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08 Apr 2018
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TOPIC: Question on Polar Alignment Assistant

Question on Polar Alignment Assistant 3 weeks 3 days ago #26305

Hello all,

I see that there were some small changes to the polar alignment assistant
in KStars/Ekos version 2.9.6, particularly in regard to a rotation correction
for users in the southern hemisphere.

I have a quick question. I am in the *northern* hemisphere, but the scope
that I use for polar alignment uses a mirror diagonal, so that the "horizontal"
view is mirror-reversed. Will the polar alignment assistant work correctly
in this situation?

Thanks!

Greg

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Question on Polar Alignment Assistant 3 weeks 2 days ago #26312

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I use the main telescope with DSLR attached for polar alignment and I found that it doesn't matter what the orientation of the camera is. This is with 2.9.5 though and haven't been able to try 2.9.6 yet.

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Modded Canon EOS 700D with a WO ZS 71 ED on a SW HEQ5-Pro

Question on Polar Alignment Assistant 3 weeks 1 day ago #26348

Thanks for the reply wvreeven. I can understand how change of orientation would not
be significant, but it seems to me that mirror reversal may be, although I don't know
with certainty.

I conducted an experiment where I did a polar alignment in a west-rotating direction,
then attempted an alignment in an east-rotating direction (all of this, of course, with
a mirror-reversed view). They produced different results, i.e., the polar alignment
did not converge.

Greg

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Question on Polar Alignment Assistant 3 weeks 12 hours ago #26373

Hello again all,

Well, since I don't seem to have a definitive reply from the developers,
I will go ahead and conduct the experiment tonight (weather allowing),
by removing the diagonal and trying the alignment sequence.

I will post the result back here.

Gregory

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Question on Polar Alignment Assistant 2 weeks 6 days ago #26397

Hello again all,

Since the weather cooperated, I conducted the aforementioned experiment
last night.

It is only two trials, but my (otherwise uninformed) conclusion was that I
was indeed correct. Supplying a (horizontally) mirror-reversed image did
not work. When I removed the diagonal, and replaced it with simple
straight-through spacers, the Polar Alignment Assistant seemed to
work as advertised, and multiple passes converged.

This is not a "bug" exactly, but perhaps a request for a new feature.
My questions for the developers are: is it possible to ask for the "southern
hemisphere" style rotation even if one is in the northern hemisphere?
Would that solve my problem when using a diagonal? If so, where
would I ask for such a feature? If not, is there something else I can
do to make this work? Or am I wrong altogether? (doesn't appear
so from the experiment).

Thanks,

Greg

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Question on Polar Alignment Assistant 2 weeks 6 days ago #26401

Hello again,

As an afterthought -- does some expert out there know if there
is a way to request the download to mirror-reverse the image,
*before* it gets to the plate solve/alignment stage? That would
solve the issue neatly.

Greg

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Question on Polar Alignment Assistant 2 weeks 6 days ago #26402

Image rotation shouldn't matter, but a mirrored image certainly would have issues solving.I suggest not using the diagonal or getting a different guidescope.

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Question on Polar Alignment Assistant 2 weeks 6 days ago #26403

Hello lhoujin,

Thanks for the response. astrometry.net has no problem solving a
mirror-reversed image, so that is not the difficulty. The difficulty
(I imagine) rather is that the rotation used for polar alignment
adjustment is not correct, as it would not be for the southern
hemisphere, unless some modification were made (which is
apparently what was done in this last release).

Orientation is not a problem. Plate solving is not a problem.

I may have to examine what was done for southern hemisphere
accommodation, but I would like the opinion of a developer,
so that I am not chasing this problem the wrong way.

BTW, I am not using a guide scope, but rather I am using an
ONAG (on-axis guider), and aligning right through the main
(albeit small :-)) OTA. The ONAG is essentially a beam-splitting
diagonal.

Greg

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Question on Polar Alignment Assistant 2 weeks 1 day ago #26488

Still hoping for some answers if at all possible (being
lazy about examining the code ;-)).

My questions for the developers are: is it possible to ask for the "southern
hemisphere" style rotation even if one is in the northern hemisphere?
Would that solve my problem when using a diagonal? If so, where
would I ask for such a feature? If not, is there something else I can
do to make this work? Or am I wrong altogether? (doesn't appear
so from the experiment).

Another thought is that, if I am at all correct (not a certainty), then
those trying to polar align using a typical SCT would also fail in
this way...

Thanks,

Greg

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Question on Polar Alignment Assistant 2 weeks 1 day ago #26489

Hello again all,

OK, embarassingly, I think I have to say, "Never mind..." :-)

In the last tab marked "Controls" for the ASI camera I am using,
there is, right there, a value for a parameter called "flip".
All I have to do is remember to set that to 1 when doing polar
alignment -- it was set to zero by default. (1 = horizontal flip)

Problem solved!

Greg

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Question on Polar Alignment Assistant 1 week 5 days ago #26517

As a final entry on this thread, I report that the accommodation
that I mentioned previously (i.e., asking the camera driver to do
a horizontal flip, Control/Flip value == 1) did indeed work correctly
for me, in a test conducted two nights ago, and gave an excellent
polar alignment.

However, not all camera drivers have that option, or have it
presented to the end user as conveniently as is the case for
the ZWO/ASI driver. So, it would not be amiss for the developers
of Ekos to consider a switch that would change the alignment
calculation ("Invert Rotation Calculation" or some such appellation),
in order to accommodate those users who do not have such an
option with their cameras.

Greg

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Last Edit: by astronomerc.
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