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Old 24-09-2014, 12:35 PM
johnnyt123 (John)
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polar alignment mystery

Hi guys...

took advantage of the clear nights we have had here in sydney recently and this was my latest polar alignment effort with a Heq5 pro.

Is this typical of what can be achieved with this mount if can it be bettered?
Its difficult to make very minute adjustments with this mount.
also something i have noticed is that there is a difference in the alignment accuracy reading when you select different alignment star.
an one other thing, why is it that the 3rd star to align with is always way out when the first 2 are more or less spot on?? I would have assumed all 3 stars to be more or less at the center of the bullseye being so close to true polar alignment
has anyone else experienced this??

my main concern is....is my degree of alignment sufficient for 15-20 min exposures? it is very difficult to get better alignment than that with a Heq5 pro.

regards

John
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Old 24-09-2014, 02:58 PM
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rustigsmed (Russell)
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hi john,

have you tried for 15-20min subs? I think it will probably be ok.

yes mine changes depending upon the stars. I've had all zero's across the board a few times, whether or not that is actually a reality is another question all together.

I know there are some people who go with the 3 star alignment process but I use 2 star alignment. From memory the manual suggests 3 star alignment to make a more accurate map of a certain part of the sky and to help eliminate cone error.

cheers

rusty
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Old 24-09-2014, 03:18 PM
PeterEde (Peter)
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Question
If we're aligning to the SCP that for many is hard enough to pickout and drift aligning is a mystery still
Why can't we just centre a star. set mount to those coordinates then when setting back to centre shouldn't the SCP be there?
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Old 24-09-2014, 03:51 PM
johnnyt123 (John)
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Quote:
Originally Posted by PeterEde View Post
Question
If we're aligning to the SCP that for many is hard enough to pickout and drift aligning is a mystery still
Why can't we just centre a star. set mount to those coordinates then when setting back to centre shouldn't the SCP be there?
That would work for alt-az mounts. where the orientation of the mount does not matter. the mount tracks in 2 axis.

with an equatorial mount only tracks about 1 axis (RA axis I believe)
so that means that axis needs to be polar aligned as the mount assumes it is

In order to track an object on a mount that is not polar aligned, the mount will need to track in 2 axis and this is what an autoguider does by sending pulses to both RA and Dec axis to correct for errors in alignment.

hope that helps...

regards John
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Old 24-09-2014, 03:57 PM
johnnyt123 (John)
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Hi Rusty..

I used to align with 2 stars but when i was close to believing i was polar aligned, i would align with 3 stars and everything never as it seemed....alignment was definately not the same as was indicated by 2 star alone.

I tried 20 min subs last night for the first time...the stars at the edge were marginally elongated...
I am not a big fan of aligning the Heq5 pro...it isnt bery user friendly especially the elevation axis....

Is there some sort of plate that can be mounted between the tripos and mount head that is motorised and can be used to uncrimentally move the mount head in alt az for accurate polar alignment?

hmmm i am not sure if i should move this thread to equipment discussion....

John
Quote:
Originally Posted by rustigsmed View Post
hi john,

have you tried for 15-20min subs? I think it will probably be ok.

yes mine changes depending upon the stars. I've had all zero's across the board a few times, whether or not that is actually a reality is another question all together.

I know there are some people who go with the 3 star alignment process but I use 2 star alignment. From memory the manual suggests 3 star alignment to make a more accurate map of a certain part of the sky and to help eliminate cone error.

cheers

rusty
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Old 24-09-2014, 04:12 PM
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rustigsmed (Russell)
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Quote:
Originally Posted by johnnyt123 View Post
Hi Rusty..

I used to align with 2 stars but when i was close to believing i was polar aligned, i would align with 3 stars and everything never as it seemed....alignment was definately not the same as was indicated by 2 star alone.

I tried 20 min subs last night for the first time...the stars at the edge were marginally elongated...
I am not a big fan of aligning the Heq5 pro...it isnt bery user friendly especially the elevation axis....

Is there some sort of plate that can be mounted between the tripos and mount head that is motorised and can be used to uncrimentally move the mount head in alt az for accurate polar alignment?

hmmm i am not sure if i should move this thread to equipment discussion....

