Sunday, 22 November 2020

Dither Fish

 Dither Fish

Recently I took the opportunity to take advantage of around 4 hours of clear sky here in Herefordshire.  I didn't have much planning time, so I opted to revisit a target I first imaged back in December 2019.  This was back when I just started using my Altair Quadband filter and I was sticking religiously to a tried and tested processing workflow in PixInsight.  As well as learning a bit more about the filter and processing, there has also been one other big step forwards with my data collection.  In my last few outings, I have started using the dither feature in SharpCap pro.  In my traditional way of imaging using SharpCap, I couldn't dither as the feature is only available when using the Live Stack feature.  However, I read that you could get around this by simply saving each of the subframes by clicking on a tick box in the Live Stack feature.  This sorted the sub frame saving issue which meant that I could then utilise dither when guiding.  I'll post more on the technique and settings I use another time, but for now, let's take a look at the results.
The two images below are cropped around the main part of the target showing a good proportion of the nebula itself, but also so well defined background.


The first image is quite noisy throughout the colour and background.  You can also just about make out that there seems to be a pattern where the noise appears to run diagonally top left to bottom right down the image.


The second image is part of my most recent image.  It shows the same cropped area, but notice the significant reduction in noise between the images.  While this is undoubtedly partly down to improved processing, the use of drizzling during the data gathering phase has made a huge difference, completely removing the diagonal noise patterns throughout the image.

IC1795 - The Fish Head Nebula

Having taken that big step forward and produced notable improvements, I shall undoubtedly dither on all my deep sky imaging from now on.  This only leaves me one thing left, and that's to show off the finished final image.  I seem to have a little problem with sensor noise coming through on the right side of the image.  A new dark library would of probably sorted that out.  Nevertheless, I'm still very pleased with this dithered quiet fish head.



Tuesday, 17 November 2020

Autumnal Trio - M57, M53 and NGC 6888

 Autumnal Trio - M57, M53 and NGC 6888

Back in September, we had a run of poor weather which meant I had the chance to revisit some old data and apply some new processing techniques.  Though astrophotography in my opinion is always going to be a case of continual refinement, it's been nice to get the chance to collect some new data.  Generally speaking, weather conditions have been a bit rough, so I haven't been able to do as much as I would like to do and it's just been a case of grabbing any opportunity I can without much in the way of thought or planning.  I've also come across a few bugs in my set up which has lead to a bit of frustration, knowing that time has been precious but needing to sort out these issues before I could proceed resulting in bit of a change in the way things are connected in observatory.  More on that later.  

M57 - The Ring Nebula

The first of the images I've had chance to put together is of this Autumn classic, the planetary nebula M57.  It's in the constellation of Lyra and during late Summer into early Autumn, can be found almost direct overhead as it gets dark.  While small, it is quite bright, so on this particular night in October, after addressing a few technical gremlins in the observatory and with cloud forecast, I couldn't spend hours and hours collecting data.  I was limited to around 90 minutes or so, but as you can see, that was more than enough to get some good data and colour using the Altair 183c Hypercam.  Through the eyepiece of a telescope, this target can easily be missed, not because it is that dim, but more often because it a quite small.  At higher magnification, you do lose a bit of brightness, but the ring can be resolved.  With the use of a UHC filter to help darken the background sky, the nebula can really be pulled out from it surroundings, but it will still only be visible as a wispy grey ring.  It's still though, an absolute favourite target for my observing list at this time of year.

M57 - The Ring Nebula in the constellation of Lyra.

  M33 - The Triangulum Galaxy

Given the choice of galaxies to image at this time of year, M33 has got to be one of my favourites ahead of some of the more traditional and well known galaxies of Andromeda and the Fireworks galaxy.  It frames well, responds very well to OSC imaging cameras and is well positioned throughout the night.  As is the case with most targets, the more data that is collected, the better.  This time around, again battling against deteriorating conditions, I was fortunate to get around 2.5 hours of data on it.  I wanted more.  I wanted way more, but cloud and bonfire night got in the way.  It wasn't until post processing did I really appreciate how much the sky quality decreased through the evening as more moisture condensed in the atmosphere combined with air pollution from fireworks and bonfires.  In the end, much of the data towards the end of the imaging was useless so I had to bin it.  Nevertheless, playing more with some new to me techniques of processing in PixInsight, I was able to pull out a pleasing amount of colour and data from the subframes I had collected.
Compared to my last effort, It's good to see that in my opinion, my imaging and processing skills seem to have improved somewhat.

