Saturday, 15 September 2018

M57 - The Ring Nebula and Dealing With Hypercam Noise

M57 - The Ring Nebula, and the story behind the image.

Every image has a story.  Be it about the subject itself, the location or how the image was obtained.  This image represents for me 2 things.  Firstly, proof that not all astrophotography images are about full frame objects, or targets cropped within nanometres of their boarders.  An impressive planetary nebula nestled in amongst a field of view littered with stars, M57 is amongst the smallest targets out there to image, so getting any detail in it at all can take some effort.  Secondly though, the image has taught me a lesson.  One that I hope will now significantly improve all my future images taken with the Hypercam 183c.  More on that in a moment.
My last post set out the process I go through to collect the data for my images.  Whilst getting the screen shots for that post, I imaged M57 - The Ring Nebula.  I have now had the time to go through the steps of stacking and processing the data to produce the final image.  You see many images of this target because of it's apparent brightness, but more often than not, the images will be cropped or enlarged to see the Nebula in as much detail as possible.  Indeed, I have done this before myself.  This time however, I wanted to add a sense of scale to the image, so only cropped the image where absolutely necessary to remove the rough edges of the final image after the stacking process.

Almost lost in a myriad of stars, M57 is a popular visual target.
The details behind the image:-
  • 25 x 180sec light frames
  • 25 x 180sec dark frames
  • 31 x 90ms flat frames
  • Stacked and processed in PixInsight and GIMP
So, what of the one big learning aspect of this image in particular?  Well, I have already divulged that secret!  Ever since I started using the Hypercam, I have struggled with the anomaly of noise from the sensor encroaching the righe side of every image.  To be clear, this in itself is perfectly normal.  It is behaviour (though undesirable) of the Sony sensor used in the cameras, and it is found in every camera using that particular sensor chip.  Time after time, I have been told that correct use of calibration files (darks and flats) will get rid of the noise in the final stacked image.  To illustrate this noise, as well as the amp glow from the chip, here is a single 3 minutes sub frame, stretched, but not debayered.  Notice the amp glow across the top and bottom edges, but in particular the additional noise on the right edge which looks like some sort of extravagant starburst effect from a bright star just out of frame.

As more and more of these images are stacked up, the noise become more and more prevalent, and up until now, I have struggled to get rid of it during the stacking and calibration process.  This has meant that many of my images have been significantly cropped to cut out the noise.
I think I managed an imaging run once earlier this year where I successfully produce a stacked image without the noise on it, but I have failed to remember how I did it.
After much more thought and reading, I understood that the dark frames should be removing this sort of anomaly, so I started wondering if I just wasn't producing enough information in the master dark file to take care of this noise.  So, that left me with one option.  To increase the number of dark frames I was taking.  I have never found a definitive ratio for the number of light frames to dark frames to flat frames to obtain for each image.  Sometimes it has been 60 light frames and 20 darks.  Other times 20 light frames and 10 darks.  For this image in particular, I went with the approach that if I took one dark frame for every light frame, then I would be able to experiment by changing the ratio each time.  This is when I seemed to have struck gold.  
This is what the final stacked image looked like when PixInsight had finished the stacking process.  Remember that the image has had not been cropped at this point, has had no processing done to it, but has been stretched to show the detail available.

Notice that the noise and a majority of the amp glow has now been dealt with successfully, allowing me to make far better use of the whole frame, instead of cropping out any interference, and loosing about 1/3 of the image in the process.

So there you go, one image and 2 stories.  Now it's just a question of making sure that this is repeatable.  It all come down to the fact in this instance that I simply didn't have enough dark calibration frames.  All I need to do is get out there on the next clear night and repeat.
I hope this helps other owners of the Altair Hypercam 183c series of cameras.  I see it raised regularly in various forums and groups, but no-one as far as I can see has been able to say definitively what they do to combat the problems.
Thanks for reading, and clear skies! 

