The model is needed in order to find out how the entire system deviates from a perfect system (perfectly rigid, with mount axes perfectly perpendicular, no slack, no atmospheric refraction and so on). The number of points needed is fundamentally driven by two factors:
- how imperfect the setup is in various azimuths and at various altitudes. The less rigid or less consistent the setup is, the more points are needed to characterize its behaviour.
- where you image in the sky. If you only plan to image one object in a given night, you don't need model points far from the trajectory of that object in the sky, so you can use fewer.
- the focal length. A higher FL will make deviations from pinpoint stars more visible.
- the exposure time. Longer times will allow deviations from pinpoint stars to become more visible.
The above factors do not depend on the accuracy of the polar alignment. Below is a quote from Filippo Riccio, one of the 10Micron software developers (he posted it on the 10Micron user forum) that clarifies things further:
"Effects of polar misalignment
Even if your mount is wildly away from a correct polar alignment, when you make a model the correction of the polar misalignment will be performed exactly.
This means that the pointing error and the tracking error will be the same - if you make a model with the same number of stars and the same accuracy - whether the mount is aligned with the celestial pole or not (note that the mount will prevent making a model if the error is too large, but this is only for sanity of the results).
This, of course, happens only if the dual axis tracking is selected. When dual axis tracking is deactivated, the mount will track like a normal equatorial mount, by moving the right ascension axis at a constant sidereal speed. The only important thing that will change is the field rotation"
How long does the modelling step take for a reasonable model? I would imagine that a longer FL scope will require more modelling points?
If I have a very good polar alignment, will that reduce the number of modelling points needed?
Edited by RazvanUnderStars, 11 February 2021 - 11:11 AM.