JMI NGT TELESCOPE 12.5 INCH SPLIT-RING NEWTONIAN REFLECTING TELESCOPE NGT12.5
JMI Reflecting Telescopes
JMI 12.5 inch Newtonian Reflecting Telescope NGT12.5
Item No. 165-12500
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Manuf. No. JMI NGT12.5
Special Order Item
JMI NGT Telescope 12.5 inch Split-Ring Newtonian Reflecting Telescope NGT-125
- Open truss Newtonian
- Split-ring equatorial mount
- Rotating nose assembly
- Built-in azimuth adjusting plate for easier polar alignment
- Compact size
- Fast one-man assembly
- Removable ring assembly allows greater disassembly with the largest component weighing 40 lb.
- Sidereal, Lunar, Solar and King tracking rates with both Northern and Southern hemisphere operation
- Dual control drive corrector with 0.3x / 0.5x / 2x / 4x / 8x / 16x correction
- NGC-MAX Computer digital setting circles
- CCD autoguider compatible
- Battery and AC power
- Adjustable focal point
- Snap-fit Serrurier truss rods
- JMI's celebrated quality construction
- Type: Newtonian reflector
- Mount: Equatorial split-ring
- Mirror: 12.5" f/4.5 Nova Optical Systems 2" thick Pyrex diffraction-limited enhanced primary (96% reflectivity), 2.6" diagonal enhanced secondary
- Power: 12vDC operation with included adapters or optional battery pack
- Weight: approximately 120 lb., the heaviest single component is 40 lb.
- Height: 64" assembled, 31" collapsed, Eyepiece height 59" at Zenith
- Width: 26"
- Depth: 29"
- Finder: 9x50 straight through
- The Telescope ships in a crate: approximately 34" x 34" x 37".
Frequently Asked Questions (FAQ)
- Rotating Nose Assembly for comfortable viewing of any part of the sky.
- EV-2n Focuser. (upgrades available)
- Extension Tube for 2" Focuser.
- 25mm 1.25" Plossl Eyepiece.
- 9x50 Finder Scope (straight-through) with dovetail mount.
- Piggy-Back Camera Mount for piggy-back photography.
- Off-Axis Counterweight for attaching to the piggy-back camera mount (2).
- Serrurier Truss Rods snap fit into heat treated, spring steel cavities.
- Adjustable Focal Point including three different nose assembly mounting positions for visual and photographic work.
- Sliding Counterweights positioned along the truss rods for fine tuning the balance (3).
- Split-Ring Equatorial Drive with 26" drive ring.
- 3-Point Large-Cup Flotation Mirror Cell.
- Primary Mirror Dust Cover.
- Integrated Optical Encoders for use with a "MAX" computer.
- NGC-MAX Computer digital setting circles with a 12,046-object database, Polar Alignment and Identify functions and a serial port. (upgrades available)
- Drive Corrector with dual axis control, 0.3x / 0.5x / 2x / 4x / 8x / 16x correction, North/south hemisphere operation and CCD autoguider interface (see warning).
- AC or DC Power with 110vAC/60Hz or 220vAC/50Hz (specify) wall transformer or 12vDC cigarette lighter adapter.
- Built-In Lifting Handle permits easy transportation.
- Latitude Adjustment with scale for fine adjustment of latitude setting. Adjusts from 30?8 degree
- Q. How long does it take to set up an NGT-12.5?
A. After a little practice, the NGT-12.5 can be routinely assembled in less than five minutes.
- Q. Does the rotating nose assembly make collimation difficult or impossible?
A. Contrary to erroneous reports on the Internet?Here are some comments from Tom Johnston who builds the NGT-12.5 telescope:
"Not only do I build the NGT-12.5 here at JMI but I also own one. I use it primarily to monitor faint periodic comets (using an ST7) for the IAU.
"There is a very simple pro and con relationship with the rotating nose on the NGT. This ability to place the eyepiece at a variety of comfortable positions in an enormous factor. The ease of use really cannot be realized until you've spent a night observing with it. In addition, the rotating nose allows you to place a heavy CCD camera in a more balanced and less stress producing position above the tube instead of hanging off the side. I personally would not give up my rotating nose.
"Here is the flip side. It is difficult to collimate IF you have never done it before because it requires that you find the best possible collimation position relative to the entire rotation of the nose. After you've done it a few times, it's easy.
"Before the scope leaves JMI, a laser spot must stay within the small white circle placed at the center of the primary mirror, throughout the 360 degrees of rotation of the nose. The spot may dance around a little bit inside the circle but it remains INSIDE. Using a Cheshire eyepiece, we then adjust the primary slightly until it is as close as it can get for the entire rotation. There may be a few places in the circle where the Cheshire indicator is not perfect...but it will be off only slightly. It's something you do not easily see visually or in a CCD image...but people like to talk about it anyway. The only problems I have heard of are when people try to collimate it like a normal (non-rotating) Newtonian."
- Q. Does the NGT hold collimation?
A. We have found that this telescope stays in collimation much longer than the average Newtonian. Most Newtonian reflectors need to be collimated every other time they are used. A recent floor model NGT-12.5 remained collimated over a span of at least 15 sessions. These sessions included two trips to major star parties (RTMC and Okie-Tex) and periodic comet observations and imaging in the mountains of both Colorado and Arizona.
- Q. How do you polar align the telescope?
A. There is a latitude adjustment screw that runs down the center of the telescope base. The screw is parallel to the polar axis and can be visually pointed at the celestial pole. This process can get you to within one-half degree of polar alignment in only seconds. The telescope can also be fitted with a JMI EZAlign polar alignment scope and, of course, you can use the good old stardrift method (see Document no. 8 in our Document Library).
- Q. Can the NGT be leveled?
A. All NGT equatorials have leveling screws and a bubble level located on the base.
- Q. How does dew affect the telescope?
A. All components of this telescope are rust proof. Water on the drive ring has no affect on the tracking.
- Q. How accurate is the split-ring drive?
A. Split-ring drives have little or no periodic error. In a random test of a polar aligned NGT-12.5, it held the Dumbbell Nebula in a 30 arc minute field of view for over an hour. Autoguiding feedback data from an SBIG ST7 CCD camera has confirmed this precision.
- Q. How does the wind affect the NGT?
A. All truss tube Newtonian telescopes that use a shroud are subject to windy conditions. Sudden wind gusts are more of a problem than sustained winds when imaging with a CCD camera. However, we believe that this telescope is not affected by wind any more than a standard German Equatorial Newtonian telescope. Tom Johnston, Production Manager and NGT-12.5 assembler, routinely uses production scopes (as part of JMI's Quality Control process) for gathering CCD images of periodic comets. He reports very good results in moderate wind.
- Q. Can the telescope be controlled by an autoguider?
A. With the proper cables and relay box (if needed) any autoguider can control an NGT-12.5 or NGT-18 telescope.
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