MI-250 GO-TO
There is a New Question and Answer MI-250 wiki available on this site for MI-250 users
There is a new Question and Answer Gemini wiki for users of the Gemini-1/2 mount controller.

This mount is no longer being made or supported. Much of the content
of this site was provided courtesy of Larry Myers after he closed Mountains Instruments.
The Yahoo MI-250 user group is no longer functional. (All posting has been disabled.) All members, messages, files, Photos, databases have been moved to the https://groups.io/g/MI-250/ Users Groups. This is because the YAHOO user groups have been sold to Verizon Wireless, and will take them over in June 2017. Not knowing what this would do to this important group the owner and admins elected to move the group to Groups.io To post to the uses groups.io mi-250 message board using email use MI-250@groups.io You must you your email address you used on the MI-250 Yahoo group. You may change it by logging in to the web site https://groups.io/g/MI-250/ .
Please note that most of the below test is from the original Mountain Instruments web page. That web site and domain name is no longer in existence.
The Mountain Instruments (MI)-250 Go-To is a rock solid German equatorial mount that features a 7.5" RA and declination drive, matching worm and the Losmandy Gemini-1 System. This robust field mount was engineered and designed for SCT's, refractors, and Newtonians alike. For those requiring true versatility in an affordable package without sacrificing incredible stability, this is your mount.
The conical polar housing has been expertly cast in a #319 aluminum alloy, heat tempered, and then painstakingly CNC machined. Based in part on the Russell Porter designs, the polar shaft is also conical in shape for maximum stability. An internal slip clutch has been integrated for silky smooth movement of the RA and DEC axis. The RA and DEC worm/gears are diamond lapped for the ultimate smoothness. They remain as a matched set for the life of the mount. Periodic error is very low and smooth. Average 3-5 arc sec.
Like the polar base, the declination axis features a conical shape offering total rigidity. Additionally, a 7.5" gear and matching worm is utilized. The isolated counter weight shaft is independent of the declination shaft and is easily removed for transportation. The RA and DEC worm/gears are diamond lapped for the ultimate smoothness.

2009 model shown with a Stellarvue SV160 APO Triplet
background image by Jeff Herman
January 2010: Mount Evolution!
We are pleased to announce even more significant and exciting new changes in the design of the MI-250. These changes have been in development for months and are now a part of the standard package. Some of the changes took place earlier this year and others are brand new. All are a result of listening to you, our valued customers.
Amongst the most significant changes have been the actual axis. The RA and declination axis have been redesigned to enable the user to access and maintain the gears at home and with the simplest of tools or mechanical understanding. In the past, cleaning or re lubricating would require the user to send the MI-250 to Mountain Instruments (out of business now) for maintenance. This is no longer the case. Click here for more info.
Additionally, the face of the RA and declination shafts (the part you see) is expertly CNC machined from aircraft grade aluminum and then a hard, clear anodizing keeps it corrosion free. Classic CNC engraving has been machined as an added visual feature.
The 2010 model will also include a completely redesigned worm assembly. This will include larger bearing, and improved adjustment capabilities.
The Mountain Instrument deluxe saddle plate is now standard. The spring loaded deluxe version allows the user to "tip-tilt" the OTA into the saddle as opposed to lifting up and sliding down. A real plus for heavier OTA's. More deluxe saddle information Click HERE;
A tool is NO LONGER NEEDED to adjust the RA and declination clutches. Convenient clutch knobs are integrated into the new design.
The elevation and azimuth adjustment mechanics have been completely redesigned. The changes incorporate the means to remove azimuth lead screw backlash . Additionally there is no longer backlash in the elevation adjustment lead screw. Fine tuning in elevation and azimuth are effortlessly performed without the need of tools! Smooth adjustments in both axis. Positive ratchet type lock-down secures the elevation axis for trouble free and tool free use. Beautiful CNC machined knurled knobs lock the azimuth and help eliminate cable tangle. Both elevation and azimuth have been redesigned for heavier loads.
We have added finely engraved reference indicators in the elevation and azimuth axis for easier polar alignment. Additionally, large CNC'd "washers" have been added to the lower female rocker assembly to protect the powder coating surface that the knobs apply lock down pressure to.
The male rocker (shown below) has always raised questions for our customers. Here's the scoop:
PRO'S: Full surface contact. The mount is not supported on a "hinge" of any sort. There is no goose neck or Achilles heel in the mount design. Dampening is FAST! Stability is fantastic.
CON'S: Limited latitude range.
Although the design limits how far north to south you can travel with mount, the adjustment range is about 10 degrees. (approx. the distance from Santa Barbara, California up to Portland ,Oregon or for those of you on the east coast, Maine down to North Carolina!) We cut the angle so that your latitude is in the center point of that 10 degrees. In other words, lets say you live a 40 degrees latitude, you could travel down to 35 degrees or up to 45 degrees. If you move to another location, simply order another rocker from us for your desired new location. Four bolts secure it to the bottom of the polar assembly. If you know that you will be needing a second rocker at the time you place your order, we'll give the second rocker to you at no additional cost (otherwise they cost $175) just for reading this!
The wear resistant powder coated castings, with black anodized aluminum, flawless lines and fine craftsmanship, make it as beautiful to look at as it is to use. And the best for last.......Timely delivery!
An MI-8P pier used to be available for use with the mount for field use.  Of Course it is no longer in production.
All of the described new features will be available in early 2010.
Polar Assembly
  • Up to 85 pound payload capacity (depending on moment arm of OTA and type of pier)
  • Easy 5 minute set up time
  • Matching precision ground worm
  • Conical shape for maximum rigidity
  • 7.5" RA drive
  • Conical polar axis
  • Major polar axis bearing-3.74"diameter
  • Variable friction slip clutch
  • Beautiful powder coated and black anodized finish
  • Redesigned altitude and azimuth adjustments!
  • Total RA (conical section) weight-38 pounds
German Declination Assembly
  • Conical shape
  • 7.5" DEC drive
  • Matching precision ground worm
  • 3.74" major bearing
  • Easily secures onto polar base in less than 2 minutes
  • 30 pounds total-. (not including c.w.'s or shaft)
  • Isolated and removable counter weight shaft
  • 20 pound counter weight (2 ea)  10 pound weight available
  • Same attractive powder coated and anodized aluminum as polar base
  • Deluxe saddle plate standard-Accepts all Losmandy, AP, and Cassidy male dovetail plates
  • Easy access to RA and dec clutch adjustments. No tools necessary
  • The Gemini Servo System Features Level 4 system included.
This site is now being maintained by Tom Hilton
Please contact him through the Yahoo MI-250 Users Group.
Copyright 2010-2015, MI250.com and Tom Hilton    All Rights Reserved.