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