#1  
Old 01-03-2008, 03:58 AM
你B
Its only a column of dust

你B is offline
 
Join Date: Aug 2007
Location: New Iceland
Posts: 761
Obs report 29/2 - 1/3

Alrighty, the presence of clear sky had me test driving my latest aquisition, the 12" truss dob. I'm slowly getting the hang of it.

The 12" dob has 4, count 'em 4 fans on the mirror cell but I don't have an AC power supply to run em with. So cooling naturally takes a hella long time. Before observing, I had to place paper shims between the mirror edge and a couple of the silicon blobs supporting it as I found that collimation was slipping as I moved the scope in altitude. Luckily my plan worked and collimation barely moves during the course of the night. As for the secondary, I *think* its collimated - I WANT CATSEYES!!! The scope I think has a little bit of astigmatism, not sure if that is a byproduct of thermals around the mirror, seeing, or maybe the secondary is pinched (it appears to be held in a sleeve similar to those of the GSO dobs).

Scope: 12" F4.6 truss dob and it's 50mm finder (or mini refractor)
Time: 11pm-2:30am
Seeing: 6/10
Transparency: 4/5
Dew: No
Temp: 10慢


Started off with M42. Very detailed at 108x, 6 trap stars easy at only 83x. The smaller nebula M43 directly to the north actually takes on the shape that is visible in photos.

Homunculus Nebula
The brighter loop is noticably uneven, with a tiny star visible tucked in right near Eta Carinae. One of the lateral jets was easy at mags up to 353x but any higher and the nebula grows too dim to make much of it. Best views are obtained with mags in the high 200's to low 300's.

Running CHicken Nebula
Easy, obvious and very large glow surrounding a chain of stars just SE of Lambda Centauri. At 64x with the UHC filter, the nebula took up the entire central half of the FOV.

GUM 39
Located NW of the running chicken, this is a fainter object, appearing as a large rectangular glow, barely discernable from the background sky.

Ced 122
Just southeast of the Coalsack lies this large, faint nebula. Brightest portions surround an imbedded dark nebula and appeared as a faint haze at 64x with the UHC.

At this point I felt that something was 'not right' with the scopes collimation, so I grabbed a flashlight, allen key and toyed with the secondary. The result - noticable improvement!

Next I began scouring the Eta Carinae region - with the 50mm finder. The finder actually has a 1.25" diagonal with interchangable eyepieces, meaning I can put my 6, 7.5, 9, 12, 15, 18 and 30mm plossls to good use
The finder gave a lovely star studded field with Eta Carinae and NGC 3532 in the same FOV with the 18mm plossl. Through the main scope, Eta Carinae was obviously breathtaking, just that huge expanse and those dark clouds within it plus several clusters make it a real treat!

Saturn
Holy crap - at one stage I could hold 272x with superb clarity! The crepe ring was too obvious, in bouts of good seeing I could trace the Cassini Division atleast halfway from the rings ansae to the point where the meet the globe. I increased mag to 353x, dare I say that during 1 single split second moment I got a perfectly sharp view!!!! I saw a number of brown cloud belts and maybe a bit of limb darkening. Very good views but the seeing deteriorated before long.

Ghost of Jupiter
Strong blue hue, large outer halo with very well defined eye structure and pinpoint central star at 442x. Really cool object to view, the structure is great and I just love that colour! The Ghost of jupiter showed up really well in the 50mm finder with an 18mm plossl in place. This finderscope is going to be very useful for centering objects at high power in the main scope, also great for widefield milkyway sweeps!

Sombrero Galaxy
The moon was well up by now but at 176x the Sombrero still looked good, with the dust lane clearly visible. Should be a corker at around 200x in moonless skies

Omega Centauri
OMG!!! Unbelievable carpet of tiny pinpricks at 442x, broken up by dark lanes and features here and there! What a sight The northern hemisphere folk don't know what they're missing!

Eight Burst Planetary
Very nice at 442x, a C-shaped ring surrounds the bright central star with an unevenly bright interior. Looks almost like what one sees in a photo, minus the techni-colour ofcourse! Also slammed the mag right up to 707x but that was just empty magnification. AN absolute pearler at 442x though.

NGC 3918
The Uranus look alike near Crux. Nice, greenish orb at 442x. I pumped the mag to 707x and dare I say the view was pretty good, same as at 442x only bigger, even with my probable crap collimation. I even suspected a bit of structure but i don't know - that's one to revisit.

ANd that concludes a fine night of observing I suspect this scope has killer optics - I just need a Catseye triplepack XL to make 'em dance! I might also replace the old, rusting spider/secondary assembly with a fresh product later on.

