Sunday, November 25, 2012

Eclipse 2012 - what went wrong?

It's now been eleven days since we stood in the shadow of the moon and I have now been back home in Denmark for a week. After recuperating and trying to remember what my day job is about I finally have found the energy for a very unpleasant task: finding out what went wrong on eclipse day.

Recall, that we got to see the second half of totality, with only a thin veil of high clouds present. Recall also that my ambitious project of high resolution automated imaging through a 4" refractor was a complete and utter failure.

I have worked on this project for several months. When I think about how close to success I was and revel in the details of how it failed I can almost feel physically sick. But that is exactly what I need to do; revel in details, go through it all again and try to learn from it so that I can do better next time.

Here's what happened. I set up OK, got the scope pointed at the partly eclipsed sun. Got the solar image focused and framed OK using liveview in Imagesplus. Got Eclipse Orchestrator started. Entered the precise geographic coordinates and local time from my GPS. Waited, thinking that all was ready.
Nervously awaiting totality with set-ups ready and too many clouds.

That was my second mistake (I'll get back to what the first mistake was later). I should have noticed that several small details were wrong. First, the displayed UTC time was one hour late. Second, the simulated view of the Sun did not match reality: the moon was leaving the solar disc instead of encroaching upon it.

When I discovered this we were only 15 minutes from totality and everything was just accelerating. I also had to function as the astronomical tour guide for our party of 28 paying guests. Frantically, I double checked the GPS coordinates and time, nothing was wrong. I wasted precious time restarting the PC and camera. With only seven minutes to go, I converted my script into an emergency version with only the coronal shots present (never practiced that). However, as totality began I could not start the script. Thinking that the system had somehow frozen up I realized all was lost and let it go. Instead I just enjoyed the rest of the show.

Yesterday, I went though it all again. Connected the camera, started Eclipse Orchestrator entered the local time on the PC as 6.36 AM, November 14, 2012 timezone GMT+9. Just as I had eleven days before. I saw the exact same problem - instead of totality being two minutes away the moon was just a few minutes from fourth contact! Fiddeling around I discovered, with a sickening, sinking feeling in my stomach the root cause: I had chosen GMT+9 as my timezone - it should have been GMT+10!!!!

Consequently, Eclipse Orchestrator thought that we were one hour further ahead in time than we actually were. How stupid of me.

Oh, well.

I must have been mixed up mentally by the pressure in the days since we arrived in Queensland. The tour program was very tight and I had been away from the equipment for three days because we had gone to the outback and the Daintree rainforest. I do remember entering GMT+9 on the laptop several days before the eclipse. That was a ticking time bomb and I could not overcome it on eclipse day due to the mental and temporal pressure of the unfolding events.

In the end of all this I arrive back to the feeling that all eclipse chasers have when totality ends, no matter what: when can I get to see this again?

Animated satellite images showing the lunar shadow racing across Australia and out into the Pacific (click to enlarge)

Tuesday, November 13, 2012

Eclipse 2012 - the event

We got to see the eclipse!!!

We left the hotel as planned and arrived on time. The site was open, not commercial'ish and we had a private area at the best spot, looking over the Captain Cook Highway and out over the bay. The area was warm, there was not a lot of wind and there were no bugs. The air was very moist and clouds formed and dispersed very actively. Sometimes we a got a very slight drizzle. Not the best situation, but we have known all along that this eclipse would occur under complex and active tropical conditions.

Setting up, then waiting.
I set up the equipment: Borg 4" refractor on astrotrac with Nikon D300 controlled by Eclipse Orchestrator. I also got the H-alpha scope up and running for the guests. Finally, I put an old analog Nikon camera with color film and a 55mm lens behind our crowd so that we would be framed with the eclipsed Sun. Quite a lot of stuff to tend to this time. I am pushing it to the limit - got to remember to enjoy the eclipse with my senses and be mentally - even spiritually - engaged.

Venus rising.
All was ready. Venus rose - bright and steady - where the Sun soon would follow. We all took that as a good omen.

After first contact just eight minutes after sunrise, things seemed to progress very rapidly. The time from first contact to totality spanned just 54 minutes. Measured GPS position and time; entered into the software. Found the sun, focused using ImagesPlus, then went back to Eclipse Orchestrator.

Fifteen minutes before totality things started to go wrong. Large clouds started drifting past the sun. I noticed that Eclipse Orchestrators simulated view of the eclipse did NOT match reality. I scrambled - was the GPS coordinates entered wrong (no!), was the time (no!). Reboot and try again, same problem. If the software is not in synch with reality the images will not fire off at the right moments and all would be lost. Just seven minutes to go. Instead of just dumping the project and dedicating myself to enjoy the spectacle I frantically made an emergency script, using the last few minutes with my head at the computer screen. Suddenly totality started, but a cloud was blocking the sun - none of the usual ahhs and oohhhs from us all; more like a tense mumbling.

One percent makes all the difference.
I tried to initiate the emergency script but found that Eclipse Orchestrator was not responding. The fully eclipsed sun came out from behind the cloud only covered by a thin veil of haze. VERY BEAUTIFUL! All was lost with my imaging project. I ran up to the analog camera and fired off some shots of the spectacle.

I think we got the last two thirds of totality including the diamond ring and Baily's Beads. I spent too much time fiddling around and the whole thing ended before I could find myself mentally participating. Too much ambition, too little time. Leaves me a bit frustrated.

The inner corona and numerous prominences.
Still, the luck we had in seeing the totality at all was amazing. Moments later a large cloud came by and blocked the sun for ten minutes.Although a bit frustrated I am mostly very happy. I had fun doing the preparations and I will probably find time to analyze what went wrong and try again some other time. For the eclipse chaser there always comes another time!

