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© Baader Planetarium GmbH | 2021
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Manual: SunDancer II
Calibrating the Filter and
Settings of the Temperature Control Box
Setting the Temperature
The target temperature of the filter and thus the position of the central wave length of
the transmission window can be adjusted via the temperature control box. This serves
on the one hand to calibrate the filter to your individual system (see the following
chapter "Filter calibration"), and on the other hand for finetuning to observe the red
or the blue wing of the H-alpha line. For observations in the blue wing, you can also
simply use the micrometer screw so that the filter is set exactly to the H-alpha line.
To change the target temperature, proceed as follows:
1. Wait until the filter has reached its stable operating temperature and displays the
numerical value "0".
2. Press UP or DOWN once to enter the programming mode. The display "0.0" fla-
shes. Now press UP to increase the temperature or DOWN to decrease it. If no key
is pressed for a few seconds, the new setpoint is accepted.
3. The value can be changed by a maximum of 10.0 degrees. A change of 10.0 de-
grees shifts the central wavelength by about 1 angstrom (1Å, equals 0.1 nm).
4. An increase in the setpoint value corresponds to a shift of the central wavelength
into the longer focal length, i.e. the red region of the spectrum. A decrease shifts it
accordingly to the shorter wavelengths, or the blue range of the spectrum. In the
blue wing of the H-alpha band, they can observe the rapid, high-energy changes on
the solar disk.
The new value is stored even if you disconnect the power supply. The display always
refers to the factory preset target temperature.
Note:
The filter temperature is influenced by the incident solar heat. If the filter is not
pointed at the sun for some time, the transmission line shifts into the blue range of the
spectrum. As soon as the telescope is pointed at the sun again, the heating compen-
sates for the additional solar energy, and after 30 to 60 seconds it is back to its original
wavelength.
Note:
For best imaging and to avoid reflections, the filter should not be tilted. The
micrometer screw is used for
quick
observations of Doppler effects; the H-alpha line
should be adjusted via the temperature.
Calibrating the Filter
The SunDancer II has been calibrated at the factory and should give the best image
when the micrometer screw has been turned clockwise as far as it will go without
applying force and the heater has reached the preset target temperature, so that the
temperature difference display is also at "0". After about three to five minutes of solar
observation, the filter has reached temperature equilibrium and you can assess its
performance.
For optimal performance on your particular system, you should calibrate the filter
to compensate for differences in aperture ratio, energy rejection filter and more. This
should require only small corrections to the factory setting, which was set at an effecti-
ve focal ratio of f/30. To do this:
1. Turn the micrometer screw clockwise as far as it will go (without applying force).
2. Set the temperature control box to a value of -5.0 as described above in the chap-
ter "Setting the temperature". Give the filter 3 to 5 minutes to stabilise and observe
the sun exactly in the centre of the image of the filter. You should now see it in the
blue wing of the H-alpha line.
3. Increase the target temperature by 1.0 degree (corresponding to 0.1 Å) and give the
filter a couple of minutes to stabilise again.
4. Increase the target temperature until you see the sun with the best contrast. The
solar disk is then darkest and you have centred the filter exactly on the H-alpha line.
Increasing the target temperature moves the filter to the red wing, decreasing it
moves it to the blue wing.
A change of more than ±10 degrees is not advisable .
Increasing the temperature too much can destroy the filter .
Tilting the Filter
With the micrometer screw, you can tilt the filter up to 3° off the optical axis to quickly
shift the central wavelength into the blue wing. If the image improves when you tilt the
filter, this may have two causes:
1. The filter line is in the red wing of the H-alpha line at target temperature.
2. The micrometer allows the filter to be tilted past the neutral position.
The set point of the target temperature should be adjusted to give the best image
when the micrometer screw is turned gently clockwise to the stop. Then you can tilt
the filter towards shorter waves, into the blue wing of the H-alpha band, by turning the
micrometer screw back. In the blue wing, you can better observe rapid, high-energy
changes on the sun.
Troubleshooting
If the filter does not deliver the expected contrast, it is usually because it is not aligned
exactly to the optical axis. Even with a tilt of 0.5°, the filter can no longer work as desi-
red. A tilt can be compensated for to a small extent by increasing the target tempera-
ture, but this also increases its half-value width.
In case of tilting, first check whether your focuser tube is correctly adjusted or whe-
ther it has play and gives way under load. Simple clamping screws on the focuser or
zenith mirror can also cause tilting.