John
could be cone error?
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Old 24-09-2014, 05:30 PM
PeterEde (Peter)
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Quote:
Originally Posted by johnnyt123 View Post
That would work for alt-az mounts. where the orientation of the mount does not matter. the mount tracks in 2 axis.

with an equatorial mount only tracks about 1 axis (RA axis I believe)
so that means that axis needs to be polar aligned as the mount assumes it is

In order to track an object on a mount that is not polar aligned, the mount will need to track in 2 axis and this is what an autoguider does by sending pulses to both RA and Dec axis to correct for errors in alignment.

hope that helps...

regards John
I am basically polar aligned. I'm just hunting that sweet spot. Just was thinking if my mount is so close that I could set on a star and do as I said. It would get pretty damn close I thought??
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Old 24-09-2014, 05:40 PM
johnnyt123 (John)
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That sounds like a 1 star alignment procedure....

Unless I misunderstood you there...


Quote:
Originally Posted by PeterEde View Post
I am basically polar aligned. I'm just hunting that sweet spot. Just was thinking if my mount is so close that I could set on a star and do as I said. It would get pretty damn close I thought??
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Old 24-09-2014, 07:00 PM
raymo
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John, The figures you posted show very good alignment, and you have reached a position of diminishing returns, where the time and effort
needed to improve them is not worth the very slight improvement in tracking. Firstly, if you have checked your cone error, and it is good,
stick to 2 star alignment as many of us do. When you talk about 15-20
minute subs, this is meaningless because the possible length of subs
depends on several factors which are different for different people.
Unguided subs seem to be limited on a consistent basis with the HEQ5
to 2 to 2.5 mins using a 1000mm focal length scope. Short refractors
will obviously get a lot longer than that, and unreduced SCTs will get
a lot less.
Guided subs are limited by Focal length, guidescope flexure,
atmospheric conditions, light pollution, quality and sensitivity of the
autoguider, and how well it is set up, or manual guider's concentration, experience of the operator, and the list goes on. Unless you operate
your scope from a nice dark site your subs would be washed out well
before 15-20 mins anyway.
Peter, locking on a single star does not work well for the same reason that you have to triangulate to find your position on earth. The
computer would obviously know where the target star is, but it could not locate itself, because it would not know from what direction it was looking at that star.
raymo
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Old 25-09-2014, 09:08 AM
johnnyt123 (John)
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What are we looking at there Nico...

It looks like sky safari perhaps?
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Old 25-09-2014, 09:40 AM
PeterEde (Peter)
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The CSP. Off centre by a poofteenth by the image I did last night
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Old 25-09-2014, 10:34 AM
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Quote:
Originally Posted by johnnyt123 View Post
Hi guys...

took advantage of the clear nights we have had here in sydney recently and this was my latest polar alignment effort with a Heq5 pro.

Is this typical of what can be achieved with this mount if can it be bettered?
Its difficult to make very minute adjustments with this mount.
also something i have noticed is that there is a difference in the alignment accuracy reading when you select different alignment star.
an one other thing, why is it that the 3rd star to align with is always way out when the first 2 are more or less spot on?? I would have assumed all 3 stars to be more or less at the center of the bullseye being so close to true polar alignment
has anyone else experienced this??

my main concern is....is my degree of alignment sufficient for 15-20 min exposures? it is very difficult to get better alignment than that with a Heq5 pro.

regards

John
VERY good polar alignment.

As to imaging, I have done 20 minute subs with an alignment worse than that (even up to a minute off) and the autoguider wasn't even fighting very much.

Just give it a go and see how it works. A lot depends on a good alignment, but more depends on how well the mount tracks and how it responds when corrected for errors. I have had a former NEQ6 almost spot on polar aligned, but because of poor adjustment, tracked TERRIBLY and 5 minute subs were all it could/would handle without problems.
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Old 25-09-2014, 11:06 AM
johnnyt123 (John)
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yes of course...

that raises the question...

could you polar align a Heq5 pro via the following method..

Usind a ccd camera...
Parking the scope and manouvering the mount only to place the CSP in the center of the frame..??

The only problem i see here is that the scope may not be 100% parallel to the polar axis of the scope...

