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Date: 16 Sep 2007 03:34:43
From: canopus56
Subject: Drift polar align - east test?
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I am confused about the east horizon test for polar drift alignment.
Most instructions appear to say that one should find a star due east
on the celestial equator. But the celestial equator crosses the
eastern horizon at a zero degrees altitude. Do you in fact have to
pick a star on the celestial equator somewhat east south east in order
to have a drift alignment star with sufficient altitude? - Canopus56
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Date: 16 Sep 2007 14:52:19
From: canopus56
Subject: Re: Drift polar align - east test?
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On Sep 16, 8:04 am, "Steve Paul" <smarshallp...@gmail.com > wrote:
<snip >
Thanks to all. The answer to my narrow question regarding the
altitude adjustment is that it is not "due" east but any star "in the
eastern sky" near the celestial equator. Practically, this means
somewhere east-southeast, where the celestial equator has enough
altitude to conveniently acquire a target, but still as close to the
horizon as possible. Same principle applies to using a western sky
star. - Thanks, Canopus56
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Date: 17 Sep 2007 10:40:19
From: AM
Subject: Re: Drift polar align - east test?
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canopus56 wrote:
> On Sep 16, 8:04 am, "Steve Paul" <smarshallp...@gmail.com> wrote:
> <snip>
>
> Thanks to all. The answer to my narrow question regarding the
> altitude adjustment is that it is not "due" east but any star "in the
> eastern sky" near the celestial equator. Practically, this means
> somewhere east-southeast, where the celestial equator has enough
> altitude to conveniently acquire a target, but still as close to the
> horizon as possible. Same principle applies to using a western sky
> star. - Thanks, Canopus56
>
Once you have done this a lot, it will become
instinctive. You will find that it takes less
time to do a nice drift alignment than all the
talking ya do with your observing buddies when
ya first show up at an observing site.
BTW, the polar scope option is viable, and used
properly will get you a pretty good alignment.
--
AM
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Date: 17 Sep 2007 21:45:02
From: Steve Paul
Subject: Re: Drift polar align - east test?
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"AM" wrote :
> BTW, the polar scope option is viable, and used
> properly will get you a pretty good alignment.
>
I always liked the Vixen PS that came with my Celestron GP-C102-ED mount.
Once I figured it out, it was really quite amazing how accurate it was.
When I first started imaging with a DSLR and an F4 800mm focal length, I
could get away without a drift alignment for the unguided 30 second
subframes I was grabbing of M42 in winter and M8 in summer.
The trick was to follow the instructions in the book, not only for the polar
alignment, but the bit about aiming the PS at an object in the distance and
rotating the RA axis to get it properly aligned to the bore in the first
place.
-Steve P.
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Date: 18 Sep 2007 11:02:10
From: Per Erik Jorde
Subject: Re: Drift polar align - east test?
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"Steve Paul" <smarshallpaul@gmail.com > writes:
> "AM" wrote :
>
>> BTW, the polar scope option is viable, and used
>> properly will get you a pretty good alignment.
>>
>
> I always liked the Vixen PS that came with my Celestron GP-C102-ED
> mount. Once I figured it out, it was really quite amazing how accurate
> it was.
Agreed. I do mostly CCD imaging now and always rely on the polar scope
on my vixen GP-DX. Drift aligning would take too much time every time
I set up. With PEC enabled, I regularly shoot 4 minute exposures with
my F/1800 mm Mak. During a typical 1.5 hour session there will be
accumulated maybe 30 arcsecond drift in Dec.
pej
--
Per Erik Jorde
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Date: 16 Sep 2007 13:51:10
From: William Hamblen
Subject: Re: Drift polar align - east test?
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On Sun, 16 Sep 2007 03:34:43 -0700, canopus56 <canopus56@yahoo.com >
wrote:
>I am confused about the east horizon test for polar drift alignment.
>Most instructions appear to say that one should find a star due east
>on the celestial equator. But the celestial equator crosses the
>eastern horizon at a zero degrees altitude. Do you in fact have to
>pick a star on the celestial equator somewhat east south east in order
>to have a drift alignment star with sufficient altitude? - Canopus56
The reason to use a star near the equator is that it drifts faster.
The reason to pick an eastern star is that it won't set before you
finish if it happens to take longer than you expect to drift align.
"Close enough" is close enough.
Bud
--
The night is just the shadow of the Earth.
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Date: 16 Sep 2007 07:38:11
From: William R. Mattil
Subject: Re: Drift polar align - east test?
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canopus56 wrote:
> I am confused about the east horizon test for polar drift alignment.
> Most instructions appear to say that one should find a star due east
> on the celestial equator. But the celestial equator crosses the
> eastern horizon at a zero degrees altitude. Do you in fact have to
> pick a star on the celestial equator somewhat east south east in order
> to have a drift alignment star with sufficient altitude? - Canopus56
>
I usually use an Eastern star about 20 to 30 degrees up from the horizon.
Bill
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Date: 16 Sep 2007 10:16:00
From: AM
Subject: Re: Drift polar align - east test?
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William R. Mattil wrote:
> canopus56 wrote:
>> I am confused about the east horizon test for polar drift alignment.
>> Most instructions appear to say that one should find a star due east
>> on the celestial equator. But the celestial equator crosses the
>> eastern horizon at a zero degrees altitude. Do you in fact have to
>> pick a star on the celestial equator somewhat east south east in order
>> to have a drift alignment star with sufficient altitude? - Canopus56
>>
>
>
>
> I usually use an Eastern star about 20 to 30 degrees up from the horizon.
>
>
> Bill
Same here.
Here is a nice webpage on polar aligning for
canopus56 to read;
http://www.darkskyimages.com/gpolar.html
To get close upon initial setup, I use a
compass, to set azimuth, and a protractor
to set elevation of the tube. It cut's
my drift alignment time in half.
YMMV
--
AM
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Date: 16 Sep 2007 10:04:40
From: Steve Paul
Subject: Re: Drift polar align - east test?
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"William R. Mattil" <wrmattil@ix.netcom.com > wrote in message
news:rs9Hi.3268$Sd4.1834@nlpi061.nbdc.sbc.com...
> canopus56 wrote:
>> I am confused about the east horizon test for polar drift alignment.
>> Most instructions appear to say that one should find a star due east
>> on the celestial equator. But the celestial equator crosses the
>> eastern horizon at a zero degrees altitude. Do you in fact have to
>> pick a star on the celestial equator somewhat east south east in order
>> to have a drift alignment star with sufficient altitude? - Canopus56
>>
>
> I usually use an Eastern star about 20 to 30 degrees up from the horizon.
>
Think of it this way...
I drift align/image west because I don't have a good eastern horizon....
I use a star that's far enough above the tree-tops to still be visible
before I'm done drifting. :-)
-Steve P
(When I was imaging)
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