Be sure to click all the images to get a better sense of what happened this morning. The photographer is Inge-Lise Krylbo, one the participants on this journey. More photos will follow in the coming days and we'll also hear about how it went for other observers here in tropical Australia.

Eclipse 2012 - this is it!

It is 3.00 AM. Spent all night preparing. Sky looks promising; about 70% clear. Packing up and eating some food. Will meet with one of the guests who knows about weather and confirm that we are going to our primary site.

I am nervous about forgetting some essential piece of hardware so I better finished. We are leaving in 40 minutes. Next update will be after totality!

Eclipse 2012 - update before totality

>>>>>>>>  This update posted 1.5 hour before we leave the hotel  <<<<<<<

I put the gear together - went OK. Found that the 4" scope was out of collimation, as expected after the outback roads. Got it collimated OK. For this I used my artificial star, but had to pause halfway into the process because it started to rain. These tropical drizzles just come and go all the time! Scary.

Checked the Eclipse Orchestrator script once again. Found that the image sequences for the Baily's Beads and the Diamond ring effect were switched around on both sides of totality!! I got them switched around so that prior to totality the Baily's Beads comes first, then the diamond ring. Reverse after totality. Whew... Good I discovered that! Ran the script and saw that camera performs as it should.

I can't practice polar alignment on stars due to too many clouds, so I am opting for using the compass instead. Adjusted the astrotrac wedge to 16.5 degrees south. Adjusted the compass to 7 degrees eastern magnetic declination. This will have to do.

Our planned location - 2 km north of the centerline.
I'll transport the gear semi assembled, with the Borg scope in my hands in the bus so that it doesn't get shaken too much. The guests really want to help so they'll get to carry as well.

We'll have to drive 15-30 minutes south of town to a site just 2 km north of the center line. The bus leaves at 3.30AM - just 1.5 hour from now.

Just went outside and looked at the sky - it is clear! Orion and Sirius are near zenith.

Below is a NOAA IR image of the cloud situation 45 minutes ago. At that time it was cloudy here.
NOAA IR enhanced image 14.11.2012, 1:09AEST.
Red cross shows our location

Eclipse 2012 - arrival in Port Douglas!

We have just arrived in Port Douglas - the place where we will (hopefully!) be seeing the total solar eclipse. We are now just 11 hours from totality and I have a million things to do, mostly dealing with setting up the hardware. We have been in the outback and rain forest for three days out of contact with  the world.

I brought the telescopes along in the bus. That was a mistake. We've been bumping around on the roughest roads ever and the collimation must be way off by now; gotta check that shortly.

I'm back in a hotel room with Esben, our snoring tourleader. That doesn't matter much because I won't be sleeping tonight anyway. We have chartered a bus to pick us up here at 3.30AM to be at our designated site - south of here - at 4.00AM. I'll do a last minute weather satellite check and if there are clear indications that the chances will be better up north we will drive that way instead. I hope that won't be necessary.

Check out the latest weather outlook below. Scary!!!!

Latest outlook. Why do they show those nasty icons when only 'trace amount' of rain are expected and the cloud cover is 'only' 19-31%??????

Saturday, November 10, 2012

Eclipse 2012 - bad night, good news

I just had a pretty bad night; had to share a room with Esben, our tour leader from Viktors Farmor. He's really a nice guy but he snores - and it was very hot. Didn't get much sleep. I'll have to do the same on the night before the eclipse.

I used the night to charge as many batteries as I could - will do the rest in the coming days.

Just before leaving for the Bama way I checked the weather outlooks. They have improved relative to yesterday; see below!!!

Eclipse day weather outlook - not bad!!!

Eclipse 2012 - Queensland

Today we arrived in Queensland - the tropical north-eastern part of Australia where the total solar eclipse will take place just 3 1/2 days from now. It was cloudy 90% of our time in New South Wales, it was cloudy out of the airplane window all the way up here and it is cloudy right now. So much for the sunny, arid continent!

After arrival we learned that the itenary will take us up the 'Bama way' which is an aboriginal rainforest, outback path inland that should be very fantastic to experience. The catch is that we will not be able to bring any luggage of significance - hence I will be separated from all the astro-equipment that I was planning to start putting together in the coming days. Doing final practicing, alignments, checking. Now I won't be able to do that until just 10-12 hours before the eclipse!! Good thing that I practiced a lot at home.

On the Bama way: Willie Gordon, elder of the Nugal-Warra people

Friday, November 9, 2012

Eclipse 2012 - Siding Spring Observatory

Visiting comet-guru McNaught at Siding Spring.
Touring Siding Spring Observatory was great fun. We met Robert McNaught, discoverer of 73 comets and 410 asteroids, and heard about his work. We saw the great telescopes and took in the beautiful landscape views from the mountain.

Observing an outburst on the Sun
We have finally been getting a few minutes of sunshine in the mornings and I have started setting up the H-alpha scope for solar viewing with our tour guests. Yesterday witnessed an outburst from active region 1611 near the limb of the Sun. I hope that this region and others like it will be present during the eclipse next week - the more action the better on eclipse day.

Today we will leave New South Wales and fly north to Cairns. Mentally and physically this signals the next - eclipse - phase of our journey. Up until now I have not pulled out the photographic setup from my baggage stores, but starting tomorrow it will be time for that. I really hope there will MUCH more clear skies up north so that I can get som sky-time for the final preparartions.

