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"The Universe on Video"
by Rod Mollise Published in May-June 1997 Skywatch Journal Mobile Astronomical Society, Mobile Alabama (article reproduced with author's permission) |
Sitting around one afternoon last July,
I started thinking about
video astronomy again. I think what started me
reconsidering this subject was
the wonderful apparition of Jupiter. Last Summer,
the planet was huge,
beautiful and highly detailed in my 12.5" Dob.
How could I make some images
of this monster planet? Video hadn't worked very
well before but... How about
the camcorder? I have access to a fairly high
grade camcorder, a Sony CCD
F-34, which features a very sharp lens, adjustable
shutter speeds (this is a
good feature--instead of just having an automatic
setting, the camera allows
you to manually select shutter speeds from 1/30
to 1/1000 second), and a
number of other ‘pro' features. Of course, as
is the case with most
camcorders, the lens isn't removable, so there
was no way to use it in an
eyepiece projection setup or to readily mount
the camera on the scope (it's
rather heavy to mount on a scope anyway). But
then I thought of the afocal
method of astrophotography. In this setup, the
lens stays on the camera,
which take the place of your eye at the eyepiece.
With this method, it's
quite easy to handhold the camera and, for example,
take nice, sharp Moon
pictures. Unlike eyepiece projection, the film
plane of the camera doesn't
have to remain parallel to the image plane of
the telescope during afocal
astrophotography. I've used this technique
to make some impressive lunar
photos with Dobsonians. Since I wouldn't be mounting
the camera on the
telescope, I thought I'd experiment with the
12" Dobsonian to start with,
since it just naturally delivers a more detailed,
brighter image of Jupiter
than the 8" SCT.
With Jupiter in the field of a 26mm Plossl
on the 12" I started
making my first videotape of the planet. One
thing that I discovered right
away was that the viewfinders on modern cameras
are good enough to make
focusing a fairly easy. Following the procedure
that I use with 35mm afocal
photography, I set the camera lens to its closest
focus (make sure the camera
you use has a means of turning off automatic
focus) and focused the image
with the telescope's focuser. That first evening's
session revealed that it
was quite practical to use a Dob for video astrophotography--a
drive really
isn't needed. It was easy to hand hold the camera
and track the image of the
planet as it crossed the scope's field of view,
keeping it in the center of
the frame. As the image of the planet reached
the edge of the eyepiece field,
I would stop the camera, reposition the telescope,
put the image back in the
center of the camera's viewfinder and start the
camera again. Since most
modern camcorders have ‘flying erase heads' which
eliminate ‘glitches' on the
tape from the camera being stopped and started,
you can hardly tell, looking
at the finished tapes, where ‘takes' end and
begin--the planet just seems to
stay smack in the middle of the screen. After
shooting about 15 minutes of
tape, I hurried inside to see what I had accomplished
(while I could tell
that I was in focus, the camera's small black
and white viewfinder made it
difficult to determine how much detail I was
recording).
To say that I was pleased with my efforts
would be an understatement!
Jupiter was fairly large on TV, (about
the size of a quarter), showed some
banding, some hints of color, and even a couple
of moons from his retinue of
satellites! Happy as I was, though, I noticed
a problem: the planet was
heavily overexposed (I had been really worried
about there being enough light
to record anything!). The next night I decided
to try a range of eyepiece,
zoom, and filter combinations to see what worked
best.
What I discovered amazed me! By using a
7mm eyepiece and extending
the zoom to its maximum focal length, I was able
to obtain an image that was
not only huge (about 6" across on a 25" monitor!),
but one which was also
highly detailed and which showed some of Jupiter's
subtle colors! I also had
some luck using slightly lower magnifications
(12mm eyepiece) in concert with
colored filters. A blue 80A filter revealed a
wealth of detail!
