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Gemini Mountegra - Single Arm EQ Fork Mount
Submitted: Tuesday, 19th February 2008 by Dr Dietmar Hager

The design unites highest aesthetic demands as well as a maximum request for stability and strength. Also Mountegra’s flare displays reliability and that’s what it’s capable to offer!


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Gemini Mountegra

Aluminium ensures rigidity in those places where it is asked for with a thickness of up to 20mm  - this provides the mount with high stability where it is necessary: at the bearing and it’s housing and at both arms, the vertical and horizontal one. The gear is made of the finest bronze, the worm made of high-grade steel.

Adaptive Fork Mount

Representing the worldwide first most intelligent innovation in mount-desing, Mountegra offers it’s users fully adaptable mount-arms, that is the horizontal and vertical arm.

This means that one can move the horizontal arm in an extent of 20 cm of amplitude in it’s RA fixation so that the main center of gravity happens to be projected exactly over the base plate. One checks this with a torque key (provided by Gemini) which becomes connected directly to the worm (while the drive system is not activated!). The value read on the display must be equal in the two directions of rotation. Once this is done optimal balance is achieved successfully. There is no need for any counter-weights.

After this the telescope is to be moved in a 90° position (so that the scopes longitudinal axis is orientated widely horizontally) and the scopes are moved forward and backward in their tube-rings until one reads equality with the torque key attached to the worm again. Furthermore the vertical arm can also be pulled out in a range of 20 cm so that one can accomplish observation in the most comfortable way!

The elegant 3 - part handle (found on the short arm edge) serves as a lever for to adjust the mount horizontally and vertically as described above.


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Polar Alignment

According to the illustrations the screws which hold the mount down to the base-plate which is supposed to be attached to the pier can be completely opened up - don’t worry - Mountegra and the scopes will stand still as a rock and will definitely not move anywhere! The common center of gravity (mount and scopes) remains in all cases exactly inside the base plate!

To adjust the azimuth and the polar height in order to find a perfect polar alignment there are 2 wheels which display exact measurements in arcs of a second so you can easily make use of any polar alignment procedure you want. If you calculate the misalignment in some 2.5 arc minutes e.g. you just turn the wheel until this amount has been reached!


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Altitude and Azimuth adjustments
Smooth running granted with Pulsar, Stability

Mountegra is best driven with Pulsar. This guiding system is the most appropriate for any Gemini mount. It was dedicatedly created for Gemini mounts.

Under a magnification of 500 I already tested Mountegra`s reliability in tracking. Mountegra shows a completely pure drive without any pendulum faults, without any jumps or fluctuations! A most satisfying performance in tracking! Maximum goto speed is 3°/sec. A higher rate is possible but not recommended by Gemini.

If one bumps the mount on any place you like while observing with 500 mag, the picture swings for only some tenth of a seconds up to at most 2 seconds!

First Light Photography

April 2006: Set-up: TeleVue 0.8 Reducer and 9 " TMB on SXV M25C. Guiding tests with SX Guide-cam attached to 4" TMB prime focus.

There is absolutely no backlash in RA. In Declination there is some - which can easily be corrected by making use of Pulsar’s software routine where you just enter the amount of backlash-time in seconds. When tracking speed is activated there will never be any delay in guiding impulses given by the guide-controll software! Functionally there is no backlash in declination, too! The Guiding works completely without any problems and reliably. The stars remained pin point like even at exposure times up to 20 minutes.

Images taken with this mount can be found on my web-site.

Resources and Links

Review by Dr Dietmar Hager (Dietmar). Discuss this review on the IceInSpace Forum.

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