Vixen Porta Mount
Submitted: Sunday, 10th December 2006 by Andy Jackson
In the search for a compact portable mount for my William Optics Zenithstar 66SD, I decided I didn’t need an equatorial mount, just a simple alt/az rig that could be quickly taken out the back door for short observing sessions and also be small enough to take away on holidays and trips into the country. The main contenders for me seemed to be the Skywatcher AZ3, the Vixen Porta and the William Optics EZTouch. I had no first hand experience with any of these but had read many articles and forum posts on the internet. The AZ3 and Porta both had slow motion controls which I liked the sound of. The EZTouch had a greater load capacity as well as the ability to mount 2 scopes at once which seemed like a good idea also. The prices varied from under $200 for the AZ3 to over $800 for the EZTtouch. The Porta was under $400. In the end I decided I didn’t need the extra capacity and cost of the EZTtouch and I preferred the design of the Porta over the AZ3.
The Vixen Porta mount is available as a stand alone mount or as a combination package with various optical tube assemblies included such as a 130mm Newtonian reflector, 80mm achromat refractor, 80mm ED or 100mm ED refractors. It is rated for telescope tube assemblies up to 5kg. The complete Porta mount with tripod but without telescope weighs 5.5kg.
I ordered the mount only from Astro Optical Supplies over the phone. I found them to be very helpful and efficient with a very competitive price.
I have no connection with Vixen or Astro Optical Supplies other than being a customer and this review simply represents my own personal opinion with a view to helping to inform my fellow amateurs in the amateur astronomy community.
The package arrived safely and promptly. There was slight damage to the cardboard carton on one of the corners but no damage to the mount inside. Everything was well secured in the box in foam mouldings and plastic bags. A comprehensive manual is included. The manual is available as a free download in PDF format at Vixen Optics. Although Vixen is a Japanese company the mount is made in China, no doubt to reduce costs. The mount does appear to be well made with no glaring ugly bits or signs of poor quality control.
My initial impressions were positive. I liked the simple compact design and the well executed finish. The textured white paint seems to be reasonably tough and does not show marks or fingerprints like a smooth gloss finish. The tripod is height adjustable with simple threaded toggle clamps. The range of adjustment measured from the centre of the altitude axis to the floor is 865mm to 1365mm. Measuring to the top of the tripod, the range is 710mm to 1210mm. The plastic tripod spreader bars are hinged to a short threaded central post that accepts the small accessory tray, secured by a round hand nut. My first thought was that they had skimped on the accessory tray as it is quite small and light and does not improve the stability of the mount in any way like on some other Vixen tripods. On the other hand I soon realised that the small tray size means the tripod legs can still fold in to each other without having to remove the tray from the spreader bars. This is consistent with a design that can be left set up ready to go and makes getting the tripod and mount with telescope easier to get out the door in one piece. The tray is still big enough for a couple of eyepieces and lens caps. It would not be too difficult to make a larger tray if required.
The altitude/azimuth head consists of a “L” shaped aluminium casting with 2 friction clutches mounted perpendicular to each other. The friction clutches are fixed but the friction pressure or feel can be adjusted by means of a small hex head grub screw on each one. What makes the Porta unique to my knowledge is the combination of slow motion controls with the friction clutches. This means the telescope can be pointed roughly by simply moving the tube assembly manually by means of the sliding friction clutches. Then fine positioning and tracking of objects is achieved via the slow motion controls (120 teeth worm gears) on each axis. In practice this works very well. Set up is as simple as walking out the back door with the complete telescope and tripod in one hand. The two plastic knobs for fine control are the same and simply slide on to the D shaped ends of the shaft. Either end of each control shaft can accept the knob allowing the user greater convenience depending on your preference.
Mounting optical tube assembly
The Porta uses the standard Vixen dovetail clamp which has been copied by other manufacturers and as such has become one of the industry standards. There is a main hand operated set screw to lock the telescope dovetail in to place with a secondary smaller set screw as a safety back-up. The clamp plate can be removed from the mount to reveal some threaded holes (¼” x 20tpi and 8mm x1.25) which would allow for customized mounting options. Also the clamp plate can be repositioned to other angles with relation to the control shaft.
The William Optics Zenithstar 66SD comes supplied with a mounting foot that is tapered on the sides and supposedly Vixen compatible. However I found that although this mounting foot works well when using the ¼” x 20tpi threaded holes with a standard photo tripod it is really too short to use as a dovetail on the Porta mount. Vixen compatible dovetails are available from most Astro shops but I chose the cheaper option of DIY. I used a piece of 10mm thick aluminium bar, 100mm long and 48mm wide and filed the sides to create the angles to fit into the dovetail. Two countersunk holes attached the bar to the telescope and I was in business.
As you can see the dovetail bar just clears the focuser knob but still gives a small range of fore and aft movement within the dovetail clamp to allow for balancing the telescope tube. The little 66SD is short and light so balancing was never critical but it may become more so with a 100mm f9 scope. If you buy the mount as a package with a Vixen scope it will most likely include a pair of tube rings which can be adjusted to balance the scope.
The above photo shows the scope mounted and also the nifty method used to keep the supplied hex keys with the mount. The black rubber cover pulls away to reveal a shaped indentation with 2 small magnets to keep the hex keys in position. The smaller key can be used to adjust the friction setting of the clutches and the other one fits the 3 screws that hold the mount head to the tripod.
Personally I like the simplicity and convenience of simple alt/az mounts but for those that wish to this mount can be fitted with motors for hands free operation (microslew for Vixen Porta by www.jimsmobile.com) or even Go To electronic control (AWR go to, www.scsastro.co.uk). However if you chose that route there are also many other mounts available.
This mount provides a great blend of portability and ease of use and has no real faults or problems in my experience to date. For grab and go convenience it is a good choice for smaller telescopes. If you intend to use a scope around the 5kg upper limit for this mount you may find the tripod becomes the limiting factor for vibration free viewing especially at higher magnifications. In this case the tripod legs could be improved with wooden replacements however this would naturally increase the weight.
Little things that could be improved (nit picking)
Since I bought this mount I have become aware of another option in this class of mount. Frontier Optics are agents for the Universal Astronomics Micro-star deluxe and Macro-star deluxe. Check them out at www.frontieroptics.com.au
Hope you like the review, I am interested to hear from others who have experience with this mount.