Thursday, 13 September 2018

Data Capture Workflow - Astrophotography and the Hypercam 183c

Altair Hypercam 183c Workflow

Hello!  After discussing with various people, the topic of how I go about preparing for and collecting my data for my images, I thought it would be useful to put together a workflow for others to consider using as a basis for their own imaging process.  I haven't gone into too much detail with settings in each of the steps.  These settings will be different for each person and each combination of kit, but it will be a good starting point.  So, before I proceed, this is a list of what I use for my own imaging.
  • SkyWatcher EQ6-R Pro mount.
  • Starwave 80 ED-R telescope.
  • Starwave 50mm guidescope.
  • GPCAM Mono guide camera.
  • Altair Hypercam 183c colour CMOS imaging camera.
  • Altair CCD light pollution filter.
  • LED artists tracing light board.
In terms of software, this is what I use.
  • Sharpcap Pro 3.1
  • Fits Liberator
  • Cartes du Ciel
  • PHD2

Polar Alignment

Every article I read about imaging and using an EQ mount always talks about polar alignment.  As I have found out, there are numerous ways of achieving polar alignment by using all sorts of different gadgets or software to aid the process.  The EQ6-R Pro comes with it's own polar scope, but as yet, I haven't used it.  Instead, I start off by ensuring my guide scope and main scope are aligned fairly well to true north, and the latitude is set correctly for my location (approximately 51.9 degrees north).  It doesn't have to be exact, but personally, I like to get things as accurate as I can.
My personal preference for achieving a good polar alignment is to use Sharpcap.  In Sharpcap Pro, there is an in built polar alignment tool which connects to your guide camera.  You need to have your mount aligned roughly to start off with, give or take 5 degrees or so.  Sharpcap can then plate solve the stars it sees through the guide camera and guide scope, before then giving you directions for adjusting your mount.  I took this screenshot showing what I saw during the process.

Polar alignment routine in Sharpcap Pro

3 Star Alignment

Once the mount is polar aligned, I go through the process of performing a 3 star alignment of the mount.  This process allows the mount to learn where given star are in the night sky, and can be incredibly accurate.  To carry out this alignment, I use an illuminated reticule in the telescope's eyepiece holder.  This reticule given me a crosshair target in the eyepiece meaning I can be sure that the stars used during the 3 Star Alignment routing are perfectly in the centre of the field of view.  
The alignment is carried out following prompts and instructions on the handset of the mount.  Once alignment is complete, the scope itself is ready to use, and it's time to move onto preparing the specific imaging hardware.

Fit and Focus the Hypercam

Once the scope is aligned, I remove the diagonal and reticule eyepiece, fit the 80mm extender, filter and camera and once again, return to Sharpcap.  The next part of my workflow is to get the Hypercam focussed as best I can.  I don't have a motorised auto focuser, so this is an important step that I need to get right first time.  If I need to make significant changes to the focus during the imaging run, I run the risk of making too much of a change and possibly stopping the latter process of stacking and image integration from running smoothly.
To achieve focus, in Sharpcap, I point the scope at a bright star, and then fit a bhatinov mask.  I used the zoom feature in Sharpcap and then turn the focus knob accordingly.  The idea is that the diffraction spikes caused by the mask are equally spaced when good focus is achieved.  The screenshot below shows the exposure time and gain used during the process of focusing, and the equally space diffraction spikes.

Equally spaced diffraction spikes showing good focus.

Choosing a Target

I am now ready to slew the telescope to a chosen target.  To do this, I used planetarium software called Cartes du Ciel.  I could just use the hand controller connected to the telescope, but for ease of use, I prefer the software.  For this particular night, I decided to image the Ring Nebula, or M57.  Once the mount is connected to the laptop and the software is launched, I can select a target and allow the mount to slew the telescope to the target.
M57 selected in Cartes du Ciel.

