JMI NGT-18  (2001)

All round excellent piece of hardware. Compact enough to easily transport, though it takes two grown men to lift (unless you really want to take it down to smaller components). Tracking makes the DOB guys jealous at star parties.

NGT-18

Specs

* optional or upgrade item at the time I obtained this scope, check with JMI for current specs

Optics Mirror Galaxy Optics  
18", f/4.5, 96% reflectivity, 2 inch thickness (about 55 lbs)
18 point flotation cell
  Secondary 4" enhanced (I don't know the manufacture of mine)
  Eyepiece 1.25" Celestron 25mm NexStar Plossl
Finder Optical 9x50 Celestron (straight), mounted with Orion hardware
  *1X Telrad with an AstroSystems dew shield
Focus *NGF-DX1 2" Crayford, 1.9" lift, 8 lb capacity
Two setscrew eyepiece capture
  *Motofocus Variable speed from the Hand Control or Digital Read Out (DRO) unit
  *Encoder Required for the DRO unit
Electronics Command Center Sidereal and Lunar tracking rates only
Hemisphere selection
Hand Control button reversing
One jack for either the Hand Control or SBIG standard autoguider
  Hand Control 2X & 8X axis corrections
Variable speed focus control
SBIG standard autoguider jack
Red LED chart light
  *Digital Read Out Separate hand unit for controlling the focus on encoder equipped JMI focuser
Variable speed
Reports a number as you run back and forth:
    Not absolute - zero can be set at any focus location
  *NGC-Max Digital setting circles
12,000 objects
Various catalogs and tour modes
RS-232 input for external computer connection
Assembly Truss Rods 8 Serrurier Truss rods
Stainless ball and spring steel snap cup at bottom (no removable hardware)
Threaded knob at top (not captive)
Three heights to setup for visual use or photography
  Counterweights Three threaded weights hold the mirror cell in the tube
(At the time we got this scope, two different weight sets were available - we got the heavier to counterbalance the SBIG camera)
    Four sliding counterweights are provided for the truss rods, we added 4 more to compensate for the heavier bottom weights.
    Nose ring counterweight
  Mount 36" split-ring design - horizon to horizon viewing with no obstructions
Lead shot filled to keep the ring in firm contact with the drive wheels
  RA drive Single motor running two drive wheels connected with nylon chain
Adjustable tension
  DEC drive Tangent arm / screw design  (requires resetting every couple nights)
  DEC bearing 2" bearings, adjustable tension
  Upper cage Rotating nose ring - position eyepiece at the most comfortable location for use
Piggy-back camera bracket opposite of focuser
Handles for easier assembly and moving the scope around the sky  (also handy for hanging the Hand Control on)
  Cooling fan Built into bottom of tub
  Base Four leveling feet with large knobs
Bullseye level
Power panel, including built in batteries
Latitude adjustment
  Mirror cover Kydex plate with handles - wedges fairly solidly into tub
3" and 6" openings to stop the scope down if needed
  Secondary cover Molded Kydex - held in place with three thumb screws
     One of the few Newts I've seen with a provided secondary cover
  *Lightshroud Black Lycra type material, elastic ends keep it in position
  *Light baffle Nose piece extension to block off-axis light out of the focuser
  *Wheelbarrow Wheels and handle to move the scope, bolts solidly to base
Physical Weight Approximately 250 lbs (heaviest part is 75 lbs)
  Height 80" assembled (eyepiece is 76" at zenith)
30" collapsed
  Width 36"
  Depth 30"  (will fit through a standard doorway)
  Latitude 30 - 55 degrees  (low latitude base wedge available)
Power Internal Built in batteries will power scope for a couple nights
Low battery alarm
  External 12v (110v wall wart and 12v cord provided)
  All cables are terminated with either a Jones Plug or RJ connector.
Scope power runs RA/DEC motors, cooling fan and the NGC-Max. 
Focuser and DRO are 9v battery power only.