Wednesday, November 7, 2012

Eclipse 2012 - script design

I have now finalized the design of the pre-programmed sequence of images to be taken during totality. Recall that I will be using a Nikon D300 DSLR with a four inch f/6.4 refractor on an Astrotrac equatorial mount. This setup will be under fully automated PC control using the 'Eclipse Ochestrator' software.

In China (2009) I used a similar setup but failed to get good images because the time interval between images was too short, causing the camera to freeze up. This time I am using a camera recycle time of 0.8 seconds which I have previously found should avoid this problem.

My setup is quite heavy and on the limits of the mount capacity. Consequently, the whole thing is fairly prone to vibrations. To minimize the risk of shutter induced vibrations I'll use a mirror lock-up time of one second. Still, from previously testing, I do expect that a significant fraction of the shots will be blurred due to wind induced mount vibrations, so it is important to shoot as many images as possible.

Using the script wizard in Eclipse Orchestrator I can generate a rough initial script to see how many shots can be pressed in during each brief phase of the eclipse. The program also chooses reasonable exposure times based on the actual setup.

I tweaked the auto-generated script so that the Earthshine shots were centered on the deepest part of the eclipse. I could also press in one extra corona image series plus a few extra corona shots here and there. Click the image below to see an overview of what I'm going to attempt. When running the script with the camera connected I see that the exposure settings are updated correctly and that the camera does not lock up. Hurray!

Camera control script - click image above to get full size version
I chose to use ISO=200 for which Eclipse Orchestrator suggested these exposure times:

  • partial phase (with filter): 1/1250 sec.
  • diamond ring: 1/160 sec.
  • Baily's beads: 1/8000 sec.
  • chromosphere: 1/5000 sec.
  • prominences: 1/2500 sec.
  • Earthshine: 3 sec.
  • corona: 1/640, 1/200, 1/80, 1/30, 1/10, 1/4, 1/1.3 sec., corresponding to optimal coronal imaging at Rs=0.1-4.0
I hope that these times will prove to be OK!

Yesterday we approached Coonabarabran and on the way experienced the world's largest solar system drive. At the Jupiter stop, 22 km from Siding Spring Observatory, I couldn't resist attempting some serious observing!

Getting up close to Jupiter (click to get even closer!)

Eclipse 2012 - clouds and wine

Lowe winery tasting

After leaving Sydney we drove to the Blue Mountains, stayed at a great, old timer hotel and drove on into gold and wine country around Mudgee. Although the weather has been nice and warm it has also been partially cloudy and I haven’t had a chance to set up the telescopes and practice polar alignment. Due to jet lag during the first days here I usually wake up around 4 AM. Later on I have made a habit out of this since these quiet, early morning hours are great for working on the various remaining tasks for eclipse day.

I did manage to get the bulb exposure mode on the Nikon D300 working under PC control. I’m not quite sure what did the trick but now it works anyway. This is important because the bulb cable should enable a larger number of images to be taken during the all-to-brief moments of totality. I must remember to re-check that this continues to work in the coming days.

It will remain cloudy for the next few days and during this time I better get finished with the Eclipse Orchestrator script and the eclipse presentation I'm going to be giving to the guests on this trip. It really is too bad with the clouds! Tomorrow we will be going to Coonabarabran and the famous Siding Spring Observatory. This will be great, but with all the clouds I doubt that we'll get any night time observing done. Grr. Still, you can't have everything and as long as we don't get clouded out on Nov. 14th I'm not complaining!!!

Sunday, November 4, 2012

Eclipse 2012 - Sydney and bulb exposure

Today we toured Sydney - Bondi Beach, the harbor, the Rocks, etc. Great fun, great weather and great food. Still, I am looking forward to leaving the big city behind and heading off to the Blue Mountains tomorrow. For me, nature and the landscapes have more allure.

I left the rest of the party early after dinner since I wanted to work more on controlling the Nikon D300 DSLR camera. I hope to get some clear, dark skies for doing star cloud photography in the coming days. I'd like to expose for maybe 1-2 minutes and this will require using the bulb exposure mode. I do have both a USB and a bulb cable - but for the last couple of times I couldn't get the setup to work. Only non-bulb exposures up to 30 sec are possible. What's wrong?

I have tried doing a bulb exposure using both ImagesPlus and the DSUSBcheck software that comes with the Shoestring shutter control cable. Doesn't work. I can do non-bulb exposures under PC control. I can do a bulb exposure without the PC, by just holding down the exposure button on the camera. What is wrong? I'm suspecting some weird camera setting is causing this. I have requested to join the ImagesPlus forum on yahoo groups - maybe someone there can help!

Other important tasks in the coming days: practice polar alignment using the southern stars; finalize the Eclipse Orchestrator script, finish preparing the talks I'll be giving to the guests. It's a hard life being a solar eclipse chaser - but someone's got to do it!

Saturday, November 3, 2012

Eclipse 2012 - Finally on our way!

Now the journey has really started. I am writing this after 33 hours of airline travel interspersed with a few sporadic hours of sporadic sleep, followed by 12 hours of touring Sydney. Everything has gone well so far. I have met many old companions from earlier eclipse expeditions and some new acquaintances. We flew with the largest passenger aircraft in the world from London via Singapore to Sydney, the Airbus A380. I tried running up and down on a staircase in an airplane - never done that before. In Singapore I got an SMS from Ingrid, our oldest daughter and my eclipse expedition companion from 2008, that she had put a surprise in my baggage. I did not get a chance to find it until we arrived in Sydney - but what I found sure made me happy, see below. All in all, we have had many good omens on these first few days so I am upbeat about having success on eclipse day, eleven days from now. I still have some technical issues to go through and practice on before that happens, but for now I will very shortly retire into the bed behind me!

