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See individual exposures of
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See fascinating time-lapse photography
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Total
Solar Eclipse, August 1st 2008
Observers report
from centre line NE of Jiayuguan
by
Joe Cali
On July 20th at 1:30am, I arrived in Beijing having flown from
Australia. After a short hold up at the airport while customs
decided if they would let me import the telescope in my suitcase,
they said it was ok and let me go on my way. My friend Bengt
Alfredsson was on his way from Sweden and arrived in Beijing 12
hours later. We spent ten days blistering our feet,
pounding the pavements in Beijing, Xi An and Shanghai travelling
under our own steam. On July 31st, Bengt and I joined up
with the Eclipse City / Eclipse-Reisen 48 hour eclipse program
including a charter flight to Jiayuguan ex-Shanghai.
Forbidden City Beijing
Park of peoples Beijing
Terracotta Warriors,
Xian
CCTV Tower Beijing
Beijing Chengxiang
Huamao Shopping Centre
Shopping Centre downtown Xian
Zhongda International Xian
Travelogue
We rented a pair of suites in Shanghai & spent five days looking
around. On the first night we walked along the street near
our apartment building. Bengt looked at a pizza joint. I said,
"Don't even think about it, we are eating local tonight!"
We walked into a hotpot restaurant. Neither of us spoke a word
of Mandarin or Shanghaiese. It was a typical Shanghai hotpot
restaurant - a small stove in the middle of the table -
order the ingredients and a pot of stock and cook it yourself.
The menu had no English translation and no pictures. So
I said to Bengt, "What if I just tick a few things at random?
How bad could it be?" Bengt just raised his eyebrows.
After 15 mins a waiter arrived carrying a large stainless
steel pot about 40cm diameter. He set it down and we looked
in. To our horror, we saw a bowl full of fish heads floating in
grey coloured water sloshing around in what must have been about
40 chopped red hot chilies. Bengt didn't say a word, he just looked
at me, raised his eyebrows smiled and nodded. After the initial
panic, I tasted some of the vegetables and seaweed that were lurking
beneath the surface. It was really very tasty. Later,
a waiter brought us more of the ingredients I'd randomly selected.
These included wonton noodles, brocolli mushrooms root vegetables
and seaweed. It looked horrendous and it was very very hot
but it was really very tasty. Next night however, we tried
the pizza restaurant!
Pudong Riverfront from the Bund
Nanjing Rd, downtown
Shanghai
New World Shopping Centre, Nanjing Rd
After a few days in Shanghai, we made our own way to the airport
to meet the Eclipse Reisen group at midday on July 31st.
I recall that at Shanghai airport they didn’t have a conveyor
belt to load luggage into the plane. I watched as two baggage
handlers threw my suitcase from the ground level up into the plane.
Great! Thanks guys. Air China’s bag handlers had already
been busy progressively destroying Bengt’s travel pack during
the trip. In Xian, we resorted to sewing up the damaged section
of his bag with a bootlace. My suitcase contained an 80mm
refractor OTA and an equatorial mount, mounting tripod and camera
tripod. We arrived in Jiayuguan at 9:00pm and went straight
to a downtown hotel to an EC welcome cocktail & briefing.
After the briefing we went out to the square to watch a cultural
stage show put on to celebrate the eclipse. We returned to the
hotel tired and after a high tech shower I went straight to bed.
At 1:30am hotel reception called to remind me that they would
be giving me a wake up call at 6:30am. Yep, thanks for that,
I said wondering why, in the name of holy snapping fluffy ducks,
they’d wake you up at 1:30 am to remind you they’d
be waking you up 5 hrs later. Bengt told me they did the
same to him.
I awoke to my alarm at 6am. We went for an early breakfast. By
this stage, I had not eaten for 24 hrs. I missed both lunch &
dinner the day before. Just as I was leaving my room, the phone
rang – my wake up call. Back to the room, grab the suitcase
and camera bag. The suitcase contained my telescope, mount, my
Manfrotto tripod Bengt’s Manfrotto tripod and a couple of
folding stools given to us by EC. It added about 6kg to the suitcase’s
usual 22kg weight. We were on the bus and on our way by 8am. I’ll
skip the fine details. During a busy morning we visited the Great
Wall’s first fire tower in Jiayuguan, the Jiayuguan Fortress
and the Jiaquan wine spring. Following a late lunch we made our
way to the eclipse site.