But yeah, I'm very happy with the performance of the 12", potential planet killer and mad views of deep sky
Reply With Quote
  #2  
Old 01-03-2008, 08:00 AM
goober's Avatar
goober (Doug)
No obs, raising Harrison

goober is offline
 
Join Date: Nov 2007
Location: Melbourne, Australia
Posts: 793
Great SAB - we overlapped last night. I could see some cloud down south and thought it may be over Berwick. I got some good seeing on Saturn at 270x - fantastic.

Hey, I'm about to post a sketch of Sirius in my report from last night. Can you check please it out and tell me if I got it or not? I'm not sure...
Reply With Quote
  #3  
Old 01-03-2008, 08:04 AM
luvmybourbon
only on weekends

luvmybourbon is offline
 
Join Date: Jan 2008
Location: pioneer bay. vic
Posts: 65
that made great reading. thanks
Reply With Quote
  #4  
Old 01-03-2008, 08:25 AM
Dennis
Dazzled by the Cosmos.

Dennis is offline
 
Join Date: May 2005
Location: Brisbane
Posts: 10,902
Nice report, it reads like you had a very enjoyable session. Do you record/write/type the details and your impressions as you go along, or do a memory dump at the end of the session?

Cheers

Dennis
Reply With Quote
  #5  
Old 01-03-2008, 11:24 AM
你B
Its only a column of dust

你B is offline
 
Join Date: Aug 2007
Location: New Iceland
Posts: 761
Quote:
Originally Posted by goober View Post
Great SAB - we overlapped last night. I could see some cloud down south and thought it may be over Berwick. I got some good seeing on Saturn at 270x - fantastic.

Hey, I'm about to post a sketch of Sirius in my report from last night. Can you check please it out and tell me if I got it or not? I'm not sure...
There was some cloud threatening to move in from the south east around midnight but incredibly it actually disappeared

Hopefully tonight the seeing will be just as good btw, I checked your Sirius sketch....
Reply With Quote
  #6  
Old 01-03-2008, 11:25 AM
你B
Its only a column of dust

你B is offline
 
Join Date: Aug 2007
Location: New Iceland
Posts: 761
Quote:
Originally Posted by Dennis View Post
Nice report, it reads like you had a very enjoyable session. Do you record/write/type the details and your impressions as you go along, or do a memory dump at the end of the session?

Cheers

Dennis
Yep I just jot down notes on a piece of paper, basically a quick description, mag used etc.
Reply With Quote
  #7  
Old 01-03-2008, 12:17 PM
Karlsson
Registered User

Karlsson is offline
 
Join Date: May 2007
Location: in exile in Doha, Qatar
Posts: 159
$AB - an excellent observation report - really enjoy reading them!

Quote:
Originally Posted by 你B View Post
The 12" dob has 4, count 'em 4 fans on the mirror cell but I don't have an AC power supply to run em with. So cooling naturally takes a hella long time. Before observing, I had to place paper shims between the mirror edge and a couple of the silicon blobs supporting it as I found that collimation was slipping as I moved the scope in altitude. Luckily my plan worked and collimation barely moves during the course of the night. As for the secondary, I *think* its collimated - I WANT CATSEYES!!! The scope I think has a little bit of astigmatism, not sure if that is a byproduct of thermals around the mirror, seeing, or maybe the secondary is pinched (it appears to be held in a sleeve similar to those of the GSO dobs).
Astigmatism is unlikely to be caused by tube currents or dodgy seeing. In theory it could be the result of uneven cooling, but since you did not use the fans that is not very likely either (that's the good news about sloooow cooling - much less chance of temperature gradients and deformation in the mirror itself )

Assuming the optics are basically fine, you may want to look into the paper shims you used - they would likely cause the mirror to be supported unevenly and thus cause an ever so slight saddle-like deformation that will show up as astigmatism. If it is serious enough, try to see whether the direction of the astigmatism correlates with where the bits of paper are - if you can live with it I'd leave it for now...
Reply With Quote
  #8  
Old 01-03-2008, 12:37 PM
你B
Its only a column of dust

你B is offline
 
Join Date: Aug 2007
Location: New Iceland
Posts: 761
I actually removed some of the shims, I dont know if it changed the situation. I'll continue to experiment. Might just leave one shim in there (which is necessary). The astigmatism isn't severe, stars are visibly oblong but not greatly so just inside and outside of focus.

The mirror itself is premium quality, so maybe it is those shims or it could be the fact that the secondary is housed in a sleeve.

