Hi!
You are a star, Ray! For the first time, I feel like I understand it better! (Sorry for the "straight into the ground" - I only got half of my thinking there. Of course not straight, but somewhat down into the ground....)
Now, I have made a bunch of screenshots, here in a shared Dropbox-folder:
To be viewed in this sequence:
Start.png
DEC_65.png
DEC_102.png
DEC_132.png
SV.png
NV.png
What I did was to place the mount in zero mechanical Dec/HA (roughly). That is Start.png (I apologize for everything being in Swedish). You see the mount on the star map, and the side of pier in the window to the lower right, where "?st" means East. THe coordinates are given in the window top right - "Dek" is declination, "ELEV" is altitude.
Now I move the mount in Dec only, up past the pole. DEC_65.png is in the way up. Still side-of-pier is East (?st) as it should be. THen I cross the pole to DEC_102.png (I had to cross the meridian too, to avoid a flip). Still it is East (?st) - but now it should be West, right? But it is still East! Further down on the north side to DEC_132.png, and still East.
The way I interpret it, this is not consistent with how side of pier is defined in that ASCOM document you linked to, Ray. Or do I misinterpret?
The last two is where it DOES shift side of pier. THat is pointing in what I call south west (SV.png), then slewing to north west (NV.png). THis is a slew in RA, mainly. And not much shift in Dec, at least not going beyond ¡À 90 degrees. But here it shifts.
Is this correctly understood now?
Best,
Magnus
Den 2020-04-21 kl. 16:27, skrev Ray Gralak:
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Magnus,
If I move the scope to - 90 degrees Dec, it will point straight into the ground, wouldn't it? TO the south celestial
pole.... And I could to that if I lived on the equator.... Dec = -90 is not straight at the ground unless you are at the north pole. :-)
For example, if your latitude is 40 degrees then the north celestial pole is 40 degrees above the horizon. The horizon at due south is -50 degrees latitude, and south celestial pole 40 degrees below the southern point of the horizon (not 90 degrees south of it).
-Ray Gralak
Author of APCC (Astro-Physics Command Center):
Author of PEMPro V3:
Author of Astro-Physics V2 ASCOM Driver:
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Magnus Larsson
Sent: Tuesday, April 21, 2020 7:19 AM
To: [email protected]
Subject: Re: [Losmandy_users_io] Side-of-pier issue
Hi!
OK, I see what you mean by declination axis. Just to understand, though:
"Mechanical zero HA/Dec will be one of the two ways of pointing at the intersection of the celestial equator and
the local meridian. In order to support Dome slaving, where it is important to know which side of the pier the mount
is actually on, ASCOM has adopted the convention that the Normal pointing state will be the state where a
German Equatorial mount is on the East side of the pier, looking West, with the counterweights below the optical
assembly and that pierEast <
standards.org/Help/Platform/html/T_ASCOM_DeviceInterface_PierSide.htm> will represent this pointing state."
If I place my mount in this position, it will point straight to the south, right? Where the celestial equator intersects
the local meridian - south, in my case ca 25 degrees altitude (I'm at 55 degrees North). So that is zero mechanical
Dec and HA?
If so, how should I understand this?
Normal (pierEast <> )
Where the mechanical Dec is in the range -90 deg to +90 deg
If I move the scope to - 90 degrees Dec, it will point straight into the ground, wouldn't it? TO the south celestial
pole.... And I could to that if I lived on the equator....
So if I in this position, without moving the RA/HA-axis, move the dec to somewhere north - that would be beyond
+90 degrees - then I should have a shift of side-of-pier?
Magnus
Den 2020-04-21 kl. 15:51, skrev Ray Gralak:
Magnus,
Take a look at this link for a detailed explanation:
-Ray Gralak
Author of APCC (Astro-Physics Command Center):
Author of PEMPro V3:
Author of Astro-Physics V2 ASCOM Driver:
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Magnus
Larsson
Sent: Tuesday, April 21, 2020 6:29 AM
To: [email protected]
Subject: Re: [Losmandy_users_io] Side-of-pier issue
Hi!
Thanks for your reply!
However, I am not sure I understand - which is not surprising because I
find this to be a difficult issue to describe and understand. I think
the hour angle description was the clearest so far, for me...But, I
don't know what Gemini uses to detect a shift of side-of-pier.
I don't follow what you mean by declination and RA-axis position. My
side-of-pier shifts when I slew in RA, not in DEC (don't know how to do
that). Of course my DEC axis moves, since it rotates around the RA axis.