Jiayuguan First Tower
Lizard
Jiayuguan Fortress
We drove north east from Jiuquan. While on the bus, our Chinese
guide read out a statement from the Jiayuquan administration stating
that we were not permitted to use GPS for the purposes of mapping.
This received rousing applause from the passengers many of whom
were using GPS to track the bus at the time. Most didn’t
take it too seriously but approaching the checkpoint, there seemed
to be much activity switching off bluetooth and secreting GPS
units.
The
Police checkpoint
Eventually, we hit the police roadblock & check point.
Authorities closed access to the centre line to anybody who didn’t
have an Eclipse City pass. There was some discussion on
SEML that it sounded to some like dirty tricks by EC. But
in fact, the authorities just didn’t want any people wandering
around the area. There was a spaceport and military installations
in the area. EC managed to acquire access to just one site
in our area and another further west both were heavily guarded
- guarded to keep us corralled in the one area. Anybody could
obtain a pass from EC. At the check point, the police checked
that we had our all-important Eclipse City passes. After
much fiddling around, videos & photos with the police and
other activities we cleared the check point. I heard a rumour
that someone managed to lose their pass and was put off the bus
but I didn’t see this myself. It was made abundantly
clear to all of us that without these passes we wouldn’t
clear the checkpoint.
After the checkpoint, the GPS units came back out. The ban notice
that had been read out specifically mentioned a ban on using GPS
for the purpose of mapping activities. Fortunately most people
on the bus were using GPS units for the purpose of tracking our
movements, for timing or to pinpoint their observing location.
Nobody was making maps so most participants decided to leave their
units running.
We drove 60km NE of Jiuquan. In the north, a large bank of stratocumulous
clouds threatened and we were driving further and further under
them. The only hope was that they'd vanish or blow away
as the temperature changed. I'd seen this happen before.
We finally arrived on site about 90 mins before first contact.
Eclipse City (EC) chose this location about 2km south of the centreline
and 1300m altitude because of its scenic aspect. If you were just
watching the eclipse, the site was fantastic. But our group
included many keen eclipse chasers using equatorially mounted
telescopes. Some carried heavy cases for about 500 metres
over soft sand to get to the ridge that provided the most scenic
view. I don’t want to be too critical because I know
that EC had to do a lot of groundwork with Chinese authorities
but it would have been nice not to have to carry the gear so far.
Although Bengt and I shared the carrying duties, we were trying
to hump a 28kg case over soft sand.
Bengt Alfredssons GPS registered the following coordinates
at our site
| Latitude |
40 degrees 23 mins 21.3s |
| Longitude |
99 degrees15 mins 02.8s |
| Altitude |
1325metres |
As you will see from my wide field images, we stopped well short
of the ridge. Basically we were about as close to the buses as
we were allowed. A number of factors affected this decision.
I was concerned about how long it might take to walk up there
and how long it would take to pack up and return. The
view of the landscape was better up there but the ridge lined
with observers held its own attraction. Our guide incorrectly
told us we had to be back on the bus at 730pm local time - 15
mins after totality. I doubted that anyone would return to the
bus by 7:30 but by choosing a closer location, I could wait until
I saw others walking back and perhaps work that little bit longer.
I have been developing a small lightweight single arm fork
mounting since TSE 2001. The entire dec fork arm can
move along slots to balance the load around the polar axis negating
the need for counter weights. It fits in my suitcase with the
80mm f7.5 refractor OTA and all my clothes for a grand total of
21-22kg. I assembled it over a 20 minute period. The was a bit
of breeze so I collected rocks in a large plastic bag to weigh
down the tripod and stabilize the mount.
