine-motion control

The mount/tripod weighs 4.3kg (9.5lb) and the optional-use counterweight shaft weighs a further 3.4kg (7.5lb). Assembled, the overall height range of the mounting plate recess can be set from 84cm (33”) to 135cm (53”), simply by adjusting the length of the tripod legs. Fully collapsed, the mount/tripod combination measures 90cm (35.5”).

How it fared

It works fine! But not without a few caveats, so please read on…

Collapsed, the mount/tripod slid easily into the smallish boot (trunk, to non-Brits) of my car, alongside the blue Borg OTA bag, plus my ‘eyepiece-junky’ soft-case. Whilst I still wished that the tripod could be collapsed still further, and that it had come with a proper soft-case, I had to admit that already it had passed the portability test with flying colours.

Setup, on the wonderful terrasse of my wife’s family’s châlet in the Swiss Alps, was fast and easy: I simply turned the mount/tripod upside down, lengthened the tripod legs about halfway, making sure each leg was extended about equally, and properly clamped in place. Then, I righted the mount/tripod, and opened the legs; (unlike some horrible designs that I’m trying hard to forget), the leg spreader simply opens up like a flower. Then I attached the Borg OTA by carefully placing the mounting plate into the standardised Vixen mount recess, (see Figure 2), and tightening the security knob. As always, I tested the security of the OTA by lifting up the OTA, mount and tripod altogether. Then, I made sure that the fine-motion controls were centred, so that they had around 15° travel either way.

At this point, owners of heavier OTAs will want to attach the counterweight shaft. As my Borg 100ED weighs about 4.5kg (9.9lb), (even with the superb 7x50 finder, 2” diagonal, and my heaviest 2” eyepiece), I dispensed with this.

In action, later that evening, I used a globular cluster viewing programme in order to thoroughly test the Custom D. Globulars are small and require at least 100x magnification, and usually can take much more; thus, they take some fine adjustments to locate, and then plenty of manual tracking to keep them in the field of view. So, I used the finder to locate M13 (of course, smirk) and then my 15mm eyepiece (43x) to make sure it was centred in the field of view. It was. Then I swapped the 15mm for my beloved 3-6mm Nagler Zoom. At the 5mm setting (128x) M13 resolved about as well as it can in any 100mm (4”) refractor; I was engrossed, of course.

It was at this point that I realized that my coarse movements of the Custom D in both altitude and azimuth had been performed without any conscience thought on my part. I had simply pushed the OTA until it pointed towards those two stars in Hercules between which M13 resides. Fine-motion had been less unthinking, as I was making all the usual mistakes, i.e. when attempting to adjust a bit to the left, I’d managed to slew upwards, instead. Realising my mistake, and switching to the other fine-motion control, I then slewed right instead. Ah well, I really couldn’t blame the mount for that. As time has passed, and I’ve become more accustomed to the Custom D, these sort of transposition mistakes have almost disappeared.

Yes, the mount has begun to ‘disappear’, just as I had wished at the beginning.

Furthermore, when using either fine-motion controls at 128x, the image shake settled down in a lot less than a second. Impressive. An sharp, accidental kick of the tripod showed that the image settled down in about a second. During later viewings, I’ve found that even a 213x, the image shake settles down very quickly, somewhere between one and two seconds. Leg extension is definitely a factor, and when the legs are fully extended, the settle-down time is closer to two seconds at 213x.

Devil in the detail

Switching to M3, I found my first major issue. It just so happened that my previous target, M13, had been at the perfect elevation for comfortable viewing while seated. Switching to M3 (at a lower elevation) meant that the back of my OTA had naturally pivoted up quite a lot; thus I was now stood up, and peering down my 2” diagonal with the small of my back bent: Shock! Horror! I was now uncomfortable! Now, you refractor veterans out there are wondering at my naivety, but I really hadn’t experienced this before, as my previous telescope, an ETX-105, didn’t suffer anywhere near so much height variation, unless viewing the zenith.

Seeking comfort, I went through a routine worthy of Laurel and Hardy, while I adjusted each tripod leg downwards, one at a time, ‘in flight’, as it were. My wife viewed the entertainment, and her remarks gravitated from strong concern for the wellbeing of my expensive Borg 100ED (paid for out of our savings, you understand), towards outright mirth. Yes, I looked an idiot, but my Borg survived that experience. Somehow. Only, of course, I hadn’t quite shortened the tripod legs quite enough. Just as I was about to repeat the exercise, my wife stepped in, and (amidst a fit of giggles) insisted that I ‘do it properly from now on’; She meant that I should dismount the OTA, then turn the mount/tripod upside down, and adjust the legs that way. Hmm, ok. And Darling, if you’re reading this, I have continued to be a good boy ever since.

