VIXEN "PORTA" ALTITUDE AZIMUTH MOUNT

What is the Porta Mount and when do we recommend it?

When do we not recommend it?

Porta Mount Features and Specifications

Overview: What is the Porta Mount and when do we recommend it?

The Porta is a simple to use gear driven single tine fork mount sold as a set with a lightweight tripod, the set being designed for use with compact terrestrial or astronomical telescopes (such as the TeleVue 76, TeleVue 85, Leica, Orion 80 ED, etc.) for terrestrial and for visual astronomical uses. With the gear drives it makes it a simple matter to track a planet or a ship on the horizon precisely simply by turning the elevation and or azimuth control handles.

Right: Vixen Porta Alta Azimuth Mount shown as provided with aluminum Tripod and Accessory Tray (77,194 bytes)
Click on the image to see enlarged view (120,555 bytes).

At first glance we thought the stand was so well finished and assembled, rigid and free of slop that we thought it was made in Japan. But this mount is designed by Vixen Co., Ltd. in Japan, then manufactured in China with the cooperation of Vixen engineers. The Porta Mount provides better rigidity pound per pound, and can weigh less than some other moderately priced platforms due to the use of advanced materials, better components and design.

Porta is made up of two identical clutched worm gear drive sets. The gear drives one platform left or right (azimuth). While the other drive mechanism in the fork tine permit fine control up and down (elevation). Hence the term Alt-Az for short. Each gear is provided with a handle to permit a full 360 degrees of rotation by the worm gear and thereby the fine motion of the telescope up down or left and right. With its gear drives, and canted single tine fork mount arrangement one can access any area of sky including zenith, and then manually precisely track a celestial object across the sky. The telescope can traverse up to directly overhead, and down limited only by those longer telescope optical tubes which might reduce the depression angle. Slip clutched permit the operator to simply move the telescope manually up or down without using the fine gear control.

If one wishes to reposition either gear control handle then one can disassemble either elevation or azimuth axis from the geared enclosure, rotate it, and then reinstall it in an different orientation. For the convenience of the user, two Allen wrenches are provided (4 mm and 3/16 inch) in a compartment hidden beneath the azimuth axle platform's snap on rubber cover.

The entire head assembly is attached the provided aluminum field tripod by means of three ¼ inch 20 tpi threaded bolts; it would be nice if Vixen were to change this with hardware that would provide a way to quickly remove the Porta head and install it onto a more compact or conventional photo tripod for example. Furthermore, with the present arrangement there is no way to adapt the Half Pier to minimize leg spread or provided added height. Company Seven has conveyed these concerns to the manufacturer but if we experience enough interest then we will manufacture the adapter so that customers who buy the mount from us may use their Porta Mount on third party field tripods or other stands.

The telescope is installed onto the Porta mount by means of an optional Dovetail Plate which slips into the Saddle on end the elevation fork tine. This works well with most telescopes that incorporate either a straight through view orientation (such as some of our spotting telescopes), and this will work fine with telescope optical tubes that are provided with mounting rings. However, some telescopes that position the telescope eyepiece at ninety (90) degrees to the optical axis and that also have no provision for rotation will be incompatible with the Porta Mount. Please contact Company Seven if you have any questions.

Left: Porta Mount Saddle shown with optional Dovetail Plate AM-AD-2661 installed (48,708 bytes)
Click on the image to see enlarged view (101,780 bytes).

The Vixen Dovetail Plate part number AM-AD-2661 is on of the plates we can recommend to install most common small reflecting and refracting telescopes that employ two separate mounting rings. One ring is attached onto each end of the AM-AD-2661 to support the telescope. The mounting rings are loosened enough to permit sliding the telescope lengthwise back and forth until a reasonable balance is achieved, then the rings are tightened. The AM-AD-2661 is cast aluminum, painted to match the Porta mount, and other popular Vixen German Equatorial Mounts.

Company Seven also offers an adapter plate to facilitate the installation of telescopes made by TeleVue Optics, Inc. onto the Porta Mount. This plate attaches onto a TeleVue telescope's Ring Mount and makes it easy to move the telescope from TeleVue's Telepod or Gibraltar mounts to the Porta mount, or from the Porta Mount onto Vixen Equatorial German mounts. When one lays the plate over the cradle of the Telepod head, Gibraltar Mount, Porta Mount and other similar mounts you can center it so that a Wing Nut Bolt can come up from below. It also makes it a simple matter to install the telescope onto the Vixen German mounts that incorporate the dovetail plate mechanism. The plate is machined of aluminum stock, and is black anodized. This Plate is part number AVX-1011.

Right: two AVX-1011 Adapter Plates shown to illustrate top and bottom (34,803 bytes)
Click on the image to see enlarged view (94,037 bytes).

Company Seven recommends the Porta Mount to accommodate payloads including:

• terrestrial applications: birding, panoramic uses, etc.
• telescopes weighing up to about 10 lbs. / 4.5 kg, this can include
  
  • Refracting telescopes up to about 100 mm aperture *
  • Catadioptric telescopes of up to about 150 mm *

  * there are factors acting upon a mount affecting its suitability including: payload weight and length (torque), payload area and profile exposed to winds, desired tracking accuracy, tripod resonance's, etc. What are most important to the user is how rigidly the mount holds the payload, how smoothly it tracks (amplitude and smoothness of the periodic error of a gear), and how well it overcomes the moment imparted by the load. The final operating weight put onto a mount can also depend on how the instrument is to be accessorized.

When do we not recommend it?

Porta mount is a suitable choice for many of our popular compact refracting telescopes. It is lightweight, easy to set up and use, and can be used ideally for terrestrial as well as visual astronomy applications. However, for uses in astronomy as one approaches those higher magnifications necessary to see meaningful details on the planets (200X or more) it then become more and more challenging to manually move an Alt-Az mount simultaneously in both elevation and azimuth over long observing sessions. If you seek to observe the planets or do other operations which require high magnifications, or if you wish to share the telescope with several others or children, or if you hope to become involved in astrophotography, then we do suggest you place the telescope onto a motorized German Equatorial mount that will provide a much easier capability to stay on a target in the sky.

Of course the downside of German mounts is that they are heavier and more complicated to set up and use than Alt azimuth mounts, and so you will find there is no one perfect solution for every problem. For those who seek a more refined and precise lighter weight German mount then we suggest the Vixen GP-E mount.

Porta Mount Features and Specifications