Pros/Cons

+ No tools required for normal setup

- Truss rod knobs are not captive

- Leveling feet use a cheap dimpled sheet metal plate (think big fender washer) on the ground under the bolt.  I tend to leave them behind and have to retrieve them.  So far I haven't lost any...

+ Tracking - not many scopes this size are motorized

+ Galaxy mirror  - Wow.  It makes common items take on new life, such as, M-42 - looks almost 3D and it seems you can see layers in it, M13 - see numerous individual stars across the entire cluster, ...

- Weight - about 250 pounds.  Tough to get in and out of a truck by yourself, even with the wheel and handlebar option.  Lower vehicles are much easier to load

+ Stability - I've never used a scope that is as stable.  It is much more stable than my LX-200.  Four leveling bolts ensure a solid base, split ring is filled with lead shot to keep it tight to the drive wheels no matter where the scope is pointed, full thickness mirror adds another 50 pounds, three heavy counterweights (available in two weights, we got the heavier to counterbalance the SBIG camera) under the mirror.

+ Easy to break down - mirror cell is held in by the counterweights, spin them off (don't smash your hand under them) and the cell lifts out of the tub, handles are welded to the cell.  Remove two knobs on the base and the split ring and tub lifts off.  All electrical connections are either a Jones plug or 6-conductor phone jack.  Note - since the mirror is normally protected by the tub and cover some means of protecting the mirror needs to tended to when it is removed.  I only break it down this far for maintenance.

- Declination drive is not continuous.  Every couple nights I have to take a few minutes and center the declination drive screw.  There is no quick way, you just mash down the declination button on the hand control and watch it for a while until it is back to center.     

+ Cooling fan built into the bottom of the tub.  I rarely use it as I tend to get setup early enough to cool before dark, when I have used the fan it has quickly cooled the mirror and I haven't noticed any fan induced vibration in the view.

+ On-board batteries eliminate having to drag an external power source along, low voltage alarm alerts when a recharge is needed.  They can easily run the scope for two nights.  Powers the scope, fan and digital setting circles. 

+/- Wheel and handlebars bolt on design is solid, but time consuming to install/remove and requires me to sit on the ground to get to the bolts.  I generally leave the wheels attached, and also occasionally leave the handlebars on and I just have to be careful I don't bang my shins on them in the dark.  Wheels are on the smaller and thinner side so soft and rough ground both present difficulties.  Using this option does allow me to move the scope by myself. 

+ Rotating nose ring - allows the focuser to be rotated to any position for ease of use.  However, the collimation does change some as the ring is rotated.   Visual use is great, if I look and see a collimation error, a small rotation of the nose ring usually snaps the collimation right back in.  For imaging I determine where the camera will be and precisely collimate to that nose ring location.

+ Large split ring design - eliminates periodic errors.  What little tracking error exists is smooth and predictable.

- Large split ring is not exactly round - leads to aiming errors with the digital setting circles.  Tracking rate changes some as the scope moves across the sky, but is easily handled with a good autoguider while imaging, not even noticeable with visual use.

+ Digital Read Out (DRO) - very handy for manual focusing when imaging.  This version doesn't report back an absolute focuser position so automating focus is very much a hit and miss (mostly miss) because of this. 

JMI has Smart Focus - an additional control unit for the DRO that reportedly works very well and integrates to the auto focus modules in most CCD programs - Maxim DL, CCD Soft, etc..

+ NGC-MAX digital setting circles - a nice, but not absolutely needed, feature.  I enjoy star hopping and hunting objects, as I can locate most objects in a couple of minutes.  About half the time, I don't even install the computer control.  The rest of the time I use it and it is somewhat enjoyable.  I do have to admit it is a great system for public star parties, provided you have the time to align/calibrate the computer before the public starts lining up (the public masses have to look NOW, not after you get things working like you want).  It is an easy system to set up and use, but you do need about 15 minutes or so to get it there.  Due to the mount not being precisely circular I find that I have to keep refining the calibration throughout the night. 

For more info: Jim's Mobile

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