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Vixen Porta Alt-Azimuth Mount

Posted by Joplin Motisher-Chittenden   12/22/2006 08:00AM

I own a Vixen 80mm fluorite refractor that has been my favorite quick look telescope for about 5 years. I use it often in my yard where there are many trees that have to be avoided by moving it around. I have a small equatorial mount that is a hassle to set up and align in the yard since Polaris is blocked by a tree. I wanted a mount that would be light yet reasonably stable and much easier to set up. My ideal mount for these quick looks would be of an alt-az design with slow motion controls for high power viewing and a dovetail system to allow quick attachment. I settled on the Vixen Porta alt-az mount, which offers all of these features. Vixen Optics offers the Porta with a 70mm refractor for the same price as the mount alone and with an 80mm refractor for $40 more. I purchased the Porta and 80mm refractor outfit since the included rings and dovetail fit my 80mm fluorite. Thanks to Astromart the scope that came with the mount has already been sold for use as a guide scope.

I’ve been impressed with the performance of the Porta Mount. It is under 12 lbs. and easy to carry out the front door with or without a scope attached. Setup is a breeze and only the plastic accessory tray needs to be removed to fold up the mount. Both axes are easily adjusted to the right amount of friction using the handy allen wrench stored under a rubber cover on the mount. Motions are smooth with little stiction and there is no slipping out of position once the scope is aimed. Balance is more forgiving than with other small alt-az mounts I’ve used. I can switch from a 4 oz. eyepiece to a much heavier 1 lb. eyepiece and the scope stays on target. The slow motion movements are very accurate and smooth so it is easy to track and re-center objects at high power. The stability of the mount is excellent with damping times of 2 seconds at 175x (I should note that my 80mm weighs only 5 lbs. for the OTA and about 7 lbs. with 2” diagonal, finder, and eyepiece.)

The aluminum tripod included with the Porta mount is well suited to a mount of this size and provides reasonable stability if the legs are not fully extended. This may become a problem with longer refractor telescopes since the eyepiece position may end up being very low. In the case of my 80mm, the balance point is very near the focuser so this is not a problem. The Porta mount uses 3 socket head cap screws to attach the tripod to the mount rather than the single bolt that the Great Polaris series uses.

There are a couple things about the mount that could have been made better. The slow motion knobs appear to have metal shafts but they are actually one piece of molded plastic with metal reinforcement inside, and simply push onto the mount. The fit is too loose and this makes the otherwise excellent slow motions feel funky. The knobs can easily be replaced with higher
quality ones. The plastic tripod spreader works well now but I have to wonder about the long term durability of it.

The Vixen Porta mount is a good match with small scopes weighing about 10lbs or less and offers the benefit of both smooth motions and slow motion controls for high power tracking. It is best suited to short optical tubes (or ones that balance near the rear of the tube) due to the clearance between the mount head / legs, and to keep the eyepiece in a comfortable position. The dovetail saddle accepts Vixen style dovetails which are widely available. The Vixen Porta mount is one of the best small alt-az mounts available at a reasonable price. I will be using this mount a lot since it makes one of my favorite scopes even more fun to use.