#### Re: Orthogonality question

jimmyjujames

If OE is short for orthogonality error.

An Orthogonality error (OE) is only east-west when pointing at zenith or along meridian.
OE is always in line with the counter-weight shaft.
When pointing at NCP with counter-weight shaft pointing down, OE is north-south.

What is an orthogonality error (OE)?

With the counter-weights down and scope pointing at NCP.
An orthogonality error will cause the scope's viewing point to be above or below NCP.

To the left or right of NCP is not an error.
You can move Dec to remove any left or right offset.

Rotating RA from east side to west side will move the scope's
viewing point around NCP tracing out half of a circle around NCP.
Scope will hit the pier before the other half of circle completes.

Diameter of the circle is 2 times (2x) your orthogonality error.

If you move the counter-weight shaft to west side and horizontal/level with ground, the scope's
viewing point will be either east or west of NCP by (1x) your orthogonality error.

If you move the counter-weight shaft to east side and horizontal/level with ground,
you will miss NCP by 1x on the other side of NCP.

1x on one side of NCP, meridian flip and 1x off on other side = 2x orthogonality error when
flipping from east to west side.

If you move scope from NCP to zenith to Dec=0 to SCP, your scope's viewing point will be east or
west of meridian by your 1x orthogonality error everywhere along that path.

You will have to shim the front or rear ring to bring your viewing point back to NCP.