But it is the slew in RA that causes a shift in side-of-pier, as the
counterweight bar (to describe it physically) moves across the meridian.
I guess that is what you mean by "note that when doing that the actual
pier side change occurs when the declination axis passes the celestial
pole to the other side"?
Either way - whichever axis moves and whatever causes the shift in
side-of-pier - maybe I describe it in totally wrong words. But: my PHD2
reacts to a shift in side-of-pier when I slew from some variables to
certain others - without any meridian flip nor a need for any - because
both stars are on either west or east side of the mount. This is my
problem, and it seriously messes up my variable sequences.
Maybe I describe it in odd ways - but the unusable images are very
real.... so how can we describe it in a reasonable way, and maybe find a
way to handle it?
Best,
Magnus
Den 2020-04-21 kl. 14:17, skrev Ray Gralak:
Hi Magnus,
I'm not sure if this has been said before, but "pier side" is determined by declination axis
position alone. It is not
affected by the right ascension axis position, so slewing the mount to "N", "NW", "S", etc. doesn't
provide enough
information to determine side of pier.
Specifically, pier side changes at the celestial pole when the Dec axis passes through 90
degrees (or -90
degrees).
A change in pier side often is associated with the mount "flipping" to the other side but note
that when doing
that the actual pier side change occurs when the declination axis passes the celestial pole to the
other side.
-Ray Gralak
Author of PEMPro V3:
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Magnus Larsson
Sent: Tuesday, April 21, 2020 2:57 AM
To: [email protected]
Subject: Re: [Losmandy_users_io] Side-of-pier issue
Hi!
How's it going with this? Makes any more sense? On the indi-forum, it is spoken about
in terms of hour angle,
maybe better way. My test shows that between -3 and -9 hours, the side-of-pier shifts
(approximately at -6) and
the
same happens between 3 and 9 hours.
So these are shifts of side-of-pier in situations where there should not be a meridian
flip (and none is initiated).
See the indi-forum thread here:
problem-bug.html
Best,
Magnus
Den 2020-04-19 kl. 18:28, skrev Brian Valente:
I generally understand your somewhat unusual case
What i don't understand is this: when I want to go from NE to SE, that is a slew
in DEC for me. you're
saying slew in RA, and I don't see how i would get to SE just by moving RA?
On Sun, Apr 19, 2020 at 9:19 AM Magnus Larsson <magnus@...>
<mailto:magnus@...> wrote:
Hi!
No, it is a slew in RA - I'm doing it with the same declination, just slewing
in RA, to test. And right, no
crossing the meridian. But physically, crossing the 90 degree azimuth line, the
counterweight bar crosses to
the
other side of the mount - hence shift of side-of-pier, in a very literal sense.
Yes, it impacts my guiding since when the mount reports shift of side-of-
pier, PHD2 swaps direction
of RA guiding. But since no direction of the guidecam or otherwise in the mount has
happended, this means
that
RA now escalates errors, rather than works against them - hence escalating run away
scope.
In essence, PHD2 interprets shift of side-of-pier as a meridian flip. But
this is not the only case when
it occurs nor when the G2 reports it.
It took me quite a while to see this... And I guess this is not what would be
problematic in regular AP,
when you find a target, maybe calibrate, and then track for hours. Then there is a
meridian flip, RA shifts, and
back to tracking. It happens here because I slew from target to target, imaging 20-25
different targets with just
one
or two subs of each, but I need guiding because I do some 5 mins exposures and I get
too much drift if no
guiding.
I have my complex sequence set up so it goes from lower altitude to higher, picking
stars before they are too
low,
basically, and then waiting for some to rise some more (manually sorted). It means that
it will start out on the
west
side, going in sort of zig-zag motion from RR Tau to GM Cam, to YY Aur, to U Gem and
so on.
Do you see it now? Or what can I send or describe that makes it more
clear?
Best,
Magnus
Den 2020-04-19 kl. 17:48, skrev Brian Valente:
Hi Magnus
No, it doesn't really make sense to me. if i go from NE to SE, this is
just a DEC move, i'm not
crossing the meridian. So why would it report side of pier change? confused abou tthis
i can slew back and forth, but it sounds like your issue is how is
guiding impacted, correct?
So i would assume you need some guiding to take place in this
situation to see how it
impacts.
--
Brian
Brian Valente
portfolio brianvalentephotography.com <>
<>
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