The Wall at DSC

[MarkS]

The Wall in NGC 7000  - this time from DSC: 21 August 2009

20 x 5minute exposures.  Modified Canon EOS350D on Celestron C11 with F6.3 reducer and Astronomik CLS filter.
Stacked, 3x3 binned and lightly cropped in IRIS.  Mild deconvolution applied.

I'm not too happy with this but I'm posting it anyway - somehow I managed to get the collimation wrong - lots of coma on the left hand side.  However it is much smoother than the equivalent image taken in Sidcup:  http://forum.orpington-astronomy.org.uk/index.php?topic=4958.0
It's still very much a work in progress and I haven't properly corrrected the vignetting yet.

Preview below and full size (3x3 binned) here:  http://gallery.orpington-astronomy.org.uk/albums/userpics/10046/wall210809v1.jpg

[Daniel]

Mark, that's lovely, fantastically smooth and detailed, the coma you mention is very slight I'd be well chuffed with a result like that!

Daniel
:O)

[JohnP]

Mark consider you had totally dismantled your scope the day or so before I would say it's excellent - Looks great to me.

John

[Rocket Pooch]

I like it, but a Hyperstar would make all the difference

[Daniel]

hehe, I'd like to think that, but the hyoerstar would never match this resolution!

Daniel
:O)

[MarkS]

a Hyperstar would make all the difference

Aha, I have an alternative cunning plan. 

I've been doing lots of research and experiments recently.  I have also seen an example of an image produced by someone using a C8 with the Celestron focal reducer and it gives a very well corrected field larger than a 35mm square.  My suspicion is that the reducer has been designed as a perfect match for that particular scope and so it undercorrects for the C11.   In theory, each SCT scope in the range would need its own dedicated corrector but the decision taken by Celestron (& Meade) is to manufacture a single "universal" reducer.

My calculations indicate that it may be possible to correct for the residual field curvature by placing a lens of approx one dioptre (i.e. focal length 1000mm) right next to the CCD.  Because it is placed so close to the CCD the lens would not require high manufacturing tolerances - I'm thinking along the lines of cannibalising a pair of standard reading glasses.

Watch this space ...

[Fay]

Well, Mark, I would be very happy with that, interesting to see how your experiment works out

[RobertM]

Very good image Mark and a very cunning plan !  All you need now are reading glasses with circular lenses the right size.  I suspect you are right about the FR as it covers instruments from the C5 right up to C14.  Also don't forget it was designed at a time when imaging chips were relatively small so the sort of problem you see wouldn't have been an issue.  You could also consider the Alan Gee or Optec reducers as an alternative, I think Duncan has the Alan Gee unit so you could see how he gets on with his.

[MarkS]

I've already looked at Alan Gee Mk II.

I had a thread going on UKAI (http://ukastroimaging.co.uk/forums/index.php?topic=46305.0) so I won't repeat it here. 

I eventually concluded that on the C11 the Alan Gee can get a flatter field but, when doing so, I found the chromatic aberration to be too high.  Again, on other scopes, it may well work well.

There's a very interesting image here taken on the C8 with the standard Celestron reducer:  http://www.flickr.com/photos/26671216@N02/3570358231/  (look at the full 4096x4096 size)

Mark