NGC6888 the Crescent nebula

[RobertM]

Took this last night, I think it's certainly one of my best images to date, everything worked and no guiding - yippee.

Taken with Sky 90 operating at approx f/3 and the SXV-H9 unbinned.

20 x 300s unguided no flats, bias or darks.  Have the RGB component to process but I think I need more subs to get that bit right.

Details here: http://gallery.orpington-astronomy.org.uk/displayimage-558.html

[JohnP]

Hi Robert - very nice - lots of nebulosity showing as well - also very nice FOV. Looks like stars are slightly mishapen but considering you weren't guiding it's very good...

That H9 is a great camera - John

[MarkS]

Robert,

Lovely image.  Did I read that right - "no guiding"?  What, 5 minutes no guiding? 

F3 is really impresssive as well!!   

There's some wonderful nebulosity there, away from the main Crescent.  Well done. 

I look forward to more of the same - especially some RGB ...

Mark

[Fay]

Robert, I can't believe it is unguided, amazing, great image!!!!

[RobertM]

Thanks for the kind comments.

Looks like stars are slightly mishapen

John, It wasn't tracking that was the problem.  The issue was that there's a slight misalignment in polar alignment and the image train as you can see in the bottom right - at f/3 everything has to be exactly in line.  That also made focusing a pig so I need a 10-1 reducer !  The RGB channels will have to be redone as the Astronomiks are not all exactly parfocal with the Ha as I found out when I looked last night   It's my first image with this combination but will have to be more careful in future

Mark, yes no guiding and it'll be my setup for DSC together with the Canon.  There were two limits constraining me to 5 minutes - polar alignment was with the PA scope and needs tweeking and any longer than 5 minutes would have saturated stars.  Amazingly the crescent shape showed on the 5 second 2x2 focussing subs.  Don't forget it's only at an effective focal length of 180mm which doesn't put too much emphasis on tracking.

[JohnP]

So how did you polar align - was it just with the polar scope or have you got some other technique? I'm still gobsmacked when I look at this.....

John

[RobertM]

Alignment was with the inbuilt polar scope, I did try using the drift method but it didn't work for me so I need to practice.  Maybe someone could enlighten me at DSC.

[Rocket Pooch]

That looks quite good to me, but I would agree with John on the guiding.  Robert if you have a web cam and K3CCD or Guidemaster I can show you how to drift align with the web cam, its easy and takes about 10-15 minutes or so.

Chris

[Daniel]

Wow, that's an awesome image, Great for a guided shot, incredible for unguided, was the alignment just using the Kochab clock method through the polar scope? I've just got a new polar scope for the CGE and even though it's flashier than the CG5 one, Im not getting on with it as well, It doesn't have circles but has a place to put polaris and a place for a second star, tried it last night instead of Kochab clock method and ended up quite mis-aligned

[MarkS]

To get no trailing on a 5min exposure at 180mm you only need to PA to an accuracy of 5arcmin.  That's feasible with a properly set up PA scope.

[Rocket Pooch]

I thought it was 4.88 ArcSec per pixel for the setup?

[Mike]

Why not guide?

[RobertM]

Thanks Chris.

Good question Mike.  I wanted to take a simple setup down to DSC and concentrate on widefield, the C9.25 is a bit ott as a guide scope and I was sure I could get away without one. The PE on my mount should be less than one pixel at this resolution so it is in theory possible.

[Mike]

I will be bringing my ED80, ST80 and WO ZS66. WHichever one I am not using you are welcome to borrow at DSC to use as a guidescope. For widefield work even the ZS66 will make a good guidescope. You'll need a dual bar or rings of course.

[JohnP]

Mike - Have you got your mount back together yet? John

[Daniel]

If I get down to DSC this weekend, Im hoping to take the 120ED and the 80ED to guide with, would love to see what i can achieve in a  propely dark site

[RobertM]

Thanks for the offer Mike, I have a spare bar and rings so might take you up on that.

Chris, yes it is roughly 4.9 arcsec/pixel.