Framing the Target

Even the most accurate of go to mounts will still require the finest of adjustments if you plan on imaging a target.  This is especially important when imaging either very small, or very large targets.  You want to be sure that you fit as much of the target in the frame, and get it as central as possible.  To do this, I switch back to Sharpcap and adjust the exposure and gain settings to give me some sort of idea of where the target is.  M57 is actually quite bright, so it's fairly straight forward.  However, for dimmer targets, it can take a bit of time to get things framed accurately.  Sharpcap has a crosshair tool to help framing objects accurately.
In this screen shot, you can make out the shape of M57 near the centre of the crosshairs.  You can also see the scope controls available within Sharpcap which allow you to make fine adjustments to frame the target exactly how you want it.

Moving M57 into the centre of the frame using the crosshairs and mount controls in Sharpcap.

PHD2 - Guiding Calibration

So far, all the work has been done to get the mount slewing to targets as accurately as possible, and the target selected, framed and put into focus.  However, for prolonged exposures of more than around 60 seconds, it is necessary to run guiding software to improve the accuracy of the mount. In essence, guiding locks onto a star via the guide camera, tracks it as it moves through the sky and then issues adjustment commands to the mount to keep the guide star in the same location relative to the field of view.  
In PHD2, the guide camera is connected to the software, and as best practice, I use the Guiding Calibration feature in the software to 'teach' it how the mount is currently reacting to commands.  A guide star is selected and then commands are issued to move the star North, South, East and West during which time, PHD2 takes measurements of how much the mount has to move to move the star the required amount of steps.  The process is fully automated once started.  Once complete, guiding starts automatically.  If you want, you can leave it guiding from there.  However, I chose to perform some additional steps.
This screen shot shows the calibration steps being carried out.

PHD2 Calibration steps.

PHD2 - Guiding Assist

There are many settings in PHD2 which can be changed to try and improve performance.  To be perfectly honest, I don't understand most of them, but they all seem to be important.  So, to help me put the correct values in all these places, I use the Guiding Assist tool in PHD2.  Guiding Assist stops any guiding that is taking place and just measures the movement of the selected star.  From these measurements, the software can measure the increments in which guide commands need to be issued, and also if selected, the backlash of the mount.
Guiding Assist is left to run for around 2 minutes so it can make all the measurements it needs to.  Once completed, it then allows you to adopt the suggested settings and automatically enters them into the appropriate fields.
This screenshot shows the measurements that are taken and the different information it provides, and the second screenshot shows the results at the end of the process.  Remember that this changes from night to night and needs to be done every time everything is set up.

PHD2 Guiding Assist in progress.
PHD2 Guiding Assist results.
Once the settings have been adopted, PHD2 then starts guiding.  Before I carry on, I prefer to leave the guiding process run for a few minutes and watch the graph in the software,  Theoretically, the flatter the lines in the graph, the better guiding is working, and the better the mount is set up.

The difference in the graph shows the point when PHD2 Guide Assist stops taking measurements, and then starts guiding.

Starting the Imaging Run

At last, I'm ready to start turning my attention to capturing my images.  There are a final few calibration steps I carry out before starting the image capturing.  Back in the Sharpcap software, I have recently started making use of the Smart Histogram.  The feature analyses the sky conditions, and with some input from me about such things as how long I want the total exposure to come to, and the shortest and longest individual exposures I am willing to use.  For example, if I know I only have 3 hours total to spend, I can tell Smart Histogram that I want to collect 90 minutes worth of data in total.  Smart Histogram is then able to give me the optimum gain and exposure length to use for the parameters I set.  Again, this process can take a bit of time because Sharpcap actually takes a range of individual frames of differing lengths and gains to build up it's graph.  The remaining time left out of the 3 hours I can use to collect calibration frames for use during image processing.
This screenshot shows the histogram analysis in action.  Once the results are displayed, you can input them into Sharpcap ready to start the imaging run.

Smart Histogram calibration steps.

