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:
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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:
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@...> 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 <>
