The
solar analemma
Text
and pictures by Anthony AYIOMAMITIS
Photographic
Notes (II)
With
the critical "theoretical" issues now out of the way, it
was time to address the type of film to use in conjunction with my
solar filter material and camera lens. Since the Baader solar filter
material is rated at ND-5, software calculations suggested an
exposure of 1/500th sec when stopped at f/11 using
an ISO 200 color
film emulsion (e.g. Fuji Super HQ 200).
In
order to compensate for days with potential haze or cloud cover or
during the winter when the sun is lower and not as bright due to
atmospheric effects, I decided to purposely overexpose by three
stops and image at 1/60th sec. A 60 mm x 60 mm square of the Baader
solar material was cut and inserted between the filter threads of
the wide angle lens and its 52 mm UV filter; the filter was then
threaded into the lens carefully so as not to tear the filter
material. A test roll was shot to confirm the absence of any light
leaks due to tearing or shearing as well as the suitability of the
selected f/stop and exposure.
To
download : Exposure
Calculator
A
software from Michael A. Covington
The final consideration is, of course, the stability of the
camera and its mount. Rather than risk the accidental bumping of a
tripod over the next twelve months (at least 43 such opportunities
for an accidental bump), I constructed a two-part mount for my Canon
A-1. The first was made of laminate material and permanently held
firmly in place using carpenter's clamps (everything was covered
with very durable material - used for 20 kg bags of dry dog food -
for protection from rain which could soak and expand my laminate
material and, consequently, destroy my permanent and fixed
direction) (see Figure 2).
The second mount was permanently attached
to my camera - using silicon between the back of the camera and the
vertical support behind it as well as the camera base plate and
mount - with the camera and its permanent support sliding very
tightly into the permanent laminate base (potential cold weather and
rain during the winter season did not permit for the camera to be
permanently left outside) (see also Figure 2). Also, a one-inch
diameter whole was drilled into the permanent camera support for the
Canon AE-1 camera bodies below the film rewind button so that the
unorthodox method described below for taking multi-exposures with
these cameras could be realized. Every four months, additional
silicone material was applied to reinforce the bond between camera
body and mount.
Here
are the reflex cameras used and their wood support constitued of
two parts :
The tripping of the shutter release cable at precisely
06:00:00 UT was preceded by my pinging to a time server operated by
the US National Institute of Standards and Technology (NIST) using
the free software "Atomic
Clock Sync V2.0" ten minutes prior to the proposed
imaging for the calibration of my cellular phone to the atomic
time-scale operated by NIST so as to be accurate to within +0.5
seconds (even a deviation of a few seconds, especially around the
late summer, will show up as a significant "outlier" in
the final analemma).
the time can also be check listening to dedicated shortwaves
frequencies.
Connect
you to Time Servers:
BIPM
(France) - NIST
(USA) - Time in any city - ClockLink
First
Marathon Attempt
With a shutter release cable hooked up and a fresh battery
inserted into my Canon A-1, the first of eleven analemmas with
imaging at 06:00:00 UT was under way starting at the summer
solstice (Jun 21/01) and scheduled for completion in early June,
2002.
In corresponding with Dennis di Cicco a couple of weeks
following the start of the first analemma, I was delighted to learn
that a perfectly vertical analemma on the meridian, corresponding to
imaging at 10:28:16UT, had yet to be produced. As I was already
slightly past the summer solstice, I had to determine the time that
Mars one evening would be at precisely 180° azimuth so as to
calibrate the perfect placement of the camera and its mount with
respect to azimuth and, thereby, avoid any possible distortion
effects from my wide-angle lens and to also ensure that the
introduction of a composite image upon completion would be an easy
task. Once this was completed, yet another analemma was immediately
initiated using my second Canon A-1 camera. Of course, greed and
determination got the better part of me and a further four analemmas
(07:00:00 to 10:00:00 UT) were started very shortly thereafter as
well since my ultimate objective was to produce a complete set of
analemmas (one-hour intervals between 06:00:00 and 15:00:00 UT and
at 10:28:16 UT for the special meridian case).
|
The
analemma of 6h UT over Tholos, Ancient Delphi. |
With six analemmas in progress by late summer of 2001 and,
regrettably, another five remaining as outstanding items literally
made for some sleepless nights. The acquisition of yet additional
Canon camera gear during the days and weeks that were to follow had
set me in motion towards a very special and productive 2002 as I was
under way in producing eleven analemmas representing the complete
gamut from sunrise to sunset.