All went smoothly until I attached the stepper motor and switched
on the drive control. The indicator lights didn’t light
up the right way. I immediately started prodding & poking
plugs and connectors. Then I saw it. I’d assembled and tested
the drive at home in Australia and again in Shanghai but between
Shanghai and the eclipse site, two motor wires were somehow torn
out of the motor body. I thought everything was packed well enough
but apparently not. I remembered seeing the suitcase thrown at
the airport. Could that have been the fatal blow? At the
observing site with 20 mins until C1, there was nothing I could
do but disconnect the motor. I have a "failsafe" slow
motion knob on the other end of the worm so that, in case of drive
failure, I can turn the worm by hand.
Some days before the eclipse, I calculated that at 9:58:30 UT(14.5
mins before totality) the azimuth of the Suns north limb would
lie exactly west. I looked as the shadows grazed along the flat
flange plate of the declination arm. This confirmed that the polar
axis was indeed pointing north.
The Sun played
hide and seek with the clouds until 20 minutes before totality
when the cloud
seen below and to the right of the Sun finally drifted away. Looking
at the direction of drift
I confidently said to Bengt that we were in the clear. The
other two clouds to the left, drifted
west & can be seen in the totality images beneath the Sun
in the distance. This picture was taken
approximately 15 minutes before second contact. The Sun remained
visible from this point until totality.
Observing program
Sunspotting
80mm f7.5 ED refractor
The motor failure threw my detailed plans into some disarray as
I quickly reassessed my photographic program. I decided
to abandon planned time-lapse photography of the partial phases
to concentrate on successful coronal photographs. The time saved
would give me a chance to try a dry-run for the coronal photography
sequence using manual operation of the worm drive. To operate
slow motion, shutter speed dial and cable release requires 3 hands.
So I needed to work out the best way to do it. I found that
using the left hand for holding the shutter release and driving
the worm and the right hand for changing shutter speeds was the
way to go. The OTA is a Chinese ED80f7.5 refractor with a Pentax
K10D 10MPx DLSR attached. I hope to have completed an automated
exposure control program and interface for this camera by next
years eclipse but this year I was employing a capture protocol
based around the camera’s built-in 5 stop auto-bracketing.
A 600mm focal length and 15x23mm sensor meant that exposures longer
than 2s were not necessary as the corona would be over exposed
in the entire field. Exposures longer than 1s would blur due to
the absence of a drive.
Task:
photograph the corona at all shutter speeds between 1/4000s and
2s.
Wide field cameras
Next I set up two wide field cameras on one Manfrotto tripod using
a simple Aluminium RHS mounting bar.
Video camera
One was a Panasonic VDR-D150 standard definition Video camera.
The camera has an excellent quality Panasonic 30x lens 1.9-57mm
FL (35mm equivalent 35-900mm) The lens has low flare. On this
occasion I added a Marexar Ultrawider wide angle adaptor.
I bought this adaptor for my 35mm camera in 1979 when I was a
struggling student and couldn’t afford a real wide angle
lens. Although I have various wide angle lenses, I continue to
use this attachment for various applications. Attached to
the Videocamera it creates a circular field, clipped top
and bottom by the frame - 140 degrees across and 90 degrees vertical.
Task:
photograph the passage of the lunar shadow across the sky starting
2m before C2 ending ~2 mins after C3.
Still Camera (time lapse imagery)
The other camera mounted on the same tripod was a Pentax Z1 (35mm
film camera) with a Pentax SMC-M 18mm f3.5 lens loaded with Fuji
Pro H ISO 400 film. This model camera has a built-in intervalometer.
This is convenient for any constant exposure time series work.
I usually use it for automated photographs of partial phases before
and after totality and for automated wide field capture during
totality.
Task : Take
a time lapse, 1 exposure every 4 seconds starting 20 s before
C2 and continuing for 36 exposures(144 sec).
Both wide field devices work unattended after I press the start
buttons 2 mins before second contact.
Darkness Descends
Totality was approaching rapidly. I looked at my “Atomic
Clock.” It’s a small white faced analogue travel
alarm that I like to use for eclipses due to the ease of reading
the face. 11:10:10. Time flies.
I almost missed the start time for the wide field cameras. I
started the cameras on schedule but very nearly missed the window.
