Thoughts on my 10" Dob after a trip to dark skies in the Southern Highlands

[darkskybondi]

Hi everyone!

Visited a friend overnight in a beautiful little town in the Southern Highlands in NSW. This is the first time I've visited her and it gave me the opportunity to try my 10" truss dob out for only the second time in dark skies. I'm posting this in "equipment" because that's mostly what this post concerns!

Before I mention the equipment stuff, I'll just mention the dark skies thing. The moon was, of course, up last night and I don't ever recall being so anxious for that damn (gorgeous) rock to set. My friend didn't wait up - craters and moon-washed views of Orion didn't impress - but after the moon was well below the horizon, the skies began to glow for me. Amazing. Possibly darker than Bargo. If there was a light bowl from Wollongong or Campbelltown or Sydney, I couldn't see it. I sat there till almost 4am, spoilt for targets, behind this lovely house, listening to Radio National (Bush Telegraph, would you believe) on the laptop, with the horses hanging out in the property's paddock and the kelpie barking occasionally at the radio and the red light. A long way from Bondi, let me tell you. LMC and SMC suddenly emerged from the moonglow around 1.30, and the Milky Way just seemed to get brighter and brighter. Despite all the apparent targets, I kept being drawn back to the glow of Carina, and particularly the Carina nebula which, towards 3.30am, was simply spectacular at 120x. 47 Tuc is a very nice little (big) object too, that cheeky little glob.

Two days ago I observed M104 (Sombrero) from light-polluted Sydney skies from which I could make out the dust lane with averted vision. I thought this was very cool and looked forward to checking it out from dark skies. Well, it was nice last night too but still very faint for a Messier in dark skies (I'd have thought...) - I'm so new at this that I'd like your objective thoughts on the matter! I then searched for galaxies in Virgo for 45 mins or so, but found only one very faint thing with scant detail. Again, I would have thought that objects like M86 and M87 and all the rest of them would be easy to spot from inky black skies. (Omega Centauri, 47 Tuc and Tarantula were all nice too but surprisingly much less bright at the eyepiece than I expected for such dark skies. But perhaps you have to help me adjust my expectations of what 10 inches can do.)

And this brings me to the 10" SW truss. I've only just decided to write about my neurotic concerns about the thing since a friend came over a few days ago (one of about 5 so far who I've quietly introduced to the sky for IYA2009) and commented on how dusty the primary mirror looked when I shone a torch at it. Yes, yes, I know - probably paranoia, right? But I'm going to make you shudder when I tell you that I took a tissue to the secondary and cleared up a patch of it and it did look somewhat better. But I'm not sure whether it's dust on the primary or a sort of intrinsic graininess in the mirror. So is it a flaw in the mirror, or is it worth cleaning my primary (not with a tissue)? Perhaps graininess is an artefact of all mirrors? In other words, is it a flaw, or my paranoia, dust, or a mixture of all three? :shrug:

The only other concern I have is the stickiness of the truss rods. Those of you with a skywatcher truss may be able to help me with this. I loosened the small black hex screws as well as the big silver nuts and the movement of the truss was still not smooth. Should I be concerned? A flaw or my paranoia?

I hope you can forgive my newbie neurosis. I am having a wonderful time regardless of these small challenges and am looking forward to my first eyepiece purchase!

Have a great weekend :)
- DSB

[renormalised]

Even from the Sth Highlands, though the sky might look impressively dark, it's not as dark as you may think. Actually, even from the darkest areas, the best time to be observing and when it's the darkest is between 10pm and 2am. The reason for this is the Sun is at the opposite end of the planet around this time so you have the whole of the Earth and it's shadow keeping the light away. Earlier and later on, even though it's hard to believe just by looking, the sunlight is actually starting to creep across into the sky and brightening it ever so slowly. Then if you have moonglow as well, zodiacal light (that's light shining off dust in the plane of the earth's orbit), and a faint glow from the cities in the distance...well you don't truly have a dark sky.

You'll know a truly dark sky when you get to see one:)

It's that dark the sky looks like it's shining and it has a deeeeeep 3D effect to it when you look at it. It's almost like you can see the stars at their distances from Earth. It's a weird feeling, especially if you lay on the ground and just look out into space. You can very quickly become dissociated from where you are and it feels like you're actually floating in space. If you're not ready for it, it can really throw you into a spin. If Venus is up in a sky like that, it can be a bit of a pain as it's too bright. Can actually cast shadows. But you'll never forget a sky like that. It's a real treat to be able to see 11-12 of the Pleiades, M31 looks like a long thin mist, the Magellanic Clouds are awesome to see and if you know where to look and they're up at the time, both Uranus and Neptune are much easier to see....little blue-green dots:)

I've been to a few places like that....it's a privilege to have been able to see the sky like that. Very few people get to do so.

