City of the stars
[15] C109 (NGC 3195) the last object in the Caldwell catalogue. It is a planetary nebula.
This image is from the Hubble Space Telescope.
[16] Star clusters and nebulosity abound in the North America Nebula (NGC 7000) located
in Cygnus, the Swan.
[17] A chance stellar alignment produces an asterism (unofficially recognised pattern)
that, in this case, resembles a coathanger (Brocchi’s Cluster).
1415 1617results. Once again, flats also contain random noise so take a number of
them and average them together to produce a "master flat".
Alternative methods to take flat fields include building your own light box
or using an electroluminescent panel which can be held over the front of
the scope to give a uniform plane of illumination. It’s very important that the
camera’s position relative to the telescope is not changed between taking
the light frames and the flats. If this does occur, the flats will be useless. A
further type of calibration image is the bias frame. This is quite easy to take
and simply requires you to put the lens cap on the telescope and take the
shortest exposure possible.
3) Once all of the calibration files have been successfully captured, the next
step is to apply them. There are various commercial applications which
can do this automatically as long as you tell the program which file is
which. Alternatively, there are freeware options available which will do
a similar job. One popular freeware application to perform all calibration
steps automatically as well as assembling the final calibrated files into a
finished image is DeepSkyStacker (http://deepskystacker.free.fr/english/
index.html).
4) Once you’ve created the end result, you may feel a little cheated as it
may not look that great to start with. This is where the final "image
processing" stage is applied and is the one that will either make or break
the final image. There are many dedicated programs available to handle
astronomical image processing and much of the subject is beyond the
scope of this book. A layer based graphics program such as PhotoShop,