|My previous location and equipment.
We used to live in Miri, at 04 deg 20' N, 114 deg E. This was where
all the webcam images were taken
Being close to the equator, the climate is tropical with
temperatures in the range 23 - 91 deg C (74 - 89 F). We get lots of
rain - annual rainfall is 111 inches a year! There are, on average,
166 days with rain in a year, and the sky is not often without cloud, given
the high humidity. Here's a chart showing the temperature and dew
point on a typical day.
Relative humidity climbs through the evening and the dew
point is usually reached at around midnight. On a cloudless evening, I
will start imaging at around 8 pm, but by midnight the air at altitude will
hit dew point and the sky is then effectively shut for the night!
Given that for half of each month the moon is out and the
sky then is too bright for imaging Deep Sky Objects, I usually get on
average 2-3 imaging nights a month.
My telescope is an 8" f/5 Newtonian
reflector, which I bought in late 2001 from
BTOW in Perth, Western Australia.
It is a Skywatcher, which is made in China, I believe by Synta (??). I
am quite happy with the quality of the scope, even under the demands of CCD
imaging, but I don't really have a basis for comparison, as this is my first
I image exclusively from my balcony, which has a good
view of the eastern sky. Being near the equator I am able to view both
the northern and southern skies up to about +-75 deg Dec.
The focuser is pretty basic, which means that the fine adjustments needed
for imaging need to be made with a very fine touch indeed. On the plus
side, there is next to no image shift as the telescope is focused.
The focuser is shown below with the supplied 2" to 1.25" eyepiece adapter.
The mount came with the telescope and is a
Skywatcher EQ5 with Dual Axis drive. There is a basic hand controller,
seen here next to the computer.
I am definite that the mount is not really up to imaging. Its
periodic tracking error is about +- 25 arcsecs. This is high, but
what is worse is that the tracking jumps suddenly at parts of the cycle. As a
result I am only able to do individual exposures of only 25s. Even
with these short exposures, I normally have to discard 70% of the frames due to
The mounts stability in wind is also insufficient. It's lucky that
most nights here are quite still. Even a slight breeze renders imaging
Balancing the mount
I usually arrange the
counterweights on the mount such that there is a slight weight opposing the
direction of tracking. This keeps an even pressure on the drive train
and helps tracking accuracy.
From my balcony there is a clear view of the east, but
the western sky is obstructed by my house. So I tend to start imaging
when the target is about 30 deg above the horizon. In this position,
in order to keep weight on the drives, I usually position the telescope tube
in the holding rings so that the upper part (the aperture) is 'heavier'.
The camera is a SAC7B from
SAC Imaging. This
is a commercially built webcam conversion. Being a webcam, image depth
is only 8 bits, as opposed to the 12 or 16 bits normally used by
conventional astronomical CCD cameras.
The camera has Peltier (thermo-electric) cooling, which should cool the
CCD to 30 deg C below ambient. However I do all my imaging with the
camera uncooled. This is because in the humid conditions here, even
slight cooling causes condensation on the CCD window. The white
connector is for the Peltier - usually unused.
Fortunately the camera has low, repeatable, dark-current, the noise from
which can be effectively removed by subtracting dark frames.
with the 1.25" eyepiece adaptor attached is shown here, with the 2" to 1.25"
adaptor removed from the telescope.
|Attaching the camera to the telescope
attach the camera directly to the telescope by removing the eyepiece
adaptor from the camera as well as the 2" focuser attachment (shown right),
then screwing the camera to the 2" focuser attachment. This is then
attached back to the focuser assembly (below). Notice the marks I have made
on the focuser barrel to indicate the approximate positions of focus.
The inner marks - on the barrel just outside the black bit - indicates prime
focus, while the other mark is used when imaging with a Barlow lens.
Because I operate the telescope and camera
from a desktop computer located in the room adjoining the balcony, I have to
run cables from the telescope to the room.
There are 3 sets of cables
(picture at right). The first (centre), runs from the hand controller
to the mount and controls the RA and Dec drives. I made these up from
two phone cables bound together with electrical tape and wound onto a
fishing line reel.
The USB extension cable (left) came with the SAC7B.
The image is transferred down this cable.
The exposure control cable
(right) for the camera is a normal phone extension cable and is connected to
the computer via a phone-jack to parallel port adaptor (included with the
Below is my setup for imaging with all cables connected.
The mount and drive
originally came with a battery pack that took 4 'D' size batteries.
Since I run the mount for long periods (4-5 hours per imaging session) these
batteries would quickly run out. Instead I use a 6V AC-DC power supply
that originally ran a small cassette player to run the mount. This
plugs into a power board under the computer table.
Ironing board and golf umbrella
Serious astrophotography accessories! Right in
front of my house is a bright halogen streetlamp. I use the umbrella,
held by the ironing board against the balcony railing, to shade the aperture
of the telescope from this light.
I have made a cheap and simple
infrared filter from 2 pieces of exposed and developed colour print film.
More information can be found on my Infrared