[darkskybondi]

This is cool advice renormalised. Thanks! :) I take it these could be a factor in the diminished brightness of objects in a sky that appears dark but isn't truly. Particularly faint objects like galaxies, and even nebulae like Tarantula. I suppose I was observing slighly after a waxing gibbous moon, so as you said, that has an effect, as do the other factors you mentioned. I can't wait till i get to experience a truly dark sky. There may be some opportunities in a couple of months for it! Can't wait to see Uranus and Neptune. I'm hoping to see the comet in a couple of weeks too, which would be a treat.

Meanwhile, do you have any suggestions about the equipment questions I had? I shall post photos if you like... :)

I've never seen a planetary neb yet either... any obvious suggestions for my next outing next new moon?

Kind regards
DSB :)

[glenc]

Some Planetary Nebulae: NGC 2392, 2438 in M46, 2440
http://www.iceinspace.com.au/forum/showthread.php?t=37536

[Starkler]

Just a thought. If the sky looks "inky black" it could be a sign that your eyes are not properly dark adapted. Try leaving the laptop at home.

[renormalised]

I've been thinking....I wonder what it's like for some of the animals that have far better night vision than we do, just what it's like to look up at the sky. Especially critters like owls....with their sensitivity, the night sky must look almost painfully bright with stars. Wonder how far down they can see. It'd be a few more mag' than we can, for sure.

[renormalised]

A truly dark sky has a very, very deep dark blue colour that doesn't look washed out. If it is "ink black", as Geoff said, your eyes still have to dark adapt. That's where the "shining" part comes into it....the sky looks like it's glowing because of the absence of extraneous light. The only light comes from the stars. I've heard that some people have mistaken the light coming from the band of the Milky Way when it's low to the horizon as being the twilight just before sunrise...I can see why. It's very bright on nights like this.

[JethroB76]

thats what I was about to suggest

[Quark]

High DSB,

Glad you are enjoying the delights of the southern night sky.

A good gauge as to just how good the seeing is would be to check what the lowest magnitude star is that you can see.

The Herald Bobroff Astro Atlas has a set of maps that show the stellar mag's for the whole sky. There are also some desk top planetariums that allow you to print out your own star charts showing the stellar magnitudes, Red Shift being one.

Using such charts check out a small region around the zenith or a region you are familiar with that has a suitable star field. About now the belt region in Orion works well. Use averted vision and see how dim a star you can detect from your chart.

Out here in the far west of NSW, on a Moonless night, the Milky Way throws a shadow. That is, it's glow is such that you, your telescope and the bushes around you throw a shadow.

Also, another very good gauge of how good the seeing is, is to note how close to the horizon you can look, with the naked eye, before the stars start to twinkle. Out here in the winter, often the stars are rock steady almost to the horizon.

Regarding your scope, if it is a truss do you have a light shroud?, if not get one.

Another tip, get one of those blue poly tarps, large enough to setup your scope on with maybe, a table to put your gear on and a couple of fold-up chairs. Use some tent pegs to hold it down. This has several advantages, if you drop something it will be on the tarp and you will be able to find it.

Also while walking around your scope, you and your guests will not be stirring up dust that may end up on your optics.

When ever you are not looking through an eyepiece make sure the caps are on the eyepiece. Did your scope come with a plastic cover that fits over the primary mirror such as comes with the Lightbridge and GSO Bintel strut dobs. If so use it.

The mirrors in your scope reflect light to the optical elements in your eyepiece. It is at the eyepiece that the image is focused. There can appear to be a lot of dust etc on the primary mirror of a scope, but it will still produce nice images.

To actually physically touch the surface of your secondary or primary is akin to an act of heresy. Next time you get this urge go and mow the lawn, wash the car and do some gardening until the urge passes.

If you are indeed determined to clean your mirrors then I would highly recommend you check out the excellent article on washing mirrors in the Articles section of IIS. On this subject let me say that I recently weakened and washed my 16" primary mirror for the first time in 14 years, my secondary is not yet dirty enough to clean. If your scope is new and you are looking after it, it is highly unlikely that it needs cleaning.

A 10" scope is a great instrument, my first scope was 10", you should get stunning views of The Key Hole Neb in Carina with about 16mm - 18mm eyepiece. If you have an eyepiece around 20mm - 25mm and screw in a OIII or possibly a broad band nebula filter the nebula will about double in size.

For 47 Tuc, Omega Cent and the Tarantula in the LMC my favorite view is with an old 14mm series 4000 Meade Ultrawide. Occasionally these can be picked up second hand, fellow IISer Kevnool picked one up on the IIS for sale section last year. In my opinion this is the best eyepiece Meade have ever made.

Just some thoughts.
Regards
Trevor

[gary]

Hi DSB,

Remember what the front cover of the "Hitchhikers Guide to the Galaxy" reads -
"DON'T PANIC".