With the passage of time, potential obstacles seemed to be
nothing but minor nuances. Two strong earthquakes (Jul 26/01: 5.7
Richter, Oct /01: 5.2 Richter) did not impact any of my permanent
mounts or analemmas in progress. Uncharacteristic bad weather
surfaced on a large and fatal scale in early Nov/2001 when between
planned exposure dates severely adverse weather over four
consecutive days led to loss of life and hundreds of flooded homes
in the immediate area due to such heavy rainfall not seen for many
decades. Being physically situated on the side of a mountain not
only helped me bypass both personal and property damage but enabled
me to keep focused on the eleven analemmas in progress.
However, it
is at this time that I realized that, in retrospect, I should have
constructed my permanent mounts of metal and not laminated wood
material since exposure to these heavy rains, in spite of the
aggressive protection in place, did make the previously tight fit
with the camera mounts now even more tighter and necessitated the
forceful pushing of the camera mount into the permanent mount for
two of the cameras involved. Also, analysis of the associated
ephemeris during these four days suggested that the impact would
have been negligible anyway even if I were to trip the shutter at +2
or +3 days later than planned since the daily movement of the sun
across the sky in November is relatively "slow".
Nevertheless, I would lose during this four-day storm my opportunity
to take a multi-exposure of the partially obstructed solar disk for
the latest analemma (15:00:00 UT) which was to serve as a partial
replacement for the six exposures which would ultimately be
forfeited around both sides of the winter apex due to a physical
obstruction (a mountain again) that could not be circumvented.
The weather conditions were potentially the greatest factor
in causing grief and havoc as I explain in the last page.
|
The
analemma of 7h UT over Apollo's temple, in the ancient Corinth. |
To this end, I religiously checked the
weather conditions a day prior to my proposed shooting and did so
sufficiently early during the day so as to possibly advance my
schedule by one day in the event rains and/or heavy clouds were
predicted for the scheduled day as well as the day thereafter, for I
was very determined not to deviate from my proposed shooting
sequence by more than + 1 day due to the desired symmetry (vertically
and horizontally) in the completed analemmas (sole exception is the
crossover point where absolutely no deviation is possible).
With my first two analemmas (06:00:00
UT and
10:28:16 UT) about
50% completed, I would for the first time forcefully deviate from
this sacred wish in early December, 2001 when my scheduled exposure
was not only missed for that day but daily heavy cloud conditions
and/or rain - the worst rainfall for December in over a decade and
greatest snowfall in over 39 years - did not permit for any
supplementary imaging for the two weeks that were to follow and,
consequently, a much undesirable "gap" immediately before
the winter apex was to be a common characteristic and trademark for
all of these analemmas upon completion (they reflect the strong anger
of the Greek gods!).
The more and more I thought about this missed multi-exposure,
the more aggravating the whole situation became for the simple
reason that I wanted a perfect set of analemmas from sunrise to
sunset. With daily weather predictions for my next scheduled
multi-exposure, the winter solstice on Dec 21/01, consistently
showing heavily clouded skies, I began to entertain the unthinkable.
Upon confirming the presence of overcast skies on the early morning
of winter solstice, I formally executed the fateful and humbling
decision to restart all analemmas and forego the well over 100 total
multi-exposures taken to-date. To this end, in early Jan/2002 and
with perfect overhead skies, I restarted all eleven analemmas so as
to have a potential time series spanning a single calendar year,
something that is not characteristic of any of the successful
analemmas to-date (the analemma by HJP Arnold and described by di
Cicco was the closest to have been taken during a single calendar
year as it ran from Jan/88 to Jan/89).
Although very disappointed at
turning my back on so much work and time, delaying the appearance of
completed analemmas by six months (assuming no similar future
compromising events), risking the first appearance of a perfectly
vertical analemma on the meridian by someone else and rolling the
dice again for the next twelve months, this decision had the benefit
of permitting all eleven analemmas to have a common start and end
point as well as representing the sun's movement over the local
skies precisely during one calendar year. I purposely refrained from
continuing the existing multi-exposures and simply waiting for Dec
3/02 and Dec 21/02 where I could hopefully reshoot the missed
exposures for those days as the multi-exposures would then not have
been over twelve consecutive months. Similarly, purposely skipping
the Jan 12/02 exposure so as to re-establish the horizontal symmetry
but now with two less total exposures per analemma may seem like a
suitable fix but is also not a viable option since the vertical
symmetry had already been adversely impacted by the Dec 03/01 missed
exposure and was beyond repair.
Next
chapter
Second
Marathon Attempt
|