wvreeven wrote: The polar alignment error is an angle calculated irrespective of the used coordinate system. The correction vectors are projections in the local azimuth and altitude system but could be any other coordinate system. As long as you make sure that the selected star ends up at the other side of those projected vectors, you’re good. Whether or not the mount is level is irrelevant.
This is not correct. The axes used for the correction matter. If it didn't and any way of moving the scope to put the target star in the calculaed position was OK you could use Ra and Dec movements to do this. This would obviously have no effect on the polar alignment.
That makes no sense Chris. In effect you are saying that if the mount is out of polar alignment, e.g. because a previously polar aligned mount has been set up with a tripod leg not extended properly, then the calculated correction is going to be wrong simply because the mount alt and az do not correspond to terrestrial alt and az. If that were the case the tool would never work at all. Of course it is essential that only the alt and az controls are used and the scope is not moved from its position when the star is selected
But once the polar misalignment is known in alt/az it is fairly trivial to calculate to calculate what movement is needed for a given star in HA/Dec and display where the guide star should be moved. As long as it is moved using the alt and az controls only then polar alignment should be achieved.
It sounds like the same erroneous argument as to why a mount should be level to polar align it.
I'll try yet again.
Yes, you can rotate the mount about any set of coordinates to correct for a polar align error. But the correction indication determined by using a reference star will depend on the position of the star determined in the coordinate system of the correction axes.
There are a number of positions which need to be avoided, for example for the normal Alt Az corrections a star at the zenith will be a poor choice for the azimuth correction because adjusting this axis will not move a star at the zenith. Similarly looking East or West won't work for the elevation correction. The optimum positions are fairly close to the meridian and away from the zenith. Avoid a band running overhead from East to West.
Your tripod leg length error will have the effect of rotating the mount about an axis defined by the other legs and in theory the required corrections could be determined in that coordinate system. You could then get a correction that could be corrected by adjusting tripod legs. That's going to be tricky to determine. Simpler to determine the error in the AltAz system and correct in that system.
Not having the mount level will make a difference but as I said previously the effect will be small for small errors, about one arc minute per degree of error or level.