Handbook for the SX Midi Filter Wheel - Issue 1, January 2019
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wheel and operating it when the camera software does not support the SX wheel
protocols.
Connecting up the wheel:
USB control:
If you are using USB control, then the only connection required is that between the
USB port on the wheel and a USB output on your computer. You may, of course, use
a USB hub, if necessary – a powered hub is recommended to ensure that the wheel
motor has sufficient torque to operate reliably. When the wheel is first connected,
Windows will display a message about ‘New hardware found’ followed by ‘SX filter
wheel’. Shortly afterwards, the wheel will rotate once or twice as it calibrates and
determines the number of filter positions available. It is now in position 1 and ready
to use. If the wheel motor ‘pulses’ in a cyclic fashion and doesn’t stop, then the
calibration has failed and you need to check that the USB connection is good and
that the carousel can move freely.
Using the OAG pick-off:
The OAG pick-off assembly is designed to be used with an SX Lodestar or Ultrastar
guide camera, but other types may be employed if they have a 'C' mount (1 inch)
threaded input collar. Fit the guide camera onto the C mount ring and slide the ring
onto the OAG tube. Use the small lock screw to fix it about halfway down the tube.
Loosen the large lock screw and slide the prism tube until the prism is roughly
tangential with the edge of the filter aperture. With this assembly attached to the
'scope and the main camera operating, focus the main camera to give a sharp image.
Now switch to the guide camera images and adjust the C mount ring along the pick-
off tube until the guide camera is focused on any visible stars in the guider field. If
you cannot see many stars, or they are badly distorted, slide the prism assembly a
little further in, but be careful not to 'shadow' the main camera field.
Filter Wheel maintenance:
Very little maintenance is required and is limited to occasionally cleaning the
carousel and drive wheel to remove any dirt or grease deposits that might cause
slippage. A few drops of alcohol on a soft cloth will clean the surfaces and fix any
drive problems. Under very cold conditions, residual moisture might cause the
central bearing to freeze to the brass shaft. This can be alleviated by applying a
single drop of light oil to the shaft to repel moisture.