The shadow moved across from the northwest and pretty much right
on time we were treated to a beautiful diamond ring. The clouds
to the west acted as a wonderful projection medium for the celestial
animation that was the approaching shadow. Watching this as I
had in Libya, I mananged to repeat the error I made in Libya and
didn't remove the solar filter.
In Libya and again here I forgot to take off my solar filter and
to add to my woes, didn’t focus the telescope perfectly.
Watching the diamond ring naked eye and operating the camera by
feel, I managed to do it again. I didn’t recheck the
focus just prior to the eclipse and I didn’t remove the
filter. I didn’t look into the camera until 15 seconds
had passed by which time I’d completed 40 exposures
between 1/4000 and 1/8 seconds. By the time I’d taken those
40 blank exposures, worked out what I’d done and rectified
the problem, my first usable totality exposure was taken at 11:13:30
and I’d blown almost half of totality. I'm going to
invent a solar filter that takes itself off before totality ;-)
Despite making such an idiotic error, the auto-bracketing of the
Pentax K10D is very efficient. I had rehearsed the exposure sequencing
a number of times even with my eyes shut. The value of doing
this became very apparent. In the remaining minute &
a bit, I rattled off another 70 exposures. I completed my totality
exposures at all shutter speeds from 1/4000 to 4s. The reason
I make errors like this is because I do look around during the
eclipse. I operate the cameras by feel and don’t stare at
the camera the whole time. But this gives me the best of both
worlds. I do look through the camera to get a better
look at totality. The camera has a right angle finder that gives
me a great view. The manual slow motion also didn’t
limit me much. I allowed the camera to drift while I shot
the inner corona up to the edge of the field and re-centred only
for the outer coronal images where I needed the field positioning
to be correct so as not to clip the corona. The longest (2s) exposure
is blurred a little but this is only used for the very outer coronal
streamers which are pretty diffuse anyway.
Bengt and I even had a short discussion during totality about
whether we could see a “tunnel” or not. We agreed
that we could see an indistinct tunnel or coffee filter but it
was very wide and low to the horizon.
In this image the coffee filter or tunnel can
be seen wide and at a low angle to the horizon. The edges of the
shadow were about 100km away in each direction so it stands
to reason that the angle would be low and wide.
By contrast, the observations and photographs of the tunnels taken
in Australia in 2002 show the shadow edge
much higher in the sky. On that occasion, the edge of the
shadow was only 10km away in each direction so its
edge naturally appeared at a higher altitude. Image taken
at 11:13:37 seven seconds before mid totality.
Totality ended. In my rush to complete the full shutter
speed sequence, the diamond ring appeared while my camera shutter
speed was set too fast but I was just happy to have rescued the
situation.
Discussion
After some consideration, the appearance of the tunnel was probably
to be expected. The angle observed between the edges of
the shadow and the horizon and the maximum height of the bright
surrounding sky, can be calculated using simple spherical trig
expressions. The height is directly related to the diameter of
the eclipse path. On August 1st, the edges of the lunar
shadow were about 100km away in each direction and therefore lower
to the horizon and less distinct due to diffusion by the air mass.
By comparison, the much narrower path observed from Cameron Corner
in 2002 was only 20km diameter and only 10km in each direction.
As a result, the shadow edges were much higher in the sky and
more distinct because they are not being diffused so much by the
atmosphere. The observed angles of the shadow with the horizon
were correspondingly greater. Therefore, the best observations
of the spectacular tunnel apparition is best seen near the end
of eclipse paths that have narrow path diameters.
Videocam
This was my first attempt at video of an eclipse. Auto exposure
control worked very well. The wide angle view 140 x90 degrees
is a good field of view. I however didn’t think to turn
off the camera’s auto focus. The camera went hunting for
focus at C2 and C3 and the focus it found each time became progressively
worse. Before totality the camera was in focus, during totality
it was slightly out of focus. After totality, it found the
front element of the wide angle adaptor and focussed on that.
Even with the slight out of focus during totality, if viewed on
a small screen, the shadow progress has been recorded. The camera’s
audio recorded every exposure of my time lapse camera so that
I could work out the exposure times for those film images.