Some snapshots from the past days can be seen below - click them to enlarge.

Home, sweet home - our Airbus A380.
Tired travellers in Sydney.

A surprise note from Ingrid, discovered once we arrived in Australia!
(click to enlarge)

Wednesday, October 31, 2012

Eclipse 2012 - Packing up

Tomorrow is the day for departure. I stopped fooling around with equipment a couple of days ago and have been weighing and planning how to get everything down under. Thanks to the travel agency that I work for my baggage allocation has been increased. That helps, but the task still isn't easy. Here are the numbers for what is allowed:

  • Checked in: 32 kg, one bag (normally only 23 kg)
  • Carry on: 10 kg, one bag (normally only 7 kg)

A few days ago I did a rough weighing and found to my great relief that when all equipment was included I still had 4 kg left for personal items such as clothes and toothbrush. Whew - no problem!! I can live with that. A tube a wash detergent for travel use will come along.

Still, I do have some problems. I am concerned about fragile optical components: H-alpha filter, telescopes, eyepieces. These alone weigh more than 10 kg that I am allowed to carry on board. So here comes my little secret: in my jacket I will fill all pockets with little, heavy and fragile items - total weight of jacket is 5 kg! I'll be wearing this jacket while checking in - nobody will notice. Don't tell anyone. On the carry-on bag I am 2kg overweight and hope that it won't be weighed or that I can gain sympathy in the name of science if discovered.

Now, I just hope that I haven't forgotten anything!  

38 kg of astro gear!

Monday, October 29, 2012

Eclipse 2012 - Photographing star clouds

In addition to photographing the total solar eclipse on Nov. 13-14th in Australia I also want to get some shots of the southern star clouds. The galactic central bulge will not be visible at this time of year, but the Magellanic clouds will and they are my prime targets. The Astrotrac setup and DSLR from the eclipse photo project are great for this purpose - all I need in addition is a good photographic lens.

Shooting stars with a 50mm f/1.4 lens on the Astrotrac.
My choice is a 180mm f/2.8 Nikon lens. The small Magellanic cloud will fit nicely in the 180mm field of view (FOV); while the larger cousin will require a 1x2 mosaic to get some air around it. Yesterday night I tested this lens and the software for controlling the camera. Based on advice from my friends, I'm using ImagesPlus. I'm a total novice at doing such DSLR starfield photography, so just a minimum of practice beforehand is essential. I couldn't figure out how to use the bulb exposure mode (I do have the cable and it was connected), so my tests were done at 30 seconds exposure time, ISO800. I also couldn't figure out how to move the liveview zoomed region of interest around - maybe I'll have to read the manual!

Just to be safe, I'll also bring a 50mm f/1.4 Nikon lens. This is more forgiving of tracking errors and the larger field may be fun to use on the milky way.

Sunday, October 28, 2012

Eclipse 2012 - Testing, testing, testing...

The total solar eclipse in Australia will take place just 16 days from now. There is only four days until the journey begins!!!

Since the last blog post I have managed to get two more nights with testing the solar imaging setup on stars. Besides just gaining experience handling the setup I have investigated several issues:

Some drift measurements (click to enlarge)
  1. Polar alignment and tracking. Imperfect polar alignment leads to a systematic tracking error that makes the stars appear to drift across the camera detector. Sometimes I set up the mount roughly using a compass and other times I did a careful polar alignment using the Astrotrac polarscope. By shooting several images over a known time period the drift in pixels/second can be measured. Some results are shown in the figure at right - typical drift values are 0.05-0.5 pixels/second (0.1-1 "/second). Conclusion: accurate polar alignment is nice to have but not essential. Drift of the FOV should not be a problem if I tweak the framing 5-10 minutes before totality. Exposure times up to 5-10 seconds at f=640mm should not be significantly smeared due to such drift.
  2. Vibrations: On something like 10-40% of  these star test images do I see effects of vibration. This is the largest threat to obtaining sharp images! I am loading the tripod/astrotrac system to the limit of their specifications and when you do that even slight perturbations can induce oscillations. Conclusion: I expect that wind will be the main threat on eclipse day and that 10-40% of my images will show effects of vibration. There is not much I can do about it at this time.
  3. Refractor collimation: I checked the collimation of the Borg 100ED refractor used for this project using an artificial star. This method is easy to use and highly accurate. Collimation was nearly perfect, but I do not want to suffer from poorly aligned optics on eclipse day. Hence, the collimation gear is coming along. Conclusion: scope was very well collimated and I do have the required equipment (incl. a 7mm eyepiece and 5x powermate) packed.
  4. Resolution: the stellar FWHM in the central region of my images is around 3.3pixels=8". These values are fairly reproducible from focus run to focus run and from night to night. Conclusion: my  focusing hardware/method works. My magnification is not large enough to really sample the variations in seeing.
  5. Field flatness: halfway into these investigations I remembered that the large chips in DSLRs coupled with fast refractors typically do require using a field flattener. Fortunately, I had a TS 2" universal field flattener lying around and could easily pop it in with just the right spacing (120mm) to the DSLR chip. See the image below - the effect is quite substantial. Conclusion: use a flattener when using a DSLR camera!
Effect of using a field flattener
(click to enlarge)
I now feel fairly confident about the functionality of my setup, its limitations and my basic ability to handle it. I'm almost ready to pack!

In addition to photographing the total eclipse I also want to capture some telephoto views of the Southern night sky. In the next blog posting you can read more about how I hope to accomplish that!