M33 - The Triangulum Galaxy

NGC 6888 - The Crescent Nebula

This is a fascinating nebula.  NGC 6888 is found in the constellation of Cygnus, and it is one of those nebulae which when observing, often gets overlooked as it's tricky to pick out unless you're using some sort of massive light bucket and filter.  Imaging wise though, it's a different story.  Capturing a reasonable amount of data for the image is fairly straight forwards.  However, this truly is an example of more data the better the image.  The initial shape of the crescent is the first part of the nebula to be revealed.  However, I don't think OSC imaging really does this target justice.  To really bring the full extent of the nebula structure would mean adopting mono imaging techniques with filters and perhaps putting hours and hours of time into each channel.  What amazes me is that this nebula was first discovered back in 1792 by William Herschel using the equipment of the day.  Though he would of had far less light pollution to deal with (one assumes), he would of been using inferior quality optics, small aperture and no filters.
This data was obtained on November 6th. Unfortunately, the bonfire night antics this year seemed to spill over into a 2nd, 3rd, 4th and even a 5th night.  I knew I needed as much data as I could to help bring out more of the structure within the crescent shape, so in the creation of this image, I did include some poor quality sub frames which I would of otherwise ditched.  One day, I would love the opportunity to collect perhaps 6+ hours of data, but this time I've made do with around 2.5 hours or so.

NGC 6888 - Crescent Nebula

Bugs and Gremlins

For some reason following on from Summer, I have had a couple of issues with frames being dropped from the camera while imaging.  Since buying my quadband filter, I've been trying to adapt my imaging techniques to make the best I can of the filter.  Some of these changes have included using SharpCap smart histogram to analyse the optimum camera settings for me to use.  What's become evident to me is that I needed to increase my exposure time from 2 or 3 minutes up to around 10 minutes, if SharpCap is to be believed.  I've tried to adopt these new settings, but I noticed not all the sub frames were consistently being written back to the NUC PC in the observatory.  Now, there are a plethora of reasons why this might be the case.  The Hypercam I have is one of the earliest versions, so it has no on board memory for buffering.  But theoretically, given that it's been working predominantly fine, I can't think of a reason why this should be the root cause this time.  Secondly, it's a USB3 camera plugged into a USB3 port on the NUC PC and it's commonly advised by Altair, that the length of the USB3 camera used is kept to a minimum.  I use the cable supplied with the camera, so that shouldn't be causing the issue either.
Considering these requirements, I was left with two easy options to try.  I had a bit of a change around on the observatory pier.  Originally, I had 2 3 pin power sockets, the NUC and it's power supply and the all the associated cables coming from from the mount, cameras and controller all contained within one plastic weatherproof box mounted on the pier.  I wanted to change the USB3 port the Hypercam was plugged into on the NUC which needed a reworking of the cabling.  To help make room, and potentially remove some strain off the cables and ports, I took out the 2 3 pin sockets and put them elsewhere on the pier.  The other thing I did was to remove a connection to a spare USB2 hub which I also had on the mount.  Strictly speaking, I don't need this, but it makes life a bit easier when it comes to transferring data to USB stick at the end of an imaging run. 
The second thing I have applied is a simple driver update.  I noticed during my checks that the driver I was using for the camera was from early 2018.  Usually, manufacturers will update drivers as time goes on, especially if they still use those same drivers for their most recent products.  I couldn't get the camera drivers from Altair on their own, but they do come bundled with their imaging software, AltairCapture.  So, I downloaded the latest version of the software and updated my installed version.  I was pleased to see that the driver was also updated with a 2020 version.  In some initial testing when taking some dark calibration frames, it was good to see that only a single frame was dropped right at the start of the run.  This is often the case though as I will make last minute tweaks to camera settings while the first from is being captured.
Hopefully this work has got rid of the bugs and gremlins which have appeared.  Alas though, I will need some clear nights to get everything up and running.