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8 Imaging
aware of how long it will take to run and be at the telescope before it finishes.
Otherwise, the instrument might stand idle when it could be being used.
7. Although not entirely necessary, many amateur astronomers like to take a clear
frame in addition to the three coloured filters. The clear is used to form a luminance frame in the modified version of the standard RGB colour images, known
as an LRGB. LRGB images tend to have a better definition of fine structure, but
not all imaging software can produce LRGB images, although MaxImDL can.
8.7.5 Shutdown
Once you have all your light frames, do not forget to take your calibration frames if
you haven’t already. Make sure you have everything in your lab book that you need,
including the details of the telescope and the time you finished imaging.
It is likely that your instrument has a specific shutdown procedure, which you
should know. If you do not, please check with a member of the observatory staff.
In general, this procedure requires parking the telescope, which puts the instrument
in a known position so that when it is restarted, it knows where it is pointing. The
dome will need closing, and if it is a tracking dome, it may also need parking. You
should shut down the camera and its cooler and turn on any ancillary equipment
that you might have turned off, and vice versa. For example, some observatories use
dehumidifiers to protect the optics.
8.7.6 Post-imaging
After taking your images, you will need to produce your science frames. In order to
do this, you will need to subtract the correct dark frame from each of your flats and
then normalise the flat.
1. Subtract the dark frames from your light frames.
2. Divide the result by the flat to produce a science frame.
Note that since the dark frame includes a bias, it is not strictly necessary to have
bias frames. However, if you do not have a dark frame with the correct exposure
time for some reason and you need to make one by scaling another dark frame,
you will need to subtract the bias first, as it doesn’t scale, and then add it back
after the scaling. As bias frames are so quick and easy to take and can be useful, I
suggest you always take them even if in the end you do not use them. The process
of making science frames is discussed in more detail in Sect. 7 in Chap. 9.
3. If you have multiple images of each band, you should stack these to improve the
signal-to-noise ratio. However, be aware that when you stack frames, the nature
of the stack can destroy the scientific usefulness of the data. For the Messier
marathon, this is not an issue, as you are attempting just to produce an image, but
8 Imaging
aware of how long it will take to run and be at the telescope before it finishes.
Otherwise, the instrument might stand idle when it could be being used.
7. Although not entirely necessary, many amateur astronomers like to take a clear
frame in addition to the three coloured filters. The clear is used to form a luminance frame in the modified version of the standard RGB colour images, known
as an LRGB. LRGB images tend to have a better definition of fine structure, but
not all imaging software can produce LRGB images, although MaxImDL can.
8.7.5 Shutdown
Once you have all your light frames, do not forget to take your calibration frames if
you haven’t already. Make sure you have everything in your lab book that you need,
including the details of the telescope and the time you finished imaging.
It is likely that your instrument has a specific shutdown procedure, which you
should know. If you do not, please check with a member of the observatory staff.
In general, this procedure requires parking the telescope, which puts the instrument
in a known position so that when it is restarted, it knows where it is pointing. The
dome will need closing, and if it is a tracking dome, it may also need parking. You
should shut down the camera and its cooler and turn on any ancillary equipment
that you might have turned off, and vice versa. For example, some observatories use
dehumidifiers to protect the optics.
8.7.6 Post-imaging
After taking your images, you will need to produce your science frames. In order to
do this, you will need to subtract the correct dark frame from each of your flats and
then normalise the flat.
1. Subtract the dark frames from your light frames.
2. Divide the result by the flat to produce a science frame.
Note that since the dark frame includes a bias, it is not strictly necessary to have
bias frames. However, if you do not have a dark frame with the correct exposure
time for some reason and you need to make one by scaling another dark frame,
you will need to subtract the bias first, as it doesn’t scale, and then add it back
after the scaling. As bias frames are so quick and easy to take and can be useful, I
suggest you always take them even if in the end you do not use them. The process
of making science frames is discussed in more detail in Sect. 7 in Chap. 9.
3. If you have multiple images of each band, you should stack these to improve the
signal-to-noise ratio. However, be aware that when you stack frames, the nature
of the stack can destroy the scientific usefulness of the data. For the Messier
marathon, this is not an issue, as you are attempting just to produce an image, but