I found-out something else rather quickly,
too. By repeatedly viewing
my Jupiter tapes, I was able to see more detail
than I was often able to
detect at the eyepiece! There are two reasons
for this. First, on video the
image is quite large--even at 300x or more, the
image at the eyepiece is
still relatively small. Second, when I find a
section of tape where the
seeing was unusually good, I can rewind and watch
the sequence many times
allowing me to see all that there is to see.
Last summer, I was routinely
able to see the Great Red Spot (I even detected
detail within the red spot
occasionally), details in the cloud bands, shadow
transits of satellites, and
more. When the seeing is steady I can even resolve
the Galilean moons as
disks!
I did decide to try one last modification
to my ‘procedure.' Perhaps
I needed to mount the camera on a tripod? Hand-holding
it just seemed too
easy! I was able get some images of Jupiter with
the camera mounted on a
tripod, but it soon became evident that this
was not the way to go when using
a Dob. With the camera mounted on a tripod, I
lost the ability to easily
‘track' the planet--it just zipped across the
frame. At high magnifications
(and the final result in video astrophotography
is usually an image with an
equivalent magnification in the THOUSANDS) moving
the SCOPE to ‘track' the
planet is hopeless. I went back to hand-holding
the camera, and have been
happy with this method ever since.
What else have I been able to Image?
The Moon: particularly impressive are some shots
I have of lunar features
like Copernicus, Plato, Clavius, etc. Using the
7mm eyepiece/max zoom
combination I used on Jupiter, I'm able to make
the larger craters literally
fill the screen of a 25" monitor! I'm also able
to detect color on the lunar
landscape.
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The photo at left shows an afocal setup using
a hand held camcorder to record images through the telescope eyepiece.
The photo of Copernicus at right demonstrates the quality of image that can be obtained in this manner. Photos courtesy of Rod Mollise |
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Saturn: Saturn is dimmer and smaller than Jupiter,
and is, therefore, more
difficult to image than Jupiter, but I was able
to record quite a bit of
cloud banding during the past apparition. I was
also even able to detect
Cassini's division though the rings were barely
‘open' at the time!
.
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| Telescope was the 12.5" dob with a 20mm Plossl and 2X Barlow, Sony 8mm Camcorder CCD F-34, image processing with Paint Shop Pro. |
Comet Hale-Bopp: I've been told that video cameras
usually can't record much
of anything at all when it comes to nebulous/extended
objects (for this you
usually need an integrating camera--a ‘CCD camera'),
but the comet was SO
BRIGHT that I decided that it was worth a try
after all. Surprise! I got some
very pleasing footage of the comet, both at the
eyepiece and using the
camera's telephoto lens only. On the ‘through
the eyepiece' sequences, the
comet's nucleus is very bright, and it is possible
to detect the ‘waves,'
‘hoods,' and clumps of matter coming off the
comet! I got one very nice shot
of the comet with the camera's lens alone. Initially,
only the comet's bright
nucleus and a decent extent of tail are visible.
As the sky brightens with
the coming of dawn, though, the comet becomes
framed by bare winter branches
in the foreground.
What next? I'd like to do more as far as
preserving some of my images
as ‘hard copy.' I've had fairly good results
by photographing the monitor
screen with a 35mm camera, but the obvious solution
is to obtain a video
capture device which allows the image to be read
into a computer and
processed. I'm currently considering the ‘Snappy'
video board. The price
seems fairly reasonable, and I'm hearing that
the results are excellent. I'm
also wondering whether a higher- resolution camera
would be a help. Some
modern CCD-type surveillance cameras are available
at <$400.00, and most have
resolutions and sensitivity far better than the
average camcorder. And how
about a Dob Driver or equatorial platform for
the telescope? Might this make
filming a little easier?
Why not give video astrophotography a try?
All you need is a
camcorder (any camcorder), an eyepiece, a telescope
(I've had good results
with scopes as small as my 6"), and a desire
to record the beauty and majesty
of the heavens! If you doattempt it, please share
your results with me! If
you'd like to see what I've achieved with my
simple equipment, get me a blank
tape and I'll make you a copy of my ‘best of"
film!
--Rod
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