NOVA 120 Pointing model user manual
21
As said previously, the telescope is aiming to the east side of the sky, because telescope tube’s is west from pier:
The idea is to have the telescope to scan this area with many fields, perform plate solving and create a list that contains
the actual telescope position and theoretical (or expected) position. To obtain a good pointing model, this scan must
have regularly sampled fields across the sky, and at least 20 fields (40 is better).
In the next sample, the fields are selected by PRISM so that meridian angle gap between fields will be set to 1h, the DEC
gap to 15°. All fields shall be at least 20° elevation above horizon. Since in this sample, southern hemisphere location
mount is used, the min DEC is set to -80° and max DEC to +45°. If northern hemisphere, say in the USA, theses figures
would be from DEC=-20° to +80°.
Meridian angle (or hour angle) can be from -12H to +12H, and since the “
East side of the Sky
” checkbox is checked, the
software will only select fields that are in this location and nowhere else, so that meridian flip of the mount will not
occur during this step.
Then click “
Create field list
”, the software will then build a list of field to be scanned.
In this case, 50 fields have been selected, not randomly but using a regular pattern of 15° in DEC direction and 1h in RA
direction.
Then select 10s of exposure, full frame, using 2x2 binning (here this is a 4096x4096 CCD used).
Check also “
If plate solving fails, tries ….
” This will allow the software to perform plate solving into neighborhood
locations in case it would fail in the center field. This can happen when the mount is really not well polar aligned or
optical axis and DEC axis errors exceeds more than 30’ (indeed has poor pointing performance).
