[APML]: Re: polar alignment

[byen@ix.netcom.com]

Mike Regish wrote:

>        I use the polar alignment reticle in the finder scope to get me
>close. That's been good enough for 10 minute unguided wide angle shots, so
>it gets me pretty close.

When I had a 8" fork mounted scope, I never bothered with this (although you 
should be right about getting close).  The below method saves from "messing" with 
the altitude adjustment (from your last outing).

  Make sure you have enough leeway on either side of azimuth adjustment ("center" 
it).   Stand off of tripod looking north, and swing your arms vertically (palms 
vertical) "slicing through the mount".  You want to bisect Polaris, so turn the 
tripod/wedge until this happens.  Then level the tripod, always (reason for this 
later).  I use the "binary chop" method for "drifting on meridian star".  I will 
usually see some DEC drift fairly quickly (within 15 sec), and can get a "feel" of 
how far off it is.  JUST nudge the scope towards the north (towards Polaris) to 
see what direction the star is driftng (no need to worry about diagonals, 
left-right reversal etc).  Then make azimuth adjustment so the star "moves" a 
multiple of eyepiece FOV diameters (1/2, 1, 2 - you have to make a good guess 
here), to get DEC drift in the OPPOSITE direction.  By remembering how many FOV 
diameters you went, you know you have to be somewhere in between.  So HALVE this, 
and make an azimuth adjustment in other direction.  Repeat this, you should 
converge fairly quickly.  Actually, I have such a good "feel" from practice, I can 
go "right to it" (without having to get DEC drift in opposite direction).  Since 
you leveled tripod, your altitude setting from previous outing should be pretty 
close.  So, when you "drift on the eastern horizon star" - only minimal altitude 
adjustments are required.


 <"guessing" azimuth direction, when drift aligning meridian star.>
 
********** begin of exchange
   
Steve Bell wrote:

> > >If there is DEC
> > >drift, move the mount in azimuth a tweek - just choose either east or west
> > >at first.
> > >Watch again. If it drifts worse, then tweek back in the opposite
> > >direction. If it
> > >drifts less, then you're tweeking in the correct direction. Tweek until
> > >there is
> > >little or no DEC drift over a few mins.

Chuck Vaughn wrote:

> > Certainly that will work, but if you're _far_ off and you see drift in only
> > a few
> > seconds (which is common) you'll have to precisely time and measure the
> > drift to see
> > which direction you went after you make an adjustment, especially if the
> > adjustment
> > is small compared to amount you need to move.
> >
>
Steve Bell wrote:

> Yes, I was assumming that one has their polar axis reasonably lined up on the pole to
> begin with. I'm not sure why you'd have to precisely time anything (other than has it
> drifted too much (> 5-10 arc sec) in the last 5 mins - and you don't have to be too
> precise here). Of course, you do have to note what direction in the eyepiece the star
> is drifting in, and by trial and error you can rapidly find out what tweek direction
> corresponds to nulling out what drift direction.

Dan Baldwin wrote:

>Well memorizing how to do it or consulting some instructions is helpful--I
>like Chuck, have a mental block regarding this, especially with the
>way that mirrors and diagonals invert things-- When I first started
>drift aligning, I tried it w/o consulting anything-- I started with
>a star on the meridian and near the equator, adjusted the elevation,
>went to the east , adjusted the azimuth--well after about an hour,
>I figured I was doing this wrong !!! After consulting my little
>"sheet" , I figured it out--Now it makes perfect sense--the thing
>I can never remember is the direction that right hand turns of
>the az/el adjustments result in :-). Knowing that you are
>doing it right the first time will certainly make it quicker.

****** end of exchange


There should be NO guessing of what azimuth direction to make (see below).  Also, 
I always level my tripod.

All you have to do is nudge telescope north (towards Polaris), to find what 
direction the star is drifting.  Then you should remember (or have pasted on your 
mount like K. Zussman does), what azimuth direction to go.  Me, I just remember SE 
(drift South, move East) and NW (drift North, move West).  Note that I imagine a 
plane "slicing" through the mount towards the southern horizon (which I'm looking 
towards, during all of this).  It's easy to figure out how to accomplish this, 
with the 2 knobs that "push" from either side.  The Losmandy G11 mount uses a 
threaded screw, which doesn't make this intuitively obvious.  So, I just paste 
some tape, denoting what knob direction will effect an East or West azimuth 
adjustment.

 Actually, I have found the G11 polar bore scope to be pretty accurate.  However, 
I have to do the alignment AFTER loading all my gear (requiring ~36 lbs of 
counterweights).  Because, the weight will move the equatorial head in altitude 
(you can hear it screech under the strain).  Anyone else have this?