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Calibrating the Filter
The SolarSpectrum filter are calibrated at the factory for f/30 and should give the best
image when the display of the temperature difference is at "0", or if actual and target
temperature are the same. 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. 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 the sun in
the blue wing of the H-alpha line.
2. Increase the target temperature by 1.0 degree (corresponding to 0.1 Å) and give the
filter a couple of minutes to stabilise again.
3. 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 .
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
star diagonal can also cause tilting.