[Mike]

Mike - Have you got your mount back together yet? John

Yes it went back together for last DSC but its a bit rough with naff PE, mainly because the bearings were whacked around a bit too much with it being stiff first time around during disassembly and are probably a bit eggy shaped. Getting a new set of bearings is on my 'to do' list, but I haven't got around to doing it yet. I should get it done ASAP as they don't cost much and the nights are starting to darken now and I want to start getting back into imaging seriously and also using my VC200L a lot more which only the EQ6 can cope with.

I'll probably just bring the H-EQ5 and do widefield stuff this weekend like Robert. Theres not a great deal of good targets to image at this time of year, plus it doesn't get truly dark yet. The impending weather is probably not going to be good enough for anything serious this weekend anyway.

[Carole]

The impending weather is probably not going to be good enough for anything serious this weekend anyway.

Yes it's annoying isn't it with all the nice evenings we have had recently.
Even more annoying is they have all been on evenings when I had something on and couldn't get out there!!!!!

If I get down to DSC this weekend

Daniel if you do get to DSC can you introduce yourself as I don't think I've met you yet even though we've "spoken" a number of times on the forum.

Carole

[Mike]

....they have all been on evenings when I had something on and couldn't get out there!!!!!....

That is just about every night with me lately! I rarely get the chance to get out and image as much as I used to.

[Rocket Pooch]

I'll probably just bring the H-EQ5 and do widefield stuff this weekend like Robert. Theres not a great deal of good targets to image at this time of year, plus it doesn't get truly dark yet. The impending weather is probably not going to be good enough for anything serious this weekend anyway.

Wow you sound like a man who has given up imaging, there's 3 hours darkness and perfect for HaO3SII, also Cygnus is cool and has loads of stuff, not forgetting M13, LRGB will only take an hour!

[Mike]

Yeah agreed but compared to winter the list of possible options is pretty limited. I'm still prepared to do some imaging weather permitting !! Weather not permitting I have plenty of cider.

[Rocket Pooch]

I also have plenty of wine and beer, cunning eh!

[RobertM]

One way or the other it sounds like you two have DSC well sorted !

[Rocket Pooch]

Look drink is a last resourt, I really do want to use the SXD in anger this weekend to see if its 100% before I drag it to France.

[RobertM]

I've just reprocessed this as I found I'd set the black level too high in MaximDL.  I think it shows all the nebulosity now:

Original posting:



After reseting the black level and next to no processing in PS:

[JohnP]

Nice one Robert - that shows up the neb a lot better. The whole area is bathed in tons of nebulosity - look at this ultra widefield of same area posted on UKAI by Eddie Davies:

http://www.siamesedream.co.uk/ukai/2008/06June/art11002/ngc6888_large.jpg

Cheers,  John

[Fay]

Fantastic image, Robert. What were the imaging details?

[Daniel]

Wow, i really need to try that, I did a crescent a few weeks ago which came out ok, but needs a lot more subs, but that ribbon around it would be amazing to get

[RobertM]

Fay, it was with the Sky90 operating at approx f/4.5 and the SXV-H9 unbinned.

20 x 300s Astronomik 13nm Ha unguided no flats, bias or darks.

Sigma SD combined and DDP in MaximDL.  Loaded via FITS liberator with log stretch into PS then a very small amount of unsharp mask, 0.2 Gaussian blur and very mild levels/curves adjustment.  Could have done with a tad more in curve but not much.

[Rick]

Both of those images are in the gallery:

http://gallery.orpington-astronomy.org.uk/displayimage-558.html

http://gallery.orpington-astronomy.org.uk/displayimage-567.html

[MarkS]

Lovely image Robert - one of the best I've seen of the Crescent.  I definitely prefer the 2nd image because of the nebulosity.

I tried the Crescent myself on the Saturday night at DSC but the guiding was bad because my guidescope became dewed up.
Dew was a HUGE problem that night ...

[RobertM]

Thanks for the kind comments.  I need to redo it now the collimation is sorted so that all the stars are sharp ... if we ever get another clear night that is !

[Mike]

Great image Robert. Nice to see you reprocessed and made the background lighter. I hate seeing images with jet black backgrounds.