imaging is not fulfilling. I remember
the first time I managed to capture
Saturn. It was the only planet in the
sky at the time and I was impressed
with the tiny image showing the
planet and rings in less than 150x100
pixels. There was a strong feeling of
accomplishment having captured
and processed the image with my
modified computer web camera.
Having decided that this was
something I really wanted to do I
then purchased a 5MP Celestron
NexImage 5 expecting to take
much better images as the sensor
was much larger 5MP compared to
0.3MP. I was wrong! All I managed
to achieve was to get more dark sky
in the image (explained later). The
camera did have other benefits so
I was not complaining. I also found
that it was impossible to video at
5MP and process the video. The
frame rate drops dramatically and
the files that are large at lower
resolutions suddenly become huge!
Jupiter and moons captured with Celestron
NexImage 5. Credit: Mike Barrett
Getting started
Once you have your telescope
pointing in roughly the right direction
with all the connections made you
will probably find it quite difficult to
locate the planet that you are trying
to image. This is most likely because
the telescope is not at the correct
focus point. When the focus is a long
way out you will not be able to see
anything on the preview. So when
first starting out it is best to pick a
large object like the Moon. The Moon
is so bright that even with an out of
focus telescope you will still see a
silver disk. If you are trying to locate
Jupiter or Saturn and you are not
close to focus then you will struggle.
Having located the moon the first
24
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Comparison of the 1.2MP QHY5L-II and 5MP NexImage sensors. Credit: Mike Barrett
thing to do is to focus the telescope
with the webcam attached to the
eyepiece. Obviously the easiest way
to do this is with the computer very
close to the telescope. This will allow
you to turn the focusing knob at the
same time as viewing the image on
the screen. At this time it is probably
best for the camera to be set to Auto
Gain and Auto Exposure. When you
have achieved focus make a note of
roughly where the focuser is on the
telescope. This will enable you to get
the setup focused faster next time.
If you are imaging the Moon then
you are ready to go. If you are trying
to capture one of the planets you
now need to point the telescope to
the planet (Jupiter is the easiest to
start with) and then focus again. The
fact that you have already focused
on the moon will mean that the focus
will be almost right for the planet.
With a nice sharp image on the
screen you will see that the target
object appears to wobble a bit,
sometimes quite a lot. This is the
effect of the turbulent atmosphere
and sometimes the wind. If people
are walking around your setup then
this can also transmit vibrations to
the telescope. Now you can s YB