Handbook for the TRIUS PRO 694 Issue 19th April 2019
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Although the star will also suffer from blurring, the eye can more easily gauge when
the most compact blur has been achieved!
You could begin by imaging lunar craters, or the planets, Jupiter, Saturn or Mars. The
rapid variations of seeing which accompany planetary imaging, will ruin the
definition of about 95% of your images and so I recommend setting the camera to
run in ‘Autosave’ mode. This will automatically take a sequence of images and save
them with sequential file names in your ‘Autosave’ directory. Dozens of images will
be saved, but only one or two will be satisfactory for further processing. The
‘Subframe’ mode of Starlight Vision may be found useful for limiting the wasted area
and reducing the download time of small planetary images.
To start the Autosave process, call up the Exposure tab and select the ‘Actions and
Files’ button. You will see a default file name with a numerical suffix, and various
options for the image save folders - set an appropriate file name and image save
folder location. Once done, you can go to either the ‘Continuous’ checkbox for
automatic saving of every frame, or you can set a number of exposures in the
‘Number’ box. The ‘Autosave’ option should then be checked and you are ready to
start. Set an exposure time and press ‘Start Exposure’ - your frames will now be
saved to your folder of choice. Make sure that you uncheck ‘Autosave’ when
finished, or you will save every image that you take!
The exposure time needed for good planetary images is such that the image
histogram has a peak value at around 40,000 and does not extend much above that
value (Ignore the major peak near zero, due to the dark background). If you use too
short an exposure time, the image noise level will be increased, and if too long a
time is used you will saturate the highlights and cause unresolved white patches on
the image highlights. With the recommended focal length, Jupiter and Mars will both
need an exposure time of between 0.1 and 1 seconds and Saturn will need between
0.5 and 2 seconds.
Processing a planetary image:
Planetary images have one major advantage over deep sky images, when you come
to process them – they are MUCH brighter, with a correspondingly better signal to
noise ratio. This means that aggressive sharpening filters may be used without
making the result look very noisy and so some of the effects of poor seeing can be
neutralised.
As with deep-sky images, it is advantageous to stack planetary images together to
improve the signal to noise ratio. In this case, the ‘averaging’ option should always
be used, or the result is likely to exceed the dynamic range of the software and
saturate the highlights. Aligning the images is always something of a problem, as
there are rarely any stars to use when imaging the planets, but Jupiter’s satellites
can be useful reference points. Otherwise, you will have to find a well-defined
feature on the planet, or estimate where the centre of the disk is located. Some
