Equatorially aligning means ensuring that the camera is rotated appropriately with respect to the focusser mechanism so that its imaging frame is aligned exactly east-west and north-south.. This should only be necessary if the camera has been moved between imaging sessions. It is important to do this before finally focusing the camera before imaging because rotating the camera inevitably means very slightly changing its distance from the primary mirror and therefore affecting its focus setting.
The camera is joined to the filter wheel by a T-thread. The filter wheel is joined to 10mm + 7mm spacer rings and they in turn are joined to the focusser housing, all using T-threads. The camera, filter wheel and spacer rings are all rotated as a single unit and they are locked against the focusser housing by a locking collar. Thus to rotate the camera it is necessary to unscrew the locking collar a bit, rotate the camera, etc. and then re-lock the collar.
To make sure that the camera is properly equatorially aligned one of two methods can be used :
- In the more accurate method the handbox is used to move the mount so that a star is placed on, or close to, the central reticle line in Artemis Capture. The mount is then slewed eastwards and westwards. If the star does not exactly track along, or parallel to, the reticle's central line, adjust the rotation of the camera and repeat until it does.
- A method that is almost as accurate relies on the fact that two of the four spider vanes in the R200SS telescope are set exactly in line with the axis of the focusser draw tube. This means that when the telescope tube is rotated in its mounting rings so that the focusser draw tube lines up with the counterweight bar (as is usually the case) the diffraction spikes displayed around a bright star will always be aligned N, S, E and W. It is then simply a matter of rotating the camera until the diffraction spikes line up with the reticle's crosshairs.