Friday, October 26, 2012

Eclipse 2012 - Nighttime forays

Last week I finally got out under the stars with the solar imaging setup. Having tried it out with good success in the daytime the next level was obviously to do it during the night, using the moon and background stars as test targets.

Set up running at night (click to enlarge).
I got up around 4.30am and went to our garage which is located a couple of hundred meters from our house. I had to go down there because I needed a clear eastern horizon where the low, waning moon would be visible. The position in the sky was similar to where the Sun will be during the eclipse and hence the mechanical arrangement of the setup would be tested under realistic conditions. Polar alignment was done casually by just leveling the mount and aligning roughly towards north. Setting up went well - just twenty minutes after arriving on site I had focused and framed the moon in the camera. Tens minutes later I had executed a test script using Eclipse Orchestrator and was packing up. The entire operation took only 40 minutes! When packing up I discovered that the knob holding the tripod vertical shaft was not fully tightened. Whence the first lesson from this night: remember to check all knobs and make sure that they are tight!

Looking though the resulting images in the following days showed that the camera did respond to changing settings being sent from the PC - great (and unlike the situation I suffered from during the total eclipse in China!!). A typical image is shown below. I quickly zoomed in on the boxed region to investigate the images more closely.

A 2.5 second exposure at ISO200 made through the 100mm f/6.4 refractor.
The image above tells me several things. First the lunar disc size is very close to what I expected and hence the corona will fit according to plan (inner + middle regions are OK, outer regions not fully covered). Second, I should remember to rotate the camera so that east-west appears roughly horizontal (unlike in the image above!) since the corona is widest in this direction. Finally, the earthshine is well sampled; i.e. the choices made automatically by the script wizard in Eclipse Orchestrator seem to be reasonable.

Exposures like the one above also captured several stars. Measuring the diameter of these on several images  gives a FWHM of approximately 3.2 pixels or 7.7 arcseconds. This is quite close to what I expected from this setup. Nice.

However, roughly 20% of all the images revealed some sort of vibration. There was also a 30 second period where the tracking was poor so that images were smeared in right ascension. I do not know why. This really illustrates a main problem for this setup: vibrations and tracking! Hopefully, I will fare better next time by remembering to tighten everything.

Three images. The top is good - showing 3 pixel resolution. The middle suffers
from vibrations while the lower image reveals poor tracking. (click to enlarge)
I'll blog more after I have been out under the stars again. I need more experience with the setup. I also want to find out whether vibrations and tracking can be improved upon. I also need to know more about polar alignment issues and how much declination drift to expect. So much to do and so little time left!

Sunday, October 21, 2012

Eclipse 2012 - first field testing

Time is passing too quickly. Every other night I dream of technical details concerning Coronal photography, waking up after a few minutes. There are many details to worry about. Getting myself and the setup out under the skies, doing some test shooting on celestial targets, will help resolve many questions and quell my nighttime worries.

My first test was done in daytime, using the Baader solar filter. I wanted to practice setting up, framing the Sun in the camera field-of-view and focusing using live view on the PC. Running a full test script with Eclipse Orchestrator will also be useful: will the camera settings update correctly, will the tracking be good enough to keep the Sun centered throughout the session, will small sunspot details be visible?

Solar image through Baader  AstroSolar filter. Click to enlarge.
Just outside the dotted ring some broad, ring-like artifacts can
be seen. I think these are due to digitization levels becoming
visble after contrast stretching.
The first daytime session generally went quite well. Setting up was easy - I just did a casual polar alignment by dailing in my latitude on the AstroTrac wedge and orienting the setup axis roughly towards north. Focusing with live view worked well, tracking seemed stabile. I did not notice a lot of vibrations. At right is shown one of the images from the test script with 1/1250 second exposure time at ISO400. Small details in active region 11589 are visible. I did notice that these seemed to vary somewhat in visibily from frame to frame. Since the exposure time is very short I think this is caused by atmospheric turbulence. All in all I am quite happy with this first session as it did confirm the basic functionality of the setup.

However, what about doing all of this in the dead of night which is what I must be able to do in Australia next month? Will longer exposures remain sharp? Exactly how sharp (stars are great for gauging this)? The waning moon is a great test target since it will appear low in the eastern sky just like the eclipse. Read about my nighttime forays in the next blog posting.

Monday, October 15, 2012

Eclipse 2012 - orchestrating the event

Even if it is possible to avoid clouds, even if it is possible to haul a capable astrophotographic setup halfway around the globe and still have it functioning at the right moment - would I even want to operate it? In order to take exposures and continuously change camera settings I would be an operator of technical equipment, trying hard to keep cool and focused on the task. I would not be able to personally - physically - immerse myself in the experience. Anyone who has ever witnessed a total solar eclipse knows that missing out on the experience is completely unacceptable!

Eclipse Orchestrator in action - just before second contact.
For those that have DSLR cameras a very elegant solution exists to this problem: a piece of software called Eclipse Orchestrator. This program controls your camera via a cable, firing off shots at precisely the right time and with precisely the settings you have pre-defined. What's more, it aids in designing just the right sequence of photos for your setup, your location and the specific eclipse. Using coordinates and a time signal from a GPS receiver on eclipse day this enables a precise timing to within 1-2 seconds; i.e. you can squeeze in the maximum amount of possible shots at just the right moments. And the best thing is: after setting it all up leisurely in advance any remaining involvement from your side is minimal!

Me using Eclipse Orchestrator during totality in China, 2009.
I tried using this arrangement during the total eclipse 2009 in China. However, back then I had not paid enough attention to practicing beforehand. Consequently, I did not discover that the script I had designed caused the updating of camera settings to lock up around third contact. I got some good shots of Baileys beads, the diamond ring and the chromosphere - but all my corona shots were underexposed!!