Last edited by 你B; 01-03-2008 at 12:48 PM.
Reply With Quote
  #9  
Old 01-03-2008, 10:44 PM
ngcles's Avatar
ngcles
The Observologist

ngcles is offline
 
Join Date: Dec 2006
Location: Billimari, NSW Central West
Posts: 1,571
Hi 你B,

As usual an excellent write-up -- seems like you are having a great time with the new 12". But in the end, will 12" be enough? Hmmm ...

Take a good look at the collimaton of the secondary and also, centration of the primary under the secondary. Unless it is nicely centred under the secondary, it can occasionally give an astigmatic type appearance. Is the primary in a sling or in a cell like the 10" GSO?

你B wrote:

"I increased mag to 353x, dare I say that during 1 single split second moment I got a perfectly sharp view!!!! I saw a number of brown cloud belts and maybe a bit of limb darkening."

Isn't it just sensational when it snaps in like that?

I must have seen that happen dozens and dozens of times and yet it still amazes me and leaves me dumbstruck -- just for a moment. One such incident that comes to mind was a night 2 years ago out at my southern highlands spot where we observe every new-moon weekend. It was a night of very good to excellent seeing and when that happens, I tend to spend a lot of time on very small high-surface brightness objects like PNe. I remember that I spent a lot of time on NGC 2392 (Eskimo), NGC 3242 (Ghost of Jupiter) NGC 3132 (Eight-Burst) and IC 418 (Wow, Woooooww) at x317, x371 and even x494. On Saturn (somewhat lower in the north), the image at x317 was almost perfectly stable but x371 was a bit wobbly until that magic moment(s) arrived -- it was at x371 when it snapped in for about 3 seconds and it was sensationaly beautiful. One is tempted to describe it as "Hubble-like". I let out a yelp as it happened but the show was over before my observing comrades had realised what happened. There was swirly detail in the dark grey/fawn belt immediately adjacent to the eq band, Cassini looked like you could drive a bus through it, the Enke division was there and easy to see and the crepe ring stood out like a honeymooner's whatsername -- brown and dirty violet in colour. Certainly stand's out in the memory!

For interest's sake, reproduced is the observing note on NGC 2392 from that night:

x494 10'TF
NGC 2392 PK 197+17.1 PNG 197.8+17.3 Planetary Nebula
*RA: 07h 29m 11.0s Dec: +20 54' 39"
Mag: 9.9 (P) Size: 50.0" Class: 3b+3b
Mag C. Star: 10.5 R.V.: --- Source: Str-ESO

*Wow!! Words nearly fail. Virtually all of the detail in the Hubble image is visible or at least there are hints of it. This PNe has a prominent mag 11 central *. The Whole halo just over 1' diameter with a very diffuse looking edge. This outer halo comprises the outer 15" diameter and is patchy in brightness with a radially streaked appearance like someone has raked it outward in places. It is blue without filtration. Then heading inward there is a definite, fine circular, maybe slightly ovoid boundary where the inner halo takes over. The inner halo is generally smoother, but at times when the seeing settles you can occasionally make out a maze of fine weakly brighter streaks criss-crossing the centre -- particularly in the S half of the inner halo and some occasional tiny darker areas between. A magnificent object -- wonderful!

This is a link to the Hubble image:

http://antwrp.gsfc.nasa.gov/apod/ap031207.html

It's a pity we can't book and pay for seeing like that in advance!

Best,

Les D
Contributing Editor
AS&T
Reply With Quote
  #10  
Old 02-03-2008, 10:34 AM
PhilW's Avatar
PhilW
Registered User

PhilW is offline
 
Join Date: Mar 2007
Location: Melbourne
Posts: 283
Sab, could you post a picture or two of how the primary & secondary are supported?
Reply With Quote
  #11  
Old 02-03-2008, 12:19 PM
goober's Avatar
goober (Doug)
No obs, raising Harrison

goober is offline
 
Join Date: Nov 2007
Location: Melbourne, Australia
Posts: 793
Quote:
Originally Posted by ngcles View Post
...and the crepe ring stood out like a honeymooner's whatsername -- brown and dirty violet in colour.
I've spent a couple of minutes on this and can't work it out. I better move on
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 01:31 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Lunatico Astronomical
Advertisement
SkyWatcher Australia
Advertisement
OzScopes Authorised Dealer
Advertisement
Bintel
Advertisement
Meade Australia
Advertisement
Astromechanics
Advertisement
Celestron Australia
Advertisement
Astronomy and Electronics Centre
Advertisement