Quote:
Originally Posted by mynameiscd
Hi all,
And thats when the penny dropped! !!
My scope is not aligned with my my mount!!!
I have never checked if its spot on with the mount and taking it off all the time of course there will be variation but its the mount is what needs to be spot on and not the scope and thats why the drift alignment is always right.
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Hi Andy,
Specifically the optical axis of the optical tube assembly (OTA) needs
to be precisely at right angles to the mount's declination axis.
Since many OTA's on German Equatorial mounts are mounted via rings
or dovetail plates, if sufficient care is not taken then the OTA will not
be "square" with respect the mount.
An optical axis to declination axes non-perpendicularity will result
in the OTA pointing away from the pole when the mount is otherwise
oriented to be pointing at it. This is termed "collimation error".
The direction of the error will also reverse when the OTA undergoes
a median flip.
It is a phenomena that surveyors have known about and corrected for
when using theodolites for the past several hundred years. Traditionally
they would take both a "face left" and "face right" observation with
the instrument by doing the equivalent of a meridian flip where the
telescope would become inverted. With the two readings in hand, they
could correct for the collimation error of the instrument.