Many a scope owner has been made paranoid by shining a torch on their primary. :eyepop:

Based on your description and the model of the scope, I gather this scope
is almost brand new, right?

Chances are, unless you have been out a few nights in a dust storm like this
one - http://www.iceinspace.com.au/forum/showpost.php?p=406875&postcount=1
that dust is unlikely to be a serious issue in this instance. :)

Unlike lenses on your camera, the primary mirrors don't need to always be spotless.

When you shine a torch on a mirror, things always tend to look worse
than they often really are. Though dust can deteriorate the brightness of
objects, the general wisdom is that you can often tolerate quite a bit
of dust on the primary until it impacts upon the optical performance to the
point it warrants a wash.

Part of this wisdom also comes from the fact that each time you have
reason to handle the primary mirror, the probability of damaging it by way of
an accident when handling it increases. That doesn't mean you shouldn't
ever wash the mirror, it just means you might only need to do it once
or twice a year depending upon your environment.

In your dialogue, I note that not once does the 'C' word appear.
'C' of course, stands for collimation and correct collimation tends
to improve the visual performance of newly purchased optics more than
just about any other corrective action. Collimating your scope,
particularly if you have transported it, should be simply a part of the
routine each night before you being observing.

If you want to test the optical performance of your scope, consider
performing some star tests like those outlined in the book by Suiter
See http://www.willbell.com/TM/tm5.htm
A quick Google will also reveal plenty of independent star testing tutorials.

Keep that tissue in your pocket and use a blower brush to clean off the
dust on the secondary.

Did your scope come with any 2" eyepieces? Some good 2" eyepieces are the
best thing one can add to any new scope.

Finally, when a scope is correctly collimated and in a dark sky location and
has been given time to cool down, atmospheric transparency and 'seeing' (turbulence)
tend to be the limiting factors when observing. There are many a time when
you can arrive at a dark sky site initially excited by the prospect of a fabulous
nights observing only to be hampered by seeing and transparency.
You will quickly come to recognize those nights where conditions are
exceptional.

Techniques such as averted vision and 'integrating' some tenuous image in one's
mind's eye take practice.

So don't get paranoid about a little dust and rather than concentrating on
washing the mirror today, if you haven't done so already, learn to collimate. :thumbsup:

Enjoy!

Best Regards

Gary Kopff
Mt. Kuring-Gai

[Dave47tuc]

Many have responded to you sky comments. Sky needs to be moonless to appreciate deep sky objects. As for the mirrors :whistle:

But as for the truss pole movements. Put a little Mr sheen on a rag and polish the poles. Try not to adjust the black knobs as they help put the poles in place. If you have loosened them get them set right by doing them up just enough to hold the poles in place and yet be able to move the poles up and down. You tighten the silver nuts up when the poles are in the up position, loosen them when lowering the poles.

Good luck.

[TJD]

IVE BEEN TRYING TO WORK OUT WHAT THOSE NUTS DID BECAUSE THEY DONT SAY IN THE INSTRUCTIONS INFACT I GOT MY 12 DOB LAST THURSDAY AND I FOUND MORE INFO ON THE NET THEN IN THE INSTRUCTION. ANY THING ELSE I SHOULD KNOW ABOUT:help::)

[darkskybondi]

Sorry it has taken so long to reply guys. Thank you for your great responses.

I sure must have been exaggerating about those dark skies... they were near-dark (as I've learned from people more expert than I) but they weren't ultra-dark as I've heard described here. I have learned from you guys that the fact that the moon may still have been affecting the sky even at 3.30am could have something to do with that, as well as transparency and seeing which I am not experienced enough to judge.

I'll be taking on board your advice - particularly about getting some 2" eyepieces. Do they have an advantage over the smaller diameter eyepieces? Will they make a big difference in DSO observation? Really just learning about this stuff. I really should be posting in the beginner's forum (which I only discovered recently...!)

I have become pretty decent at collimating the scope rapidly. I guess I was just surprised at the relative dimness of even the faintest DSOs in a 10". Is that simply a case of adjusting expectations? Is it probably because I never had a smaller scope and therefore don't know how much more powerful a 10" is than, say, a 6"?

Either way - I can't wait for the next new moon!!!! Hopefully will have a new wide FOV eyepiece by then, too!

Kind regards
DSB

p.s.Dave47Tuc - I played with those black knobs and they seemed to make a difference, Still friction though. Surprising since the scope is barely a month old! Still think Mr Sheen is the answer?

[Dave47tuc]

Sure but spray some on a rag not on the scope:whistle:
Also car wax or polish will help. Just need to make those poles a bit slippery.
Just do those black knobs up enough so the ota moves up and down but locks in place in the up position. :)