JMI NGT-18


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Brand and Model:JMI NGT-18
Price ($USD):12,900
Type:Newtonian
Attributes: un-checked Go-To un-checked PEC
Aperture:457mm (18")
f Ratio:f/4.5
Focal Length:2000mm
Finder:9X60
Electric Power:Batteries built in
Mount:Split Ring Equatorial
Tripod:N/A
Weight (lbs):220 lbs.
Dimensions (w/h/d):75 X 30 X 36
Description:Standard Equipment:
Rotating nose piece for comfortable viewing at any angle. One step up needed for zenith viewing.
Digital setting circles.

Non Standard but not really Optional Equipment:
Light shield
Truss Shroud
Wheels & handlebars if you are going to move it often.

Other features:
Very stable with adjustable friction for RA & DEC to withstand wind.
One person handling & setup (~ 40 minutes with collimation.)
No tools needed for setup.
Compatible with Sky
Hand controller designed for auto tracking with ST-7, ST-8 etc.
Not a Go To scope.

Vote Highlights Vote
JMI NGT-18
For visual use, this is a wonderful scope - some of the best views I've
ever had. The optics deliver well. You'll have to be satisfied with
"close" collimation, though; the rotating nosepiece does lose collimation.

The mount tracks very well, almost by default. The "split ring" of the
equatorial mount is 3' in diameter - so it's like having a 36" gear on
a more common design! It's only *bent* round, though, not machined; so
there's going to be more random tracking error to deal with for astro-
photography.

The declination gear is a lot smaller, though I never found that to be a problem.

What *is* a problem is balance. The split ring design means that there
is a lot more tube length above the declination axis than below it -
about 4x as much. So a pound at the eyepiece requires 4 pounds of coun-
terweight at the bottom of the tube - more if you need to add weight op-
posite the focuser.

This doesn't cause a problem changing eyepieces - there are sliding weights
on the truss tubes to give you fine control of the balance.

This, though, makes the scope unsuitable for astrophotography, although
some such work *has* been done with them. Further, there's no good way
to attach a guidescope, which means more equipment at the eyepiece end
for guiding, which means a *lot* more counterweighting ... it quickly
adds up to too much. A self-guiding CCD camera might work out well,
though.

In short, if you're a visual observer who, like me, doesn't like pushing
a Dob around, the NGT-18 is a great alternative.

Overall Rating: 8
Weight: 3 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.254.60)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=39439


JMI NGT-18
Le ngt 18 est un télescope réservé a un amateur déjas expérimenté.Car pour l'exploiter au maximum il faut revoir de
nombreux détails relativement faciles à corriger.1) Recentrer
le secondaire afin d'obtenir une tache de diffraction correcte et faciliter la collimation. 2) Faire reposer le nez tournant sur
8 cales de teflon et non 4 comme prévu.Modifier les pates des roulettes afin que les 8 maintiennent la partie mobile contre la partie fixe sinon un léger voilage se produit lors de la rotation du nez. 3) Revoir le support du mirroir secondaire en le rigidifiant afin que le mirroir repose sur 3 points à 120 degrés et s'assurrer qu'il n'est pas cintré. 4)Utiliser un correcteur de champs.( télevue par exemple). 5) Pour équilibrer le télescope lorsque j'utilise de lourds accessoires, j'ai fabriqué des contrepoids en plomb que j'ai fondu de telle façon qu'ils s'intégrent entre les vis de reglage du mirroir primaire.6) J'ai mis 3 vis calantes à 120° au miroir primaire afin d'éviter un astigmatisme lors d'observation prés de l'horizon.
Une fois ces modifications faites et une soigneuse collimation,le ngt 18 devient un vrai régal; La rotation du nez n'entraine plus de détérioration de l'image visible à l'oeil.Il est vrai que lors d'observation planétaire à haute résolution je préfére remettre l'oculaire dans la position oû j'ai éffectué la collimation.

Overall Rating: 8
Optics:8 Mount:8 Ease of Use:9 Value:8
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.226.237)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=567310


JMI NGT-18
Perfect collimation is difficult with rotating nosepiece.
Big mirror means it is slow to cool down.
Can be set up easily by one non-short person.
Can be transported by one person without too much difficulty over lumpy ground if you get the wheels & bars.
Rotating nosepiece ensures a comfortable angle.
Good tracking but a lot of backlash comes in when the chain drive stretches.
Variable clamps allow for adjustment for wind conditions and personal preferences.

Overall Rating: 8
Optics:9 Mount:9 Ease of Use:7 Value:8
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.190.1)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=466421


JMI NGT-18
This scope sucks! I curse the day I bought this sucker. You want to image with this scope? Well, dream on.

Overall Rating: 2
Optics:7 Mount:1 Ease of Use:1 Value:1
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.60.223)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=393901


JMI NGT-18
I own my 18 for almost 10 years and use it often (barely once a week),
i just modified a couple details allowing me to align it easily, (ex:the alt.
adjustment screw...) Otherwise it's an outstanding scope with a fairly good
optics and a stable mount you can rely on for serious astrophoto or ccd
imaging.
advice ! always set it up correctly...collimation, polar alignment, balance !

Overall Rating: 8
Optics:8 Mount:8 Ease of Use:10 Value:9
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.52.169)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=139856


JMI NGT-18
The rotating frontring can't maintain collimation and collimation is also affected by turning the front end. The frontring is the main culprit why I didn't enjoy this scope. In addition to the collimation problem it's much too heavy. Putting it on the poles is a pain in the arse for one person! That you have to attach the poles from the side only makes it worse. I recommend to throw the frontring away and to make your own! Use fiberglass to make it lightweight and make sure that you can put it ON the poles (of course you have to change the clip attachment system)!
Another problem with the NGT 18 is if you add a lot of weight like CCD you've got a serious balancing problem.
Another huge problem is polaralignment, I really can't understand how one can build such a scope without proper mechansims for polar alignment!
To put it in a nutshell, I wouldn't buy the NGT18 again and I can't recommend it for a person who wants to own a transportable Newton suitable for astrophotography.

Overall Rating: 5
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.225.51)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=39440


JMI NGT-18
Really great design. It's a shame that it was compromised by the poorly designed rotating nosepiece. Collimation at f4.5 is very critical. As the nose is rotated around the difference in sharpness can be seen. The people at JMI I talked to don't want to acknowledge the problem. To them it is "close enough".
I am working on my own retrofit bearing for the nosepiece. Everything else about the scope is pretty awesome. It is a one-man transportable fully-functional observatory.

PFK97@yahoo.com

Overall Rating: 9
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.24.122)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=39438


JMI NGT-18
Rating 9.0. Very nice scope. Easy to use, One step needed at zenith by average height man. Nice to have equatorial tracking on such a large aperture Newt.. Galaxy optics are excellent. My only complaint about scope is the collimation does not stay precise when nosepiece is turned which it must be when observing different areas of the skyl

Overall Rating: 9
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.246.193)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=39437

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