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John/Keith:
=20
I do the exact same thing--unlock the RA clutch and rotate the scope =
around the axis of the fork arms. Once the stars appear to spin in a =
circle aroundd tthe center of the FOV, you know the OTA is in alignment =
with the fork arms. Once that is donw, then I do the drift alignment, =
but only if I plan on doing astrophotography. If I am simply doing =
visual, I do the normal meade 2 star/automatic alignment.
=20
Bruce Johnson of this group has an excellent website that explains the =
concepts behind Drift alignment. It is how I learned to do it right. =
Check it out:
=20
http://members.aol.com/ccdastro/drift-align.htm
=20
Bill Drelling


--- Keith wrote:

> Hi John. Thanks for the feedback. I'm delighted to hear that
> I can use the SBIG STV eFinder scope for drift method polar
> alignment, even if it and the main scope are not center
> aligned with each other. There's one thing I didn't say
> about how I do my drift alignment, and maybe this is
> important? My east and west views along the celestial
> equator are blocked, and I can only see about +/- 15deg
> either side of due south. (my view nearer the zenith and to
> the north are much more open) So, I did my drift alignment
> and mount adjustments so that the star stayed in the same
> place (up/dwn & left/right) doing just the azimuth drift
> test.=20

Normally you only check for dec (up/down) drift when using the drift
method. If you adjust the az until there's no dec drift when aimed
near the meridian, then your az is OK, and you won't get rotation as
long as you image near the meridian. But if your wedge alt is off,
you'll still get rotation if you image in the northeast or northwest.

But if your wedge alt is off, the tracking rate when near the meridian
will also be a bit off. So you _could_ test for that by looking for RA
(left/right) drift during the drift test. In other words, use the dec
drift as usual to check the wedge az when aimed near the meridian, but
the RA drift indicates the alt is off. But drive error will also cause
RA drift, so I don't know how useful this method would be in practice.

Meade's basic polar alignment method is actually very good, except for
one obvious weak point, which is easily cured. It starts by relying on
the dec setting circle to get you to 900, but setting circles are prone
to slipping, and can't be read very accurately. But when at 900, the
tube should be parallel to the mount's RA aixs, so if you look through
the scope while rotating in RA (loosen the RA clutch and move it
manually), the image should rotate around the center of the FOV (stand
on the south side and swing the diagonal up between the forks so you
can view). If the image doesn't rotate around the center of the FOV,
tweak the dec until it does.

I've been using this method for years and it works so well that I no
longer bother with the drift method. Meade has since added this tip to
the polar alignment instructions for the GPS scopes.

-John



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<DIV>John/Keith:</DIV>
<DIV>&nbsp;</DIV>
<DIV>I do the exact same thing--unlock the RA clutch and rotate the =
scope around the axis of the fork arms.&nbsp; Once the stars appear to =
spin in a circle aroundd tthe center of the FOV, you know the OTA is in =
alignment with the fork arms.&nbsp; Once that is donw, then I do the =
drift alignment, but only if I plan on doing astrophotography.&nbsp; If =
I am simply doing visual, I do the normal meade 2 star/automatic =
alignment.</DIV>
<DIV>&nbsp;</DIV>
<DIV>Bruce Johnson of this group has an excellent website that explains =
the concepts behind Drift alignment.&nbsp; It is how I learned to do it =
right.&nbsp; Check it out:</DIV>
<DIV>&nbsp;</DIV>
<DIV><A =
href=3D"http://members.aol.com/ccdastro/drift-align.htm">http://members.a=
ol.com/ccdastro/drift-align.htm</A></DIV>
<DIV>&nbsp;</DIV>
<DIV>Bill Drelling</DIV>
wrote:</DIV>
<BLOCKQUOTE class=3Dreplbq style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #1010ff 2px solid">--- Keith =
feedback. I'm delighted to hear that<BR>&gt; I can use the SBIG STV =
eFinder scope for drift method polar<BR>&gt; alignment, even if it and =
the main scope are not center<BR>&gt; aligned with each other. There's =
one thing I didn't say<BR>&gt; about how I do my drift alignment, and =
maybe this is<BR>&gt; important? My east and west views along the =
celestial<BR>&gt; equator are blocked, and I can only see about +/- =
15deg<BR>&gt; either side of due south. (my view nearer the zenith and =
to<BR>&gt; the north are much more open) So, I did my drift =
alignment<BR>&gt; and mount adjustments so that the star stayed in the =
same<BR>&gt; place (up/dwn &amp; left/right) doing just the azimuth =
drift<BR>&gt; test. <BR><BR>Normally you only check for dec (up/down) =
drift when using the drift<BR>method. If you adjust the az until
there's no dec drift when aimed<BR>near the meridian, then your az is =
OK, and you won't get rotation as<BR>long as you image near the =
meridian. But if your wedge alt is off,<BR>you'll still get rotation if =
you image in the northeast or northwest.<BR><BR>But if your wedge alt is =
off, the tracking rate when near the meridian<BR>will also be a bit off. =
So you _could_ test for that by looking for RA<BR>(left/right) drift =
during the drift test. In other words, use the dec<BR>drift as usual to =
check the wedge az when aimed near the meridian, but<BR>the RA drift =
indicates the alt is off. But drive error will also cause<BR>RA drift, =
so I don't know how useful this method would be in =
practice.<BR><BR>Meade's basic polar alignment method is actually very =
good, except for<BR>one obvious weak point, which is easily cured. It =
starts by relying on<BR>the dec setting circle to get you to 900, but =
setting circles are prone<BR>to slipping, and can't be read very =
accurately. But when at 900,
the<BR>tube should be parallel to the mount's RA aixs, so if you look =
through<BR>the scope while rotating in RA (loosen the RA clutch and move =
it<BR>manually), the image should rotate around the center of the FOV =
(stand<BR>on the south side and swing the diagonal up between the forks =
so you<BR>can view). If the image doesn't rotate around the center of =
the FOV,<BR>tweak the dec until it does.<BR><BR>I've been using this =
method for years and it works so well that I no<BR>longer bother with =
the drift method. Meade has since added this tip to<BR>the polar =
alignment instructions for the GPS =
scopes.<BR><BR>-John<BR><BR><BR><BR>__________________________________ =
<BR>Do you Yahoo!? <BR>Make Yahoo! your home page =
<BR>http://www.yahoo.com/r/hs<BR>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
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=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D<BR>For help and information on =
the Acceptable Use Policy, =
visit<BR>http://www.mapug-astronomy.net/pages/Subcrb_AcceptUse.html<BR><B=
R>MAPUG is hosted by Software-y-Ddraig (Dragon Software)
=
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