This time around, I am practicing more. I am running the script over and over in my living room, noting how many shots I can press in without problems; making sure that the camera operates as required. So far, I'm going for this during the most crucial moments:

which amounts to 73 exposures totalling 5 GB of data.

However; more preperation is needed. How do I know whether I can even achieve focus with this setup of borrowed parts? How long will it take to set up? Will the camera shutter cause significant vibrations? How long will my batteries last? Will my resolution be good enough - across the field of view? And what about the unforeseen problems I haven't even been able to think of? Testing under the skies - on celestial targets - is needed and next time I will talk about how that is going.

Saturday, October 13, 2012

Eclipse 2012 - with a little help...

Astrophotography can be very unforgiving - the slightest mistake or imperfection can make itself very obvious or completely ruin the attempt. An extreme example of this is total eclipse photography. The entire event lasts only a few minutes, the diamond ring part just seconds. You cannot practice beforehand on the real thing. You have to travel thousands of kilometers - with severe weight limitations - and work under unknown field conditions. High resolution closeups come with added requirements for tracking, mechanical stability and optical perfection.

Having just the right kind of equipment helps enormously. I have a good, lightweight telescope (Borg 100ED) and a good, lightweight tracking device (Astrotrac 320TT) . I don't have a suitable camera. Nor do I own a suitable tripod or equatorial wedge. I do own lots of good stuff, but this is very heavy and optimized for deep sky work. The solution, of course, is right at hand: get a little help from your friends!
Anita and Henrik's equipment delivery service!
Minutes after emailing around I had numerous offers for high end DSLR's, graphite tripods and great telephoto lenses. A super stable and ultra compact wedge? No problem! I could arrange for one to borrow with just single phone call.

This is my fifth solar eclipse expedition and I have never had equipment as fine and capable as this time. Neither have my photography ambitions been higher. Here's a list of the final version of the photographic setup I have arrived at:
I had several other setup iterations in the past weeks before arriving at this list. Going through these would not have been possible without extensive help and advice from good friends. Have plenty of them and keep them near!

However, with all this great gear - how to avoid spending the entire eclipse working it all and not having time to experience the eclipse with all senses?? Stay tuned for the next chapter of this blog to find out.

Friday, October 12, 2012

Eclipse 2012 - Corona photography project

Imaging setup - Borg 100ED refractor,
Nikon D300 camera, Astrotrac TT320
equatorial mount and Induro carbon fiber
tripod. (click for larger view)
This is the second part of my blog essay about the total solar eclipse of 2012. I'll be posting frequent updates on preparations and - once the journey starts - how our progress is going towards the ultimate goal of witnessing this spectacular event.

Besides being a hybrid tour guide / tourist I'll also be an astrophotographer. My project is to attempt medium-high resolution imaging of the inner Solar corona. To this end I'll be imaging with a plate scale of 2.4 arcseconds/pixel using a DSLR camera with a four inch f/6.4 refractor on an equatorial mount. These days most of my spare time goes into preparing this setup for action.

The plate scale, i.e. number of arcseconds pr. pixel is NOT the actual resolution of the final image. This can only be measured on real images and it is affected by many factors, such as optical imperfections, mechanical vibrations, tracking errors, atmospheric turbulence, etc. If all goes really well I'm hoping that the resolution of my setup will be around 3 pixels = 7 arcseconds. This isn't high resolution compared to planetary or deep sky imaging, but it is in the upper realm of corona imaging. Space based observatories are the only routine means for observations of the corona and the best of these (SOHO's LASCO instrument) have a resolution of only 20 arcseconds. The very best ground based images can reach 3-4 arcseconds but this requires equipment and skills that I do not have!
Simulated field of view of my setup.
(click for larger version)
In the next blog posts I will discuss the ongoing preparations, how friends are helping and field testing under the skies.

Wednesday, October 10, 2012

Eclipse 2012 - Introduction

Totality in Turkey - 2006.
The Moon will cover the Sun (completely!) on November 13-14 as seen from Australia - and I'm going there to see it! I will be working for a Danish travel agency called Viktors Farmor (english translation: Victors Grandmother) as I have done several times before. Viktors Farmor arranges journeys worldwide and has total solar eclipses as a part of their repertoire. I have provided astronomical guidance during their trips to Turkey, Siberia, China and India. This time Viktors Farmor has planned what in my opinion is the most ambitious journey yet and this time I'll try to blog about the whole experience.

Besides general work as an assistant tour guide my job includes providing astronomy themed talks, guided tours of the Southern sky and planning activities related to the eclipse event. I started preparations over a year ago by reading up on Australian and Aboriginal astronomy literature. In recent months I have ramped up preparations of equipment that will come along for the entertainment of our guests and for photographing the eclipse.

In recent weeks the pace has quickened and I am now spending all of my spare time preparing - mostly equipment and talks.

In the coming weeks until departure day (November 1st) most of this blog will deal with technical aspects of the equipment. During the journey I'll post daily updates on our progress and weather outlook. Stay tuned, because this will be quite an adventure!

