Quick star drift alignment (was: Re: Some questions from a Losmandy user)
Yesterday night was the first time that I tried the GTO Quick star
drift method (meridian delay).
Procyon for alt adjustments (E of meridian)
Regulus and Dubhe for azimuth adjustments.
Not convincing so far, but this is my very first try and the clouds
did roll in very early, unfortunately. I need to figure out if I
overlooked something, hence the present post.
Alt adjustment was fairly simple; I was just surprised that I had to
specify a meridian delay of more than 1 hour (1E) although the
difference btw RA and LST was under 1 hour; anyway, I ended up
switching between 6E and 0W to be sure.
The simple thing is that a N-S keypad move and a change in Alt do
result in (nearly) parallel directions of move.
So, a good start.
Not so with my azimut adjustment, of course.
OK, I understand that the alt axis must be left untouched, same for N-
S keypad buttons.
The manual says the azimuth adjuster should be used "to correct half
of the error and the E-W buttons to finish centering".
The E-W buttons trigger a move in directions which are not parallel
to the one from the alt axis (looks normal), so what is actually
to be done ? Use the alt adjuster to move halfway to the reticule
axis then use the E-W to bring the star at the middle of the reticled
eyepiece (if ever possible ?)
Thanks for clarification.
--- In ap-gto@..., chris1011@... wrote:
methodorthogonal; I have yet to verify (and I thought the 2 stars
scope to awould minimize this problem if any).You can check orthogonality in about 30 seconds. Simply point the
star overhead (put star on crosshair at low to medium power) on oneside of
the mount, then do a meridian delay, enter the same star again anddo a goto.
The scope will now swing around to the other side of the mount andpick up the
same star. Any E-W difference is twice your scope's orthogonalerror. Any N-S
difference is twice your altitude error.instantly
know your orthogonal error, but you also can fix very quickly yourpolar
alignment error in the altitude axis. How? Simple, my dear. Justmove the star in the
N-S direction 1/2 way with the altitude adjuster. Go back and forthbetween
east and west a few iterations until the star is placed on thecrosshair each
time, and you are done. Takes only a minute for each GoTo. No moreadjustment of
the altitude axis is needed - you have adjusted this axis without apolar
scope and without knowing exactly where north is, and all withoutany kind of
complicated software (by the way I doubt that one can get within 5arc sec of the
pole with the Losmandy software, or at least I am very skeptical -besides
one needs to offset from the pole in order to eliminate driftanyway).
up the azimuth, and that is even simpler. In fact, I could probablydo it
blindfolded, well not really, but almost. Since altitude is nowfixed, you just
need to adjust the azimuth until you get no drift in Dec. Or youcan use two
stars, one in the north, and one in the south. Slew between themand adjust the
azimuth until they fall on the crosshairs (don't touch thealtitude!!).
before the sun has set and do precision drift alignment beforetwilight is
done. The whole process takes 15 - 20 minutes at most. I don't usethe polar
scope much, except for when I'm lazy and have people around who areasking
questions and I can't concentrate on alignment the other way.equatorial
mount, you really can do polar alignment in an intelligent way andquickly
too. Otherwise you will be a slave to your computer.NCID=aolcmp00300000002548)