John
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Old 25-09-2014, 11:46 AM
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Sorry guys,
All the text I posted vanished and it was the wrong picture anyway.
I'll start again as it was late when I posted last night and it obviously went wrong.
I have very good success with the method of one star goto, physically align the mount with the Az and Alt screws on the mount on the chosen goto star eg Alpha Crux or something similar distance from the pole in the East or West and at around 45 deg altitude.
I then Park the scope and check for my pole stars, there are three of them and the main one is "BQ Oct" this little red star and the two faint stars to the left point directly at the SCP and so when I can see these in the PHD image I make fine adjustments on the mount Alt and Az screws to centre the SCP in my view and I'm done.
From there on I can goto any target and it will be in the field of view and if I want more accuracy I will sync on a few stars as I go, I drive the mount with the lappy and TheSky6.
You need to have your guide scope and main scope aligned with each other and the RA axis of the mount pretty well and that's the secret to this method.
I am fortunate that my main scope camera and my guide scope camera have a very similar field of view and so when I use PHD2 I can see these three stars quite well and it also helps when framing a target as I have the frame marked in Sky Safari Pro and also in TheSky6 so I can see before I start imaging what I'm going to capture.
This method saves a lot of time when you have to setup every time you go out as I do, no Obs unfortunately.
Hope this makes a bit more sense than the previous post.

PS. Obviously the 38 deg line won't be where you find the SCP unless you're at the same latitude as me.
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Old 25-09-2014, 02:21 PM
johnnyt123 (John)
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I think what we need is a camera through the polar scope.
and a polar scope that is well made and highly accurate.
The one i have in my Heq5 is all over the place. too many things that move and are adjustable......
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Old 25-09-2014, 04:31 PM
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Nico13 (Ken)
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Quote:
Originally Posted by johnnyt123 View Post
I think what we need is a camera through the polar scope.
and a polar scope that is well made and highly accurate.
The one i have in my Heq5 is all over the place. too many things that move and are adjustable......
I have never really fussed with the Polar scope to tell the truth, once I was happy that scopes were as close as I could get them to be aligned with the RA axis that was it because I run a side by side rig with the RC8" and ED80 that are removed and refitted every time out I left it all alone.
I have a good solid Losmandy plate to mount to and I had re-machined the EQ6 dove tail make sure it was accurate and everything went back in the same place each time and have had no issues.
On a clear staedy night PHD reports +or- 1 arc sec guiding any further improvements would require the mount be stripped down and tuned up.
what I did do with the ST80 guide scope is permanently fix it to the middle of the side by side plate inbetween the other scopes to minimise any errors being introduced with removing it each time.
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Old 25-09-2014, 07:07 PM
raymo
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Most people don't bother with the polar scope in the Southern hemisphere. It has to be adjustable, so it's not the poor HEQ5's fault.
The not 100% parallel to the polar axis that you mention is the cone error
that others have mentioned.
raymo
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Old 25-09-2014, 07:26 PM
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Quote:
Originally Posted by johnnyt123 View Post
I think what we need is a camera through the polar scope.
and a polar scope that is well made and highly accurate.
The one i have in my Heq5 is all over the place. too many things that move and are adjustable......
Steve Massey at myastroshop.com.au has an adapter to fit a GSTAR video camera to the polar scope so as to use it. Though, the HEQ5 and NEQ6 polarscope is tantamount to useless.

The polarscopes in the Vixens and Takahashi mounts work VERY well, with many users being able to polar align VERY accurately using the scope. I have never tried, as I have a snowflakes chance in Hades of seeing ANYTHING like Sigma Octans in my light pollution
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Old 25-09-2014, 09:01 PM
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Lewis, to be fair, you are comparing a Ferrari to a Toyota 86. The Tak
polar scope is probably the best part of the price of a complete HEQ5.
It's all academic in my case anyway; I would struggle to get down low
enough to look through mine.
raymo
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Old 26-09-2014, 10:29 AM
johnnyt123 (John)
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so it would seem that my polar alignment is ok but now gotta fix this cone error problem i never knew existed....

other than wedging between the dovetail and mount and finding the CSP in the eyepiece...is there anything else i can do?
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