Re: First Light: 14.5" f/5.4 Newtonian

From: J. Jason Fry (jason_fry_at_interconnect.net)
Date: 07/05/04 

Date: Mon, 5 Jul 2004 12:46:43 -0500

Ritesh,
   I was interested to learn that Jim made you a structure with that slow a
focal ratio. His website indicates that he will make them only F/4.5 or
faster. In fact his 14.5" scope he normally makes is an F/4.3. I recently
bought a 16" F/4.5 (Pegasus mirror), but I was interested in F/5 to avoid
coma (I'm also 6'5" tall). I settled for the standard 16" scope Jim makes,
and I'm very happy with it. The focuser is at 72" or so when at zenith,
which is EXACTLY where my eyeball is flat-footed, so it's nice to not need
even a step with a 16" scope. But I didn't even know Jim would consider
making a structure that long. I'm wondering what the price difference was
from his listed structure prices. Also, I bet you paid big bucks for your
Royce mirror. I've seen on their website the prices. My Pegasus mirror by
John Hall (Carl Zambuto's mentor) is very primo - 1/19.5 P-V, and 1/52 RMS,
with a .986 Strehl. Does Royce provide comparable spec info?
    I have Argo Navis on my NSS also, although I just recently picked up the
DC power cable, and haven't had a chance to use it yet, although I hope to
later this week. I've used the batteries for all my observing, and the only
problem is they run out after a while. However, I used them for about three
nights or so at TSP before they ran out there, and then a couple of nights
in a row the next time (first until 3am and the second until dawn), and they
only ran out about half hour before dawn. BTW, there's no need to remove
them from your AN, in that the unit will use the DC cable if connected, and
then you can use your AA batteries as back up in case of what happened to
you. Just a thought.
    I live in south Texas in Kingsville, and we have an event called Deep
South Texas Stargaze near here with air conditioned bunk rooms, RV sites,
and very dark skies (7.1-7.5 mag). A lot of folks from all over TX and also
from Houston have come over - it's just half a day's drive. The 2005 date
will likely be Feb 9-13. Your new scope would love those dark skies! We
had some guys from that area who are part of JSC Astronomical Society and
they thought they were in heaven. Watch our website this fall
www.geocities.com/kingsville_astronomical_society/dsts.htm.

Jason Fry
Kingsville, TX

PS - What other eyepieces do you use other than the 31 Nagler?

"Axel" <ritesh_laud@hotmail.com> wrote in message
news:9ba65d5d.0407050053.2096bcf9@posting.google.com...
> 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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