The Capture

Now it's time to start the data capture process.  The mount is set up, the software is configured, guiding is running and I now know the optimum settings to apply to the Hypercam in Sharpcap.  All I need to do is set the imaging run off within Sharcap.  I can set the imaging run to either take a fixed number of exposures, to run for a certain total amount of time, or take pre-configured numbers of exposures.  Using the information from the Smart Histogram tool, I usually know by this point how long or how many frames I need to take.  It's just a question of applying the settings and setting the process off.
Each frame is displayed in Sharpcap so you can see what's going on.  You can also see how much time is left in the run and how many frames have been taken.

Hypercam settings used for imaging M57
It's important to keep an eye on the PHD2 graph throughout the imaging run.  Normally, just keeping an eye on the graph is sufficient.  However, PHD2 does give an audio and visual alarm if it loses contact with the selected guide start because of cloud or dew.  To monitor this, I tend to have both the PHD2 window and the Sharpcap window open at the same time.

Monitoring the data capture of M52, and PHD2's guiding performance.

Capturing Dark Calibration Frames.

Once the main imaging run is complete, and all the light data is collected, my last job of the night is to collect the Dark calibration frames.  These are simply additional images taken using exactly the same parameters as the lights at the same focus and camera orientation.  The only difference is having the cap on the end of the telescope.
This screenshot is of Sharpcap taking the Dark calibration frames.

Collecting Dark Calibration frames.

Flats and Fits Liberator

This is usually the last task of the night.  The following morning, I will then take my flat images, but they can be done at anytime providing the focus and camera orientation are maintained throughout.  This is really important, so usually, I take the scope off the mount at night, put it onto a flat surface and don't touch anything until the flat frames have been acquired.
From reading up on various forums, and asking questions about obtaining flat frames, I have settled on the routine of:
  • Stretching a white T shirt over the end of the telescope.
  • Use an LED tracing/drawing board to give an even light covering over the end of the scope.
When I first got my Hypercam 183c, I joined the Altair Astro Google Group.  On there, I made contact with RobinG (who I think is the writer of the Sharpcap software), and he offered the following piece of information on taking flat files with the Hypercam 183c, and how to work out the correct exposure etc.

Mean flat values to aim for in Fits Liberator
Taking this on board, I then set about experimenting taking single flat files and opening them in Fits Liberator until I achieved the desired values.  It's important to note that I leave the gain settings the same, and purely work with exposure length.  It's also important to note that the optical train remains exactly the same.  In other words, if all the images are taken using a certain filter, then that filter remains in place for the flats.
This is a screen shot of Fits Liberator showing where to find the mean values to aim for.

Fits liberator is free software available to download and use.  The image statistics highlighted in yellow is where to look for your flat files values.

So that's my workflow for a typical night's imaging.  It seemed quite daunting at first, but once I got used to it, I found that I can get through everything in about 30 minutes.  Many of these steps will be redundant in a permanent set up in an observatory.  That would be ideal.
Anyway, thanks for reading, and I hope you find it useful.

Tuesday, 11 September 2018

Astrocamp XIII - Cwmdu we had no problem.

Astrocamp XIII - I Was There.
A highlight to the year for many people.  The anticipation.  The constant checking of weather apps.  The buzz.  The laughs.  The astronomy.  The traditional post camp hangover.  This weekend, we returned to the familiar surroundings of Cwmdu campsite, and attended Awesome Astronomy's Astrocamp.  It was said that in all the camps so far, nothing had gone particularly wrong, and that if it ever will, it was bound to happen at Astrocamp 13.  A rather odd expression given that the whole event promotes evidence based science and rational thinking!  Quite amusing.

