First Light: 14.5" f/5.4 Newtonian

From: Axel (ritesh_laud_at_hotmail.com)
Date: 07/05/04 

Date: 5 Jul 2004 01:53:42 -0700

After a long wait, I finally took delivery of a 14.5" f/5.4 Dobsonian
from NightSky Scopes. Here's a brief overview of the scope and my
first light last night.

I had NSS build the structure and provide the secondary mirror, while
I sourced the primary from R. F. Royce. Upon delivery and assembly,
the scope appeared physically much larger than I expected. Even
though on an intellectual level I knew exactly how tall and heavy it
was going to be, I still did a double take after seeing that the
focuser was a good six to eight inches above me when the scope was
pointed at zenith (I'm 5'11"). In addition, the mirror box is heavy
at perhaps near 80 lbs. This combined with the awkward dimensions
make it barely manageable for short walks. Fortunately, the mirror
and cell can easily be extracted from the mirror box, shaving about 40
pounds off the weight. It's a full thickness mirror.

I took the scope out to Grady Park here in Houston, TX. For those
familiar with Houston, it's a nice little park just off San Felipe
just east of the Marathon Oil Tower, between Chimney Rock and Sage. I
like this park because one can drive easily directly onto the grassy
area in the middle, even though technically it's probably not allowed.

The visibility was perhaps Mag 4, going by the fact that I could
barely make out Hercules's "keystone" asterism at zenith.

SETUP
Setting the scope up took a bit of time, mainly because it involved
gross collimation of the secondary, i.e. axial position and rotation.
This procedure was complicated by the fact that I neglected to bring
my tools with me, save the Allen wrenches, so I was unable to easily
lock down the position of the secondary. As a result, after I got the
mirrors aligned, by examining a star out-of-focus I found that I was
cutting off approximately 30% of the secondary. And there was nothing
I could do about it that night.

The trapezoidal trusses (four of them) bolt on quite easily to the
mirror box, and the secondary cage similarly bolts onto the trusses.
All bolts are captive and have large knobs for easy twisting by hand.
At this 1989 mm focal length, the truss tubes are quite lengthy and
flex somewhat. However, after sliding on the elastic light shroud
(which takes some time and a bit of effort, or maybe I just need some
practice), the trusses are tautly constrained and form a very solid
structure. The shroud also protects the mirror from anything falling
towards the scope.

The NSS electrical package is really quite a nice option, consisting
of a hefty battery, charger, and power supply sitting in the rocker
box. The power supply has five 12V power plugs, one of which is a
cigarette lighter plug. The package comes with a dew heater for the
secondary, using one of two wires that run up through a truss tube.
The other wire is available for an eyepiece dew heater, which is not
included.

Unfortunately, in the process of assembling the telescope, I made the
bonehead move of switching on the power supply without checking the
two dangling wires coming out of the truss tube. The plugs were
touching, and as soon as I switched on the power, I heard a pop and
the 5 amp blade-type fuse blew. Before I blew the fuse, though, I did
verify that the dual cooling fans on the mirror cell ran fine. They
were so quiet that I had to actually touch the fan to know that they
were running. These fans suck air up towards the mirror, so even with
a hand right next to them it's difficult to feel anything.

My scope also came with Argo Navis digital setting circles. The
controller comes with batteries, but earlier in the day I'd obtained a
DC power cord with cigarette lighter plug, so I'd removed the
batteries. Now with the power out, I was unable to test the Argo
Navis! So I'll review that some other night.

The focuser is a Starlight Instruments Feathertouch and is extremely
well-machined and precise. It includes a fine focus knob, which is
helpful for focal ratios less than f/7 or so. At f/5.4, I found
myself fiddling with the fine focus quite often.

For observing, I had a Starmaster StarStep Observing Chair to help me
look through the eyepiece. With the scope pointed at angles of about
45° or less, I was able to either stand on the ground or sit on the
StarStep. At higher angles, I had to use the StarStep in its step
configuration.

Balance of the scope was excellent, after I'd attached the velcro
weight pack that NSS gave me with the scope. With a Telrad and Nagler
31 mm up at the top, the scope held balance down to as low as 20°.
Movement in both azimuth and altitude axes was very smooth, with just
the right "stiction". Switching eyepieces had next to no effect on
the feel of the movement. Large scopes are simply more resistant to a
couple pounds of difference here and there.

Overall, the structure is well designed and solid. NSS has really
done their homework on it, integrating several useful features and
niceties.

OBSERVING
By the time I finally got set up, Jupiter was long gone, so I was
limited to double stars and DSOs. The scope is a double star monster.
 I think Bob Royce outdid himself on this mirror. I couldn't believe
my eyes when I was able to resolve the double Delta Cygni at only 90x.
 With my 8" f/6 Newt (also equipped with a Royce primary), 150x was
the best I ever managed. Splitting Antares was easy as pie at 165x,
despite being only about 20° above the horizon. I was shocked at how
far the secondary was from Antares' glare; even a rank novice would
have seen it right away. I switched to 90x and just saw a glimpse of
the greenish companion before the seeing suddenly got worse. With the
8", 200x was the lowest I could go and even then it had to be higher
up and it was only visible for a few seconds. This mirror simply
outclasses the 8". Physics dictates that the larger mirror should
have better resolution, but I wasn't prepared for such a difference.

Despite about 30% of my secondary being cut off from misalignment,
stars were *much* brighter here under Mag 4 skies than with the 8"
under Mag 6 skies. Vega was almost blinding. There were so many
stars visible in the field that my Sky Atlas 2000 2nd Edition Deluxe
was completely inadequate to get around with, with its Mag 8.5 cutoff.
 This was compounded by the 1989 mm focal length, limiting me to about
a 1.3° FOV at my lowest power of 64x. This wouldn't have been a big
deal except that I only had a Telrad, which is next to useless in the
city. I got lost several times and my starhops were painfully slow.
It was pretty annoying. I need to get a good finderscope pronto. I'm
looking into a Lumicon 80 mm RA unit, but I haven't made up my mind
yet.

I did try a couple DSOs and I was surprised by how dim they were even
with the larger scope. No wonder I gave up observing deep sky in the
city. This only confirms that a lot of extended objects just
disappear in heavy light pollution, no matter what aperture you throw
at them. M56 was completely invisible, M57 a faint smoke ring. M13
was resolved fairly well but still very washed out. I quickly gave up
on the DSOs.

I did spend a few moments on the Moon. At close to full, it was too
blinding and uncomfortable to observe. I had a neutral density filter
at hand but it was almost 2:00 and I was tired.

I look forward to many more sessions with this wonderful scope! I
don't think I'll be using the 8" much more, since the 14.5" doesn't
require much more time to deploy. I can't say that about effort,
unfortunately. That mirror box is a beast to deal with. The scope
did come with wheelbarrow handles with wheels. Next time I might try
actually using them, it should make my life a bit easier. ;-)

Cheers,
Ritesh

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