On the track I can hear the shutter of my K10D on the telescope
although with EXIF data, this is of less value. It also recorded
our conversation and ambient cheers from the crowd.
Time
lapse imagery 35mm film
The results of this project exceeded my expectations. I used my
trusty old Pentax Z1 35mm film body loaded with Fuji ProH ISO
400 film. The Z1 has a built in intervalometer and I fitted the
camera with a Pentax SMC K18mmf3.5 (ultra wide lens circa 1975).
It may be an old design but has low flare and is quite sharp.
Background. Bengt Alfredsson has for many years been taking
wide angle images of totality. He uses the Nikon 9 stop
bracketing facility in the MC21 remote control unit. Bengt shoots
4 sets of 9 stop bracketed exposures per 36 exposure film with
a 20mm lens. He triggers one at C2, one at C3 and the other
two spaced evenly between during totality. Using 9 stops
of bracketing he gets a lot of discards but the technique guarantees
he always gets some good images. In 2002, he took a stunning
image of the “tunnel” that was later published
in my eclipse chasing feature in Australian Geographic(Issue 78,
pp 86-99). Much to my horror and dismay, the photo was wrongly
attributed to me. If you see the article, the closing photo is
definitely Bengt's.
I don't have the luxury of choice. The Z1’s intervalometer
doesn’t allow bracketing to be combined with interval shooting.
I’ve noticed at previous eclipses in 2002 & 2006 that
the Z1’s auto-exposure provides perfectly adequate exposures
for very wide-angle imaging when metering mode is set to centre
weighted averaging. In CWA mode, the meter won’t pay too
much attention to the tiny coronal patch of light. Some evaluative
metering algorithms might weight it more heavily. In 2006
with the luxury of 4 minutes of totality, I triggered the Z1 camera
manually while attempting to shoot a horizon panorama. The resulting
images were OK but in the light of the results obtained this eclipse,
I think this approach of shooting a time lapse with a fixed camera
aspect is superior to a panorama or changing aspect.
During this eclipse a mere 113 s of totality demanded a hands
off approach. I loaded a roll of Fuji Pro H colour negative
film with its generous exposure latitude, I decided to use a fixed
camera direction time lapse approach to depict the shadow transit.
With only 36 exposures to play with (35mm film camera) some triage
was in order. I considered photographing in the anti-solar direction
but decided on a westerly aspect with the corona more or less
centred. With the camera pointed at the Sun, there was no point
allocating too many exposures after C3. The shadow would
be out of field quite quickly. So I started the camera at 11:10:25UT
(2m21s before totality). There was a 2 min delay until the intervalometer
started so the imagery began at 11:12:25UT or 21 s before totality.
My 36 exposures at 4 second intervals took me through to 11:14:45
just after 3rd contact.
Time of Exposure for each frame [±0.5s]
Exp # TIME
UT(H:M:S)
Exp #
TIME UT(H:M:S)
1 11:12:25
20
11:13:41
2 11:12:29
MID-ECLIPSE
11:13:44
3 11:12:33
21
11:13:45
4 11:12:37
22
11:13:49
5 11:12:41
23
11:13:53
6 11:12:45
24
11:13:57
C2 11:12:46
25
11:14:01
7 11:12:49
26
11:14:05
8 11:12:53
27
11:14:09
9 11:12:57
28
11:14:13
10 11:13:01
29
11:14:17
11 11:13:05
30
11:14:21
12 11:13:09
31
11:14:25
13 11:13:13
32
11:14:29
14 11:13:17
33
11:14:33
15 11:13:21
34
11:14:37
16 11:13:25
C3
11:14:39
17 11:13:29
35
11:14:41
18 11:13:33
36
11:14:45
19 11:13:37
The best way to view the results is to open the first image.
Keep your mouse on the NEXT link and keep pressing to shuffle
the images through as quickly as possible. I tried setting
this up in a flash gallery but this works better. The flash changeover
time is too slow. If you have a slow internet connection, go through
the images once to get them into your cache, then repeat &
you should be able to shuffle quickly through the sequence.
