Quote:
Originally Posted by frolinmod
I'll amend my statement about which is better. For instance, he following website says that it's better to align on the refracted pole at mid to high latitudes and better to align on the true pole at low latitudes
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Hi Ernie,
Unfortunately there is no magical point in the sky to which one can align the polar
axis of an equatorial scope and then achieve zero field rotation for all possible observing
positions in the sky.
At best, there is a different optimal point at which to align the polar axis for each
possible declination and hour angle the scope can be pointed at and for each possible
value of the local temperature, local air pressure and wavelength of light at
which one is observing. The latitude and elevation of the observatory are also
factors.
The details are complex.
However ...
The version of TPOINT Paul has is fine and has been used to successfully align the
world's largest and most expensive telescopes for over 30 years. A table appears
on page 29 of the user manual that has estimates for the difference between the
true and refracted pole for various latitudes and different observatory altitudes.
The values in the table are in arc seconds and one should, in the southern
hemisphere, simply add the appropriate value to the value for ME. This then
gives the position of the refracted pole. In any case, the refracted pole is always
lifted above the true pole.
As a compromise, at Paul's mid latitude location he should be aiming for the
refracted pole especially for observations within a few hours either side of the
meridian. At your equatorial station, go for the true pole.
Best Regards
Gary Kopff
Mt Kuring-Gai