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!