Celestron CG-5⁴, CGEM², C6-N, C6, C8, Nexstar 8SE, 6SE, ONYX 80 EDF, Orion ST 80 A Vixen R130SF w/Porta II mount William Optics ZS110 ED APO, FLT 132 Triplet APO, SV70 ED SV115T20 Wicháhpih'a
Quote:The program will choose the stars for you. If you do not like the stars that are choosen press undo/back and scroll until you find one you like. If you still don't see a star you like press the up/down button and scroll through a complete list of stars available.Stan
Uncle Rod Uncle Rod's Astroblog: http://uncle-rods.blogspot.com/
Quote:As an example, a few days ago I set up and did an align using Ralalhague and Albeiro with Deneb as a single calibration star. This gave a polar align error of 2' 45" in Azm and -47' 01" in Alt.I did an ASPA using Altair as the align star.I cycled power and did the same 2+1 align using the same stars.The polar align error was reported as 2' 41" in Azimuth and 1' 20" in Altitude.
Quote:Switches should not make a difference because you start at the align position and while this may not be as accurate as switches once you have two stars the mount has enough information to calculate the Ra and Dec offsets and the start position doesn't matter.
The two alignment stars do not tell you the dec. offset - it comes from the calibration - and the calibration needs to be good.
The RA switch offset is not critical and it is set by the alignment stars, but the dec. offset is different.
Multiple calibration stars help clarify the dec offset value - which presumably is different every time you manually align to the index mark. Changes in this value are another reason it is desirable to avoid powering off the mount and losing that value.
None of what I'm saying should detract from the accuracy of ASPA when it is done with 2+3 or 2+4 - which I expect to be within a few arc-minutes and adequate for long exposure guided imaging (as I do with my cge and cge-pro). But the accuracy is reduced a lot if you just use 2+1.