New Catalogue New Image

Good afternoon to you.  Welcome to my latest blog post.  You've either stumbled across this by accident, or are a fellow astrophotographer trying to fumble your way through the hobby just like me!  I'm playing a bit of blog post catch up, hence this post only a day after my previous, although timewise they're a bit of time apart.  Anyway, enough of the babbling.

In my last post, I wrote about the need to have a bit of a shape up in the observatory.  Some basic and routine things had gone by the wayside resulting in my last image perhaps not being as good as I'd hoped it would be.  Off the back of that, I returned to the observatory and did all the things I needed to do, including checking and adjusting polar alignment, checking and adjusting focus, carrying out a fresh 2 star alignment (more on that in a moment) and then taking the time to produce a new library of fresh calibration frames that should now see me through the next month or so.

In all this process, I was reminded of an issue that I came across a year or two ago to do with star alignment.  For some reason, my mount will happily perform a 2 star alignment and the target star will generally appear pretty close to the field of view, if not in it, for stars one and two.  But, when it comes to slewing to a 3rd star for 3 star alignment, the scope slews and points way out.  I'm not talking 40 or 50 degrees.  Perhaps 10 or 15, which is still considerable.  I've been through and checked everything I can think of.  Location settings on the mount, time settings and time zone etc.  The more I think of it, the more it started happening after I did a firmware update.  Perhaps it's time to check for the latest firmware, and try again maybe.  Nevertheless, two star alignment seems to be perfectly adequate and combined with plate solving, hasn't given me any problems.

Back to the image.  Thumbing through one of my books, looking for something to image that I hadn't gone to before.  I come across a CED catalogue number.  I hadn't heard of that catalogue before, but according to the star atlas I was using, the target was of the right sort of size and magnitude that I could be happy with shooting.  So, I looked up the catalogue, and it sounds really quite interesting.  Firstly though, this isn't a catalogue of unique objects.  Many of the objects in this catalogue are already included in the IC, NGC and other popular lists.  Where it differs is that it's a catalogue of a specific type of object.  It was put together in 1946 by a Swedish astronomer called S Cederblad.  It's a collection of 330 emission nebulae, rich in HII which means that they should react well with OSC cameras combined with filters, depending on how bright the target is of course.

The object I targeted for this image is CED 214 in the constellation of Cepheus.  It also appears in the more familiar Sharpless catalogue as SH2-171.  This image is a result of just over 3 hours worth of total light frames, plus calibration frames on top.  I think it's come up well, and the work I did in the observatory along with the new calibration frames have done it justice.  Next thing on my list of things to do is finally understand how to deal with the bloated circles around the brightest of the stars.  This is something that plagues many of my images.  There must be some way of dealing with it.  I just need to find out how!

***STOP PRESS***

Not necessarily worthy of a whole post in it's own right, but I've spent a couple of hours looking at ways to deal with the halos around the brighter stars.  For a first attempt, I think it's turned out well.  I used the image above at the starting point for the extra steps and then extracted the stars from the image.  The extraction is clever enough to only take the brightest areas, leaving the halos on the background image.  I was then able to address each halo individually and effectively rub out the halo from around the star.  Then, it was just a question of recombining the two images to produce the version below.  It takes some time to get around them all, especially in an image like this which has many bright stars in it, but worth it I think.