Absolutely true. There is no substitute for a good if not excellent
polar alignment. With the increased size of imaging detectors, it
becomes more and more crucial to have a proper polar alignment for
long duration exposures. Field rotation results if polar alignment is
off and while it is negligible at or at close to 0 Dec, it becomes
pronounced and impossible to deal with in virtually any other manner
if one is imaging above/below +/-60 Dec and the closer one is imaging
to +/-90 Dec the worse it gets depending on the polar misalignment.
I have several useless large format images to prove the point after I
managed to trip over a leg and thought that I didn't move the mount.
Guiding is for correcting the inherent drive errors in the mount and
can be useful to help overcome atmospheric refraction somewhat in a
series of long exposures, not for correcting poor mount alignment.
Rick.
--- In ap-gto@..., "roy uyematsu" <roystarman@...> wrote:
I am very late to this discussion but from what I've read, I think
you maybe
making an assumption that is not true. That is Autoguiding can help to
overcome polar alignment issues and mount problems. To some extent
this is
true but the real reason for autoguiding is to correct errors in the RA
drive periodic error and others. If you are having to make regular
and large
declination corrections then you have either a polar alignment issue
or a
backlash issue. You should be working to minimize the number of
corrections
required, not trying to determine the fastest rate you can put them
in. As
you have stated each time the mount moves there is settling and other
issues. So it seems very reasonable that you want to minimize the
movements.
Try get to a regime of 5 second as a minimum and probably more like
10 to
15. If you use narrow band filters you will probably need 20 to 30
seconds
perhaps more to find a good guide star.
Roy Uyematsu
roystarman@...
_____
From: ap-gto@... [mailto:ap-gto@...] On
Behalf Of
Murray Hammick
Sent: Friday, March 28, 2008 12:25 PM
To: ap-gto@...
Subject: Re: [ap-gto] Re: Autoguider correction frequency
I use the Orion SSAG with an AT 66ED and AP900 using the on-camera
setting
and a refresh rate of .5 sec. Seems to work well - but will try it
at one
and five seconds this weekend.
With very low settings for aggressivenss and high averaging, the shorter
exposure times seemed more rational - but per the above I iwll try it on
much slower settings
Murray
Gedas <HYPERLINK "mailto:w8bya%40mchsi.com"w8bya@...> wrote:
Correct, it's the orion AG'er.
Gedas
HYPERLINK "http://gedas.cc"http://gedas.-cc
HYPERLINK "http://www.w8bya.com"http://www.w8bya.-com
----- Original Message -----
From: "hewholooks" <HYPERLINK
"mailto:hewholooks%40yahoo.com"hewholooks@...>
To: <HYPERLINK "mailto:ap-gto%40yahoogroups.com"ap-gto@...>
Sent: Friday, March 28, 2008 11:53 AM
Subject: [ap-gto] Re: Autoguider correction frequency
So you are using your "on camera" guider and not something like a DSI
or independant webcam to guide with.
Thanks,
Hunter
--- In HYPERLINK "mailto:ap-gto%40yahoogroups.com"ap-gto@...,
"Gedas" <w8bya@> wrote:
That's a good question Hunter. As far as I know I have not loaded
ASCOM
onto this newly populated pc yet so I did not even access the panel
you
mention. I just selected on-camera for mount type in PHD. I
should have
double checked the guide rate on the AP hand controller however.
The last
time I tried AG it was set to 1x and assumed it did not change,
that's a
poor assumption on my part, I should have looked.
Gedas
HYPERLINK "http://gedas.cc"http://gedas.-cc
HYPERLINK "http://www.w8bya.com"http://www.w8bya.-com
----- Original Message -----
From: "hewholooks" <hewholooks@>
To: <HYPERLINK "mailto:ap-gto%40yahoogroups.com"ap-gto@...>
Sent: Friday, March 28, 2008 11:04 AM
Subject: [ap-gto] Re: Autoguider correction frequency
Gedas,
What guiding rate did you set the AP ASCOM driver to (on the ASCOM
panel - NOT the PHD settings) when you used PHD - I believe it has
1x, 0.5x, and 0.25x as choices. I was wondering which to use
when I
give it a try. Also, while I'm asking, what RA aggressiveness did
you select.
Hunter
--- In HYPERLINK
"mailto:ap-gto%40yahoogroups.com"ap-gto@..., "Gedas" <w8bya@>
wrote:
Murray, I use a 900GTO and the Orion guider along with PHD. Last
week I
tried the guider for the first time and found that for my rough
polar
alignment and available stars, 2 second exposures provided me
with
perfect
round stars for my 15 minute test frame. I'm sure I could have
gone longer
between exposures but since it worked I didn't mess with the
settings after
that. One note, I did have to reduce the ms step size from (I
think the
default was 1000ms) to like 100ms. By default, the cal star
would
quickly
leave the cal box if left alone. Once I changed it to 100ms,
this
reduced
how far the mount would move and I had solid guiding.
Gedas
HYPERLINK "http://gedas.cc"http://gedas.-cc
HYPERLINK "http://www.w8bya.com"http://www.w8bya.-com
----- Original Message -----
From: "mphammick" <mphammick@>
To: <HYPERLINK
"mailto:ap-gto%40yahoogroups.com"ap-gto@...>
Sent: Thursday, March 27, 2008 4:18 PM
Subject: [ap-gto] Autoguider correction frequency
I have just bought the Orion Starshoot autoguider camera and
have
got
some very sharp images with a TAK scope on an AP900 mount.
Has anyone else tried this system and if yes, what frequency
setting
do they have for the corrections. I have a friend with a
Paramount ME
who says his guider corrects 10 times a second; this seems
rather
high
to me. Does anyone have strong views as to how often the guider
should
correct a reasonable AP900 ?
Murray
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