Wednesday, September 26, 2012

Tri-band solar imaging - part 6

In previous blog postings I have presented the tri-band Solar imaging technique and discussed related acquisition and processing details while showing a number of example images. So, what can go wrong when doing tri-band imaging? In this blog posting I'll be presenting some of the main problems I have experienced so far.
Tri-band image with no flat field correction

1. Flat fielding is always non-trivial, especially when working at high f-numbers where the shadows of dust particles become smaller and denser. With narrowband solar filters flat fielding by means of the usual sky-flat or lamp sources does not work. When just colorizing single-band H-alpha images there is so much activity across the image that a few dust shadows don't draw very much notice. With tri-band images, these dust artifacts easily become color artifacts which show up more readily on our mental radar. So, take the time to experiment with establising a flat method that works well on your setup. I have used defocussed images of spot-free regions near the central solar disc with reasonable success. Especially with maximum detuning is the need for a good flat field evident since the solar landscape here is more bland than closer to the H-alpha wavelength.

Flat frame with vignetting, dust shadows and Newton rings

2. Newton rings are a particularly nasty problem associated with an extremely narrow filter bandpass. They are caused by interference between reflections inside the optical system and are usually of quite low contrast (typically less than 1% of the total signal). Hence, Newton rings are most evident when the solar filter is detuned to reveal more of the photosphere. The problem is reduced when working with webcam-like imaging devices where drifting solar features are tracked across many frames, hence the rings are often partially averaged out. On my images Newton rings appear as curved bands which easily move across the field of view over time. This mobility is their main curse, since it compromises the ability of a normal flat field to deal with the problem. For the better part of two years I have tried all sorts of acquisition and mathematical tricks to control them without much success. In the end I started doing it manually in photoshop by drawing dark lines in a seperate layer on top of the Newton rings, then blurring and using them as a mask to selectively brighten the regions affected.

Full disc tri-band view, showing effects of filter
non-uniformity (AR1520, July 12 - 2012)
3. Filter non-uniformity exists to some degree for all narrowband filters across their field of view and is in fact one of the main factors determining the filter price tag. The effects can be mildly irritating when working with a single-band image. With tri-band images I experience it much more severely since it causes unwanted color gradients. In fact, with my Coronado SM60 H-alpha filter (a high quality unit made by David Lunt) this problem effectively prevents me from creating decent, full disc tri-band images. See an illustration of the problem at right. At higher magnifications this effect becomes less of a problem since you then more easily can apply the 'background flattening' technique I mentioned earlier.

4. Time: remember to hurry when acquiring the tri-band images! Color artifacts will arise if significant movement has time to occur between frames. Staying within 20-100 seconds should be OK for normal situations, but with very high magnification and/or very fast moving features the restrictions can be much more severe. If you get an X-class flare exploding into your face (like this one!) don't even think about try to get it in tri-band! Micro-flares are also very fast and usually not possible to capture properly - I just accept them as colorful little dots here and there.
Rapid development of micro-flares results in funny colors on tri-band images.
In the next blog posting about tri-band solar imaging I will present a bundle of shots of what I have achieved so far.

Sunday, September 23, 2012

Tri-band solar imaging - part 5

This time I'll discuss the kind of image processing involved in the tri-band Solar images previously shown here on this blog.

Frame selection, alignment and stacking (AviStack)
After data aqcuisition you'll have three data sets; one for zero detuning, medium detuning and maximum detuning of the filter. Before these are combined into a tri-band composite the image processing is the same as you would normally do. If you made a movie you’ll select, align and stack the sharpest images with software such as AviStack or Registax. You might also perform flat field correction. Finally, the images may be sharpened and perhaps also corrected for solar limb darkening. You can choose whatever you want to do – the only important issue is that you do the same for all images prior to making the tri-band composite, or else strange color artifacts may appear in the final image. I won't go into further detail here about these steps because they are not particular to tri-band imaging.
Wavelet sharpening (Registax)
Background flattening (MaxIm)

On close-up images, like the one in the example above, I often 'flatten the background' - i.e. adjust the brightness of non-active regions to a uniform brightness level. This deals with any uncorrected vignetting and removes solar limb darkening effects. Background flattening ensures that the maximum dynamic range is used for displaying details of the chromosphere and active regions therein.
I use Photoshop for the remaining process steps where the tri-band image is created. First, all three images are opened and then merged as red, green, blue channels in a color image. Be sure to maintain the bit depths of the original images - I typically work with 16 bits. You can assign the images in whatever way you prefer; I have mostly chosen to use the most detuned image for the red channel, the medium detuned as green and the H-alpha channel as blue. This makes 'energetic' features blue/green or white and more quiescent regions red/yellow. There is nothing 'correct' in this, just do whatever you prefer!
Alignment of RGB levels.

Next, use the move tool to align the RGB channels to each other, while using some distinct feature such as a sunspot for reference. You don't have to do this perfectly, it's always possible to tweak the alignment later on.

Levels/curves details
(click for large version)
The following steps consist of several levels/curve adjustments with the purpose of increasing brightness/contrast and achieving a suitable color balance. All of these steps are really subjective - click the image at right to see details of the method a have chosen to follow for many of my images.

To illustrate that the results can be very different according to taste, look at the image below and see what happens if the hue is adjusted differently!

That's really all there is to it. If you are skilled doing regular narrowband Solar imaging the extra steps involved in tri-band imaging should be no big deal. However, there are limitations and challenges - in the next part of this blog I'll discuss some of these!

The colors of a tri-band image are as much subject to personal taste as regular narrowband images. Above, I  made a major hue adjustment to achieve a completely different look! (click for large version)

Friday, September 21, 2012

Tri-band solar imaging - part 4

Solar features can evolve rapidly and hence the tri-band acquisition process must be completed before these changes become significant. If you don't hurry, 'false' colors will arise that reflect movements of gas rather than changing physical conditions on the Sun.