Arrivals T-1 day...
On the run up to camp, I had put forward the idea of having kind of a popup Astro DIY workshop and encouraged people to come along and show off their DIY modifications and projects.  I mentioned the idea on the camp Facebook page and was really pleased to find it well received.  Throughout the weekend, a variety of people stopped around where we were set up on the campsite and were keen to check out each others ideas.  Indeed, only this morning, I have been out and bought components and materials for my next DIY project.  More on that in future posts!
I decided to turn up a day early to give myself as much opportunity as possible to get some observing done.  This proved to be a good idea given the forecast for the main arrival day was for rain on and off throughout the day and evening.  With this in mind, I had packed plenty of different kit in the van which would keep me occupied for the weekend.  Boxes of electrical components, ongoing DIY projects, books and even the guitar made a rare trip out of the house.  I managed to get some observing in on the Friday evening and was pleased to observe the Great Cluster in Hercules, the Ring Nebula and Mars.  This was the first time I had chance to observe Mars for some years, so I must have spent 20 minutes or so looking at it alone.  Clouds came and went, but eventually covered the sky.

Arrivals Day...
Arrivals day at camp is brilliant.  A chance to catch up with friends from past camps, and just as important, to make new friends. This year, next to my pitch, I was fortunate to be joined by Raoul.  A first timer to camp, but not new to the hobby.  He brought with him various DIY projects including an array of Arduino based ideas that he was working on.  Perhaps the most impressive of his projects, and the one which I would consider trying myself, is a meteor detector which can detect the passing of meteors through the atmosphere regardless of weather or day light.  He demonstrated what was possible, showing us some recent recordings captured during the Perseid meteor shower.  Showers and cloud allowed me time to work on one of my own projects, and to solve an issue of dew bands not heating up when used with my DIY dew band controllers.  So, it was out with the pliers, screwdriver and soldering iron in the tent as the rain pattered down onto the tent roof. 

Day 2...
Sunday morning started early for me.  Not being able to train my body clock to simply allow me to have a lay in, I was up and about at around 6.30.  After the previous days rain showers and cloud, I was greeted by occasional patches of blue sky and some warm sunshine during breakfast.

Sunday is always a day I look forward to the most at camp.  It's the day when everyone moves down to the local village hall, and to the pop up pub 'The Spiral Arms'.  It's also the venue for the much anticipated pub quizzes and talks which are always popular and never disappoint.  This camp, the guest speaker was Libby Jackson who spoke about women who work in space.  Libby is author of 'A Galaxy of Her Own: Amazing Stories of Women in Space''.  A collection of stories about women who have made massive and significant contributions to space science and space travel throughout history.  It wasn't until Libby started talking about her research and her book that it hit me exactly how under recognised these women have been by the history books.  Her talk was incredibly enlightening, and now that I have returned from camp, I look forward to reading her book to learn more.  There are so many events that have happened in human space history that would never have been achieved without some significant and important contributions by these women, that it baffles me why they don't get the recognition they rightly deserve.  Libby's talk was by far the highlight of my camp and one that I will remember.

Back in 1973, the famous Welsh poet, singer and writer, Max Boyce wrote a poem about a legendary event in Welsh rugby history when Llanelli beat New Zealand 9-3.  But the event wasn't entirely about the win itself, but more that the pubs ran dry!  Well, at Astrocamp 13, Welsh history was to repeat itself once again, as indeed, the pub ran dry.  It made the final quiz of the day, dubbed 'The Masters Of The Universe' quiz all the more important as entrants were playing for a case of beer!
During the day on Sunday, a wave of optimism washed through camp as rumours spread of a window of clear sky that evening.  As people headed back to the campsite from the Spiral Arms, attentions turned to getting prepared for the potential of an evening of Astronomy.  I decided to set up my refractor and imaging equipment.  At first, given the forecast window of clear sky was quite short, it might have seemed a bit of a waste of time.  However, as readers of my previous posts might know, I have recently bought a new mount and I wanted to get some more use out of it.  I seemed to have had a good run of luck with regards to guiding and setting this mount up for imaging runs, so I wanted to confirm to myself that this wasn't by some sort of accident.  So, the only way to prove that my recent results haven't been down to pure luck is to ensure that everything is repeatable.  So, it was pleasing to see that once again, I was able to achieve a good guiding graph using PHD2.  But, perhaps even better, I was please to be able to demonstrate to some fellow campers the ability to polar align using Sharpcap Software, the ability to slew the scope to various targets using Cartes du Ciel and finally, to set up an imaging run.  My luck soon ran out though.  By the time I had achieved everything I needed to do and I was ready to start imaging, I only managed a single 2 minute exposure of Andromeda before the clouds rolled back in bringing proceedings for the evening to a close.  I'll still chalk that one up as a success though.

