I was already stuck in the "SCT vs. Big-Dob" dilemma. Hoping to get
into CCD work some day, I was coming very close to ordering a 12"
LX-200. There's a bit of a story about how I wound up with this instead;
if you ask me in person, I'll tell you about it.
So the JMI NGT is, as I see it, a great compromise scope between a
Dob and an SCT. It's like a little of both. It's a 12.5", F4.5
truss-tube newtonian on an innovative split-ring equatorial mount. It
has R.A and declination drive motors. And it's all metal (with a bit
of plastic) -- there's not a splinter of wood to be found on it. The
mirrors are made by Nova Optical Systems, with enhanced coatings by QSP.
I took delivery of it yersterday morning, just in time for the trip to
Lassen. No, I won't be held liable for adverse conditions at Lassen
attributed to this acquisition -- other people are bringing new gear as
well!
Last night, I set it up out on my sidewalk, under the orange
street lamp, in the shadow of a small tree, with canyon-like horizons.
I did a rough polar alignment using a (magnetic) compass and by setting
the calibrated latitude scale from a topo map.
The only bright, quick, and easy objects I could see from that location
were Alberio, M13, & M57. The sky was bright and hazy, and the city
lights reflected off clouds in my only window to the extra-
terrestrial. From my north San Jose home, the seeing basically wasn't.
Alberio and it's partner, at 158X, readily separated even though it
looked like two hazy, colored blobs. M13 at 53X was as bright and
clearer than in the SJAA-owned 13.1" F4.5 Coulter Oddyssy I've been
using recently. Stars showed less coma in the JMI than I've become
used to in the Coulter.
Under last night's conditions, I knew that seeing more than a
recognizable blur on M57 would be unlikely. I could just make out it's
ring-ness at 53X, and last night's poor contrast made it a more
difficult object at 158X. But I had another test in mind that didn't
really involve the optics: I wanted to test the drive and the stability
of the mount.
Getting the ring nebula carefully centered at 158X, I went for the
absurd 476X view. A fuzzy, low-contrast blob, vaguely hollow, almost
filled the field of view. Adjusting the crayford-style focuser caused
no image shift, and resulting vibrations were damped almost as soon as I
let go of the knob. It was easy to get close to the eyepiece without
disturbing the view.
I set a timer to beep at 6 minute intervals. My goal was to see how
much the image drifted in the 30 minutes of a typical film exposure. I
had to make one declination adjustment at 21 minutes into the test,
which was less than 20% of the eyepiece field of view. But even
without that adjustment -- the ring would have stayed in the eyepiece
for the entire half hour. That's much better than any other mount I've
ever had in my posession.
I've heard a lot of rumors about columnation problems with the JMI
'scopes. So I took it back inside and played both with a cheshire
eyepiece and a Kendrick laser columnation tool. I couldn't see any
error in the cheshire no matter how I rotated the secondary assembly.
The laser columnator showed a little error, however. There was less
than a beam's-width error in the spot where the laser hit the primary,
but back at the scale on the columnator, It was nearly impossible to
keep the beam perfectly centered throught the roation of the secondary
assembly. However, I should say that the none SJAA Dobs I've borrowed
held columnation this well -- from just movement in the altitude
direction. I'll see if this becomes an issue under actual use.
I'm looking forward to testing this 'scope under darker skies, and to
see what I can get on film with it. I'm excited about this new
instrument, and I hope some of you joining me at Lassen can help me get
the most out of it.