For high resolution imaging with a webcam or similar device the quest for getting many images to catch moments of good seeing must be weighed against this requirement. Also, the more you zoom in on the Sun and the more active a feature you are targeting, the shorter the available time will be.

It is not possible to pin down a firm limit, but with my targets, preferences and setup (Coronado
SM60, f=1280mm, Skynyx 2-2M camera) I find the total available time to range from 1-5 minutes. Hence, if images are to be acquired for three wavelengths, the available time pr. wavelength is reduced to roughly 20-100 seconds. With my camera the acquisition rate is around 10-25 frames pr. second, hence each series consists of roughly 250-2500 images. Since Solar features change more rapidly in the chromosphere than in the photosphere, the time restrictions are least severe when the filter is detuned the most from the H-α wavelength. Consequently, images with the largest detuning from H-α ‘last longer’ for tri-band work.

Many filters are tuned mechanically in seconds, by tilting or by using a pressure regulator. A fast tuning mechanism is obviously best suited for tri-band imaging. Other filters are thermally tuned which is a slow process that requires several minutes to reach equilibrium between each wavelength change. With such a system, one could opt for ‘dual-band’ imaging where only two images are acquired for the red and blue channels, respectively– one at the H-α wavelength and another at maximum detuning. A green channel can then be synthesized as an average of the two other channels. An example is shown below. For this image a Daystar Quantum SE 0.5Å filter was used with 6562.8Å for the blue channel and 6563.8Å for the red channel. The result is not as rich in color variations, but I still consider it worth the effort.

Dual-band image of AR1195 from April 25, 2011. Daystar Quantum SE 0.5Å H-alpha filter.
Below is another shot - this time a real tri-band image - of AR 1087 on July 10, 2010. This was acquired using a Coronado filter that was detuned by tilting. The colors are obviously better.

Tri-band image of AR 1087 from July 10, 2010. Coronado SM60 filter.
Tomorrow I will discuss the processing flow I use for making these images. A lot of it is standard stuff for Solar work, and the tri-band part is actually quite simple.

Thursday, September 20, 2012

Tri-band solar imaging - part 3

In the previous blog posting I posted a question: how will spicules and prominences appear at the solar limb? I am using a color scheme that arranges the most detuned image as red, medium detuned as green and not-detuned as blue. When seen in silhouette against the photosphere spicules and filaments are revealed by their absorption of H-α light. They look dark in H-α images and since this is blue in my color scheme they will appear reddish. When seen against the blackness of space these same features are revealed by their emission of H-α light - and appear bright in the blue (H-α) channel. Check it out for yourself below!
Active region 1193 on April 22 -2011, with many internal color variations. The chromospheric limb appears bright blue since here we see H-alpha emission which I choose to map into the blue color channel. When seen against the photosphere the same features are revealed by their H-alpha absorption and thus appear reddish. Click image for full size view.
Now, take a shot and guess how a flare will appear in a tri-band image! I will show a picture of one later.

I had a hard day at work and blogged too late into the night yesterday, so you'll have to wait until tomorrow for the next posting where I will discuss acquisition aspects of tri-band imaging.

Wednesday, September 19, 2012

Tri-band solar imaging - part 2

Detuning by tilting - Coronado's T-max tuner

The Sun provides so much radiation that a tiny wavelength interval can be selected to enable viewing of certain layers of the solar atmosphere or certain elements – and still have plenty of light for fast exposures that freeze the seeing. Most notable is the hydrogen alpha (H-α) transition at a wavelength of 6562.8Å. Emission at this wavelength is a sign that hydrogen is being ionized and it comes predominately from the solar chromosphere. Narrowband solar filters can be detuned slightly to maximize contrast or to allow observation of Doppler shifted light from features that are moving rapidly along our line of sight. The tuning range is typically very limited – around one angstrom – but even such small changes lead to dramatic differences in the resulting image. I use a Coronado SM60  H-α  filter that can be tilted slightly using  the so-called T-max tuner; see the photo above.

Rates of change in brightness of various features with filter detuning and how they relate to colors in a tri-band image
(click for bigger version)
The figure above shows a typical scene, captured with this filter at three different wavelengths. The targeted object is active region 11087, which consisted of a small sunspot 20” across and a complex magnetic field which produced several low-level flares during July 2010. At the H-α wavelength of 6562.8Å (corresponding to zero tilt), the field is covered with spicules and contains two dark filaments and a bright region of plage. In all this action the small sunspot almost gets lost, with only the umbra standing out clearly as a dark, irregular spot. At 6562.3Å (half tilt) the contrast of the spicules, filaments and plage decreases. At 6561.9Å (maximum tilt) these features are nearly gone so that the sunspot with penumbra becomes clearly visible. A smaller spot, unnoticed before, becomes apparent towards the upper left.

As the wavelength is tuned away from the H-α transition we are viewing more and more light from the underlying photosphere. What is especially interesting in this regard is that the rate of change in brightness with wavelength is different for various features, depending on what they are. It is not the same everywhere. Hence, if detuned images are used as separate color channels in a composite image various colors will appear that represent different rates of change. This is evident in the tri-band image above where the R, G, B channels are chosen as most detuned, medium detuned and not-detuned, respectively, from the H-α wavelength. In such a color scheme the underlying photosphere appears yellowish, spicules and filaments are reddish, plague is white, etc.

Tri-band image of AR1087 in a quite moment. This active region had a beta-gamma magnetic field and harbored multiple M-level flares during July 2010. Click to enlarge.

Many more colors can be found in this way on the Sun and I'll be showing more later on. For example: how do you think the chromosphere and prominences at the solar limb will appear in a tri-band image as the one above? See for yourself in tomorrows blog posting!