Astrophotography – deep sky

Horse head and flame

I’ve been reading a lot recently about camera noise and recommended ISO settings for each particular camera for astronomy. The camera I’ve been using was said to perform best at ISO 1600 which I think in astronomy terms is actually quite high for a Dslr. So I decided to test this out on the 8th Feb and managed 74x1min exposures at ISO 1600. I was very pleased with the low noise, although the light pollution south of me (Tamworth, Birmingham) was very strong since the horse head is relatively low on the horizon. I’m pleased with the result, although I think with a bit more processing experience I could possibly improve the image???  I was trying out Pixinsight for a second time so I hope to improve over the coming months/years. Canon 6d+Idas d1+Takahashi fsq.

 

 

M46 and M47

There are a couple of very interesting open clusters in Puppis, not far from Sirius, for different reasons. I found that I had not imaged M47 before, probably because I thought it was a relatively uninteresting plain cluster. Not so! Here is an image of it from the window-sill from yesterday:

I thought at first that the star colours were chromatic aberration, but, in fact they are there in images on the www.. (See https://en.wikipedia.org/wiki/Messier_47). Very colourful!

M46 includes a planetary nebula (NGC2438) in the same field that is very unusual. I didn’t manage to see this one yesterday, but here is an image from 3 years ago,

An Unexpected Session…

I’ve been working a couple of hours away from home a lot recently and have become accustomed to driving home in what look like great conditions for a bit of star gazing only to arrive to clouds, rain etc…

The BBC weather page definitely wasn’t optimistic, but after dinner the skies were clear (if not especially transparent) and so I decided go for it. I thought in for a penny and set up the photography rig. Target number 1 was to try and get some images of M51, but on setting up I found that it was hiding behind a tree (all 160 billion solar masses of it!) so I looked for something a bit higher in the sky and decided to go for the Double Cluster:

The images is built from 10x 5min guided subs. I left the camera clicking away whilst I put the kids to bed, and by the time I was back  M51 had come out from its hiding place and I attempted the same exposure time. Unfortunately, with the temperature showing -3 in the back garden my camera batteries gave up quicker than usual and I only got 8 before it gave up the ghost. Enough for the results below, however:

M51 Whirlpool

Whilst the camera was working on M51 I got the Dob out for some visual observing. I spent a good few minutes on M42 (does anyone else do this every time they observe? I can’t get enough of this target) and then moved up to Alnitak where the sky was good enough for a hint of nebulosity where the flame nebula is. It then took me a while to find the Crab but I got it eventually before moving onto Andromeda and M110. I decided to go for some new (to me) targets and spent some time looking for M101. I definitely saw something in about the right place but not 100% sure so maybe something to have another go at. I decided to go up towards the zenith and see if I could find Kemble’s cascade, but really struggled to see the stars nearby and couldn’t locate it. It was about then that the camera failed so I got the spare battery out and decided to point the camera at Kemble’s Cascade instead. The first sub wasn’t quite aligned correctly (see below)  and when I tried to re-align the mount my tablet decided it had had enough of the cold as well (touchscreens don’t work well with frost on apparently) which left me unable to control the mount. I was getting properly cold by now, but at least I’d had a bit of an astro-fix….

Kemble's Cascade

PD camera musings

At the last meeting, I had several discussions with people as to whether you could see galaxy spiral arms “live” with the PD camera.

Here is a raw frame of M51 I did 3 years ago:

Although not that prominent, they are there. This was with a “Senseup” of 1024, that equates to a stack of 1024 1/50th second frames, giving a 20 second exposure. So it is “live” and refreshes every 20 seconds.

Below is a stack of 11 of these frames , processed in GIMP

See  http://www.thornett.net/Rosliston/Astrophotography/DSO.pdf for info. on how this was done.

It also seems you can’t get the PD camera any more. PD’s mods to the camera seem quite simple, so I did a search for the Huviron camera upon which the PD is based.

Here it is: http://www.huviron.com/?portfolio=sk-b141dm846&ckattempt=1

It is discontinued, unfortunately.

I had a quick search on other Huviron cameras that might use the Sony Superhad II chip and a senseup of 1024, but couldn’t find anything appropriate

 

Digital Astronomy – things to do when it is cloudy!

When using the PD camera you can get away with very short exposures, for example, I seldom use more than a total of 300-400 seconds. Compare this with the times used by Geoff, Damian, Rob, Ken etc! My mounts and drives simply aren’t accurate enough to go longer (Its still fun though!). When doing this, I use the noise reduction algorithms built into the camera. A consequence of this is that sometimes dark halos appear around bright stars, and this is particularly obvious when the stars are embedded in nebulosity as in the window-sill image of M42 I posted recently. I tend to regard this as a small price to pay for the relatively instant gratification I get from the PD! Anyway, it would be nice to reduce this effect, and while contemplating the cloud cover, I thought of a method (or “workflow” to use modern parlance) that might do this with GIMP.

So, here is the M42 original, followed by a “de-haloed” version. It hasn’t gone away, but the “haloing” is reduced. I might try this on some of my earlier images if the clouds persist!

Trapezium and M42 from the Window-sill – 05/01/2018

Having been impressed with David Geary’s sketch of the Trapezium with his 16″ dob showing the 6 stars, I thought I would see just what I could do with the 80mm from the window-sill. This arrangement is more suited to wide-field views,but I gave it a go. I used an OIII filter I got for a Christmas present as this has an incidental advantage for this sort of thing. Since the filter has a narrow pass band it effectively makes the view monochromatic and removes chromatic aberration from the £100 ‘scope at the cost of the colour. Here it is with some OIII detail at the centre of the nebula. Can only see 4 stars though. Mind you, David’s 16″from outside is a few stops faster than the 80mm!

I have in fact just about managed to image the 6 stars before, but from outside with the 8″ SCT – see https://roslistonastronomy.uk/dsos-from-last-night-29th-30th-dec

While in the area I couldn’t resist another go at M42, even though it is a bit hackneyed by now. It is in colour though! (And you can see the Trapezium!). It is a 4-image composite to avoid washing out the centre of the nebula.