Should I Stay or Should I Go???
Monday is the hardest day of camp for me.  Knowing that the end of camp on Tuesday is approaching, almost straight away, me and many other Astrocampers look to the weather.  The thoughts of the pending journey home.  This year, the forecast for the last night of camp was for very little observing opportunity because of cloud, and the potential of rain coming through during the early hours of Tuesday.  The possibility of dropping a bone dry tent and dry kit and then not have the problems of needing to dry everything out always makes the choice a tricky one.  Monday is the day of high tea on the common area of the campsite.  Everyone from camp gathers together to enjoy their last afternoon together.  It's a point in camp that I look forward to, but alas one that I did not attend this time around.  I made the tricky decision to bring my stay at Astrocamp to an early close.  Not that I rushed to get packed away at all.  I don't have much of a journey home.  So, at a leisurely pace, I set about getting everything cleaned up and helped out others where I could before loading the last of my kit in the van before heading home.  It's always sad to leave, but leave we all eventually must.

Looking forwards...
April 27th 2019 will see Astrocampers gather once again in Cwmdu.  With bookings due to open in around a months time, it's already a date put into the calendar.  This camp, I had a walk around the site, looking at the sky from different pitches to ones that I would normally consider.  On a small site such as the campsite in Cwmdu, you don't have a lot of choice, so it's often a race to get to the prime pace you want to, but I will be there, finger on the button and ready to book.  Already, I'm looking forwards to seeing my friends again, making new ones and swapping stories about what we have been up to over the Winter.
This camp has been a great reminder of what I missed back in the Spring, but at the same time, it's like I never left.  Putting on events such as this takes a team of very dedicated people, and it's only right that they be appreciated.  So, firstly, my thanks to Libby Jackson for coming to speak to us, and for providing me with my highlight of the whole camp.  My thanks of course has to go to the team at Awesome Astronomy, Ralph, Paul, John, Damien and Jen.  Every camp means another brilliant and memorable time to be had.  My thanks also to my friends and neighbours, old and new at Astrocamp 13.  You put up with me and always have time for me, which is truly appreciated.

Why I'll be at Astrocamp 14...
Many comparisons are made during various star parties between organising groups and venues.  Some of these opinions are formed on the experience and views of others by people who have never been.  I have always said that I intend to visit a selection of different events around the country.  Earlier this year, I attended the Spring Kelling Heath star party in Norfolk.  That is a huge event with hundreds of attendees spread across a very flat and well appointed site, with generous sized pitches.  Being in the East side of the country, it could also be argued that there is a better chance of having more observable nights, with slightly better weather than is experienced in the mountains and hills of Wales.  So why not return?  The reasons are numerous.  What Astrocamp brings to the table is what many perceive to be a much more friendly atmosphere.  I went to my first Astrocamp on my own several years ago, not knowing anyone.  By the end of that first camp, I had made friends for life and had been left with no doubt that I would return.  Undoubtedly, the key reasons for this were the smaller site which makes the whole event more intimate, the Sunday in the Spiral Arms and perhaps more than any other, the common area in the middle of camp.  This is the place to meet, to share stories and views through the eyepiece, and in the event of a cloudy evening, chew the fat over a couple of lemonades.  Would I go back to Kelling?  Not for a star party, no.  Astrocamp however is a completely different experience.

Thanks for reading!