View
the Time Lapse Sequence
80mm f7.5 Refractor Photographs
As already mentioned, the images of totality are compromised by
loss of focus. My first reaction was to think that I’d
forgotten to focus the refractor but examination of the handful
of partial images indicated that the refractor lost focus between
an image taken 10 mins before C2 and another taken 3mins before
C2. Alexander Birkener and Ralf Schaefer mentioned that
they had measured a very large temperature drop of 27 Celsius.
The measurement was in sun not shade and taken 1 m above the ground.
It now seems that the temperature shift may have caused or at
least contributed to the loss of focus.
On the flight out of Jiayuguan, I completed a basic image stack.
I aligned all the images and created a set of masks to radially
blend the images. Joerg Ackermann was sitting in front of me and
very kindly didn’t recline his airline seat which allowed
me to use the laptop during the flight. By the time we reached
Xian airport, I had completed a basic image stitch. The
technique I apply is the same technique set out in Russell Browns
eclipse tutorial available on the Adobe site.
After applying the unsharped mask, the poor focus became obvious.
The unsharped mask did nothing to improve sharpness. So
I tried an unsharped mask filter. No matter where I applied it,
it didn’t improve things. There is a technique I sometime
use to “rescue” images my photography students have
taken when they haven’t focussed on their intended subject
or have too much camera shake.
Step 1 Make a copy of the
layer
Step 2 Apply a high pass
filter to it. This filter can be found in the “other”
group of filters right at the bottom of the filter menu.
I used a 3 pixel offset.
Step 3 Set layer blending to overlay
This sharpening technique improved the apparent focus dramatically
and has lifted the quality of the resulting composites from garbage
to mediocre.
I then used combinations of other techniques including alpha channel
contrast masking, 3d render scripts, unsharped masking ( filter
and spin ) to create the set of final images. With limited
fine detail available to me, I have played around in processing
some images to show large structures (low spatial resolution)
at the expense of fine detail.
View the individual exposures
in increasing exposure order
View the image composites
Looking ahead
Mount
Next eclipse is of course July 2009. My development of the
mount is almost complete. The refractor mount and my clothes all
pack into a suitcase that weighs in at 20kg. I need to upgrade
the mediocre worm drive with a more accurate drive. It may surprise
some but I've set up a numerical model for a tangent drive and
determined that for a solar eclipse instrument, a tangent drive
has some advantages. A bisymmetric tangent drive is one
that starts with the arms apart , the arms become parallel halfway
through its operation where the drive performs very accurately
then drives the arms apart again. The advantages of tangent arms
are found in lighter weight higher torque for the total weight
of the drive and much higher drive accuracy during totality when
it’s needed at the expense of less accuracy during partial
phases when shutter speeds are fast and accuracy isn’t needed.
The problem is that for a custom mount like mine, you can't easily
buy very small lightweight worm gears that are also highly accurate.
Bisymmetric
tangent drive error. During a 10 minute window either side of
the centre position, the error in the drive rate is better than
±0.01 arc
sec per sec. Provided the drive is well made that translates
to a drift of 0.1 arc sec during a 10 second exposure, a typical
maximum exposure
during totality. It is relatively easy to manufacture a
high precision tangent arm, compared to a worm drive.
Beam Splitter
I have acquired a 1/10 wave 50% beam splitter plate. I will
be building a beam splitter box for the back of the refractor.
Similar to a flip mirror box, it gives me simultaneous optical
viewing and photographic acquisition during totality for the loss
of one stop of light.
Automated Photographic Acquisition
The Pentax K10D and K20D have an analogue bus between the body
and the battery grip. Shutter speeds can be shunted up and down
by closing a switch between a common pin and one of two other
pins; one that shunts the shutter speed up, the other down.
I hope to have a program available by next year to automate multi-camera
operation. The current programs on offer don't do what I
want to do- at least not for Pentax cameras. I want to write
a simple spreadsheet table of elapsed time, and shutter speed
for an exposure at that time. The program will look up this
table and control the cameras shutter speed, trip the shutter
and write to a nice fast SD card. The software will be available
free to the SE community & it may also work on some Nikon
cameras that have a similar bus to the Pentax.
See you next year in Shanghai!
Joseph Cali