Now, comfortable again, I discovered another problem that I hadn’t noticed at first: there’s some ‘play’ in the altitude axis, which means that the coarse aiming in that direction is not quite a satisfying as it should be. The ‘play’ turned out to be inherent in the design of the altitude fine-motion control. While not a major problem, I considered that it was still less than ideal, and should be investigated and corrected by the Vixen designers.

That was enough globular viewing for one night; I decided that a lengthy scan along the Milky Way would be an ideal way to end the evening, especially as it went right across the zenith. (OTA off, legs lengthened, OTA on again). Switch to my big, heavy 30mm widefield 2” eyepiece, And… wow! “It’s full of stars…” as they say. Only, I then discovered some further problems with my Custom D:

Firstly, I needed to readjust the altitude tensioner, as the OTA plus 2” eyepiece (even when properly balanced) was tipping the mount backwards ever so sloooooowly. The altitude axis of the mount itself is offset from the centre of gravity, so no amount of telescope rebalancing was going to solve this. The following day, I found a spanner, adjusted that tensioner nut, and the problem has gone away for ever. Strange that Vixen don’t have a better tensioning method for the altitude axis. Perhaps the ‘one-time adjust’ nature of this tensioner is the reason?

Secondly, as the tensioner problem had yet to be resolved, I was simply chasing the field of view upwards by matching this slippage with the altitude fine-motion control. That’s when I found that what I had thought would be a generous 30° range of adjustment in each fine-motion axis, can quickly run out. Then, one must unwind the fine-control to about the centre of its adjustment range, and then coarse move the OTA. Bah! This is not ideal, this will not go away, and I must learn to live with it.

Thirdly, I found a blind spot near the zenith where the OTA itself would meet a tripod leg. This is again easily solved by rotating the mount/tripod so that the OTA slips between two legs at the zenith. I can live with that, and am always careful to ensure that the tripod legs are positioned ‘just so’ right at the start of the viewing session.

Lastly, and my hands are shaking as I type this, I nearly had one of those accidents that amateur astronomers have nightmares about: reaching blindly for the azimuth fine-motion control, I inadvertently grasped the safety knob that clasps the OTA mounting plate firmly in the mount recess. Yes, I then turned it a few times, and the OTA (released from captivity) started to slide backwards into my lap. I caught it, slid it back, tightened the security knob again. Then I went inside the châlet to have a coffee, and to calm my nerves. Why did it happen? Because the design of the security knob is identical to the design of the knobs on each of the fine-motion controls. Check out Figure 2 again, if you don’t believe me. Obviously, since that slip, I’ve been very careful indeed. It hasn’t happened again, and it won’t.

So, with my first evening with the Custom D over, it was time to pack up. All in all, a successful night, both as a viewing session, and also as an equipment test. Now, why on earth don’t Vixen supply the Custom D with a bag...

Summary

In summary, I since that first evening, I've become rather attached to my Vixen Custom D.

It’s steady as the proverbial rock, is simple to setup and use, and has those fine-motion controls that I hold so dear to my heart. It’s light and compact, (especially without the counterweight shaft), and somehow feels like a properly designed ‘product’. At any price, this seems to be the best fine-control alt-az available. I’m keeping it, and I’ll simply learn to live with its few detriments.

What would I improve if I were a designer at Vixen?

Well, those Vixen tripods really need a height adjustable centre column, rather like Bogen/Manfrotto/Gitzo include on many of their tripods. Many a refractor freak would then be able to cancel their regular appointments with their osteopaths. Oh, and perhaps those tripod legs could then be redesigned to collapse still further? 90cm (35.5") isn't too bad, but imagine how much more portable it would be if it could collapse to around 60cm (24"). Well, one can dream.

Next, that restricted 30° range of the fine-motion controls should be replaced with a 360° design, just as the Good Lord would have intended. A few other simple redesigns could easily address most of the other ‘cons’ listed below.

Lastly, they could make an astronomer living in Switzerland very happy if they would only include a nice, soft travel bag, in that not inconsiderable price.

For

  • Steady as a rock
  • Easy to setup and use
  • Feels like a product, rather than a prototype
  • Fine-motion controls
  • Tripod legs easy to adjust and spreader is excellent
  • Counterweight shaft not needed for Borg and other light OTAs
  • After altitude axis properly tightened, works well as a ‘push to’ mount for coarse aiming
  • Slow-motion controls great for fine aiming and manual tracking
  • No batteries required


Against

  • Natural play in the altitude axis
  • No way to easily adjust mount height once assembled
  • Restricted 30° range of slow-motion controls
  • Crude tensioning of altitude axis
  • Shape of various control hand knobs too similar
  • Azimuth clutch restricts choice of tripod
  • Tripod legs can get in the way when viewing at the zenith
  • Where’s the travel bag?



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