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Will exactly physically aligning telescope and polar-scope improve things?

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#1 meegja

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Posted 02 March 2021 - 11:34 AM

I have a Ioptron CEM25EC mount and an Ipolar Polar-scope. I did build it into the RA-axel of the mount.
Everything is working fine but (like almost everybody here wink.gif ) I want to have things almost exactly right.

 

So, does it matter that the polar scope itself is not exactly aligned with the telescope? I never checked this because all works just fine.

So on purpose, putting Polaris in the center of of the polar scope, must it then also be in the center of my telescope view?

Or is this a matter of "When it works then it's a matter of if it ain't broke, don't fix it"?


Edited by meegja, 02 March 2021 - 11:37 AM.

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#2 peta62

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Posted 02 March 2021 - 11:38 AM

No it does not. Polar alignment is to align the R.A. and Earth axis so the scope tracks object precisely. It has nothing to do with scope position.


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#3 bobzeq25

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Posted 02 March 2021 - 12:01 PM

Aligning something like an iPolar or a PoleMaster, or when using Sharpcap Pro is of _no_ importance.  The computer software compensates. 


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#4 dx_ron

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Posted 02 March 2021 - 12:03 PM

To add to what peta62 said: If you are using the polar scope for your alignment, you do want it to be aligned to the RA axis. You can check that by centering something in the small central circle of the reticle (either a star, Polaris often being handy, or a distant object in the daytime). Rotate the RA axis through 180 degrees. If the star/object stays centered, your polar scope is correctly aligned. If it wanders out of the small circle, the fix with CEM25 mounts is to adjust the position of the reticle. No point in linking the instructions here, because you probably don't need them and it isn't for the faint of heart (there is a pretty high likelihood of breaking something if you are not extremely careful).

 

If/once you start using software for polar alignment, it doesn't matter.


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#5 meegja

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Posted 02 March 2021 - 12:23 PM

Thanks all :)

So the polar alignment is clear. I indeed also use the software for alignment.
But if the telscope itself is off? I mean for example the dovetail which is attached to it, is off by a millimeter or so. The RA axel is then aligned bit the telescope itself is slightly off that axle. This of course is fixed by the star alignment and Goto or plate solving but still, the initial position is off.
I ask this all because I want to refine my tracking: I don't have/use guiding but the CEM25EC mount is SO precise in it's tracking that I can do now 420 second exposures with tracking only (this with an 8" f/10 SCT). So every advantage I can have, I take :)



#6 daveco2

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Posted 02 March 2021 - 12:40 PM

As others have said, polar alignment is separate from telescope pointing.  But it would be useful to have them aligned to at least within the field of view of the telescope, so that when you do 1 or 2-star alignment or use Goto, you can see the target on your camera.

And you can be reasonably certain about having a verification of plate solve.  Of course, you could use blind plate solve, emphasis on the word "blind".  Field Of View=SensorWidth/ScopeFocalLength  (in radians); 6 radians per 360 degrees.


Edited by daveco2, 02 March 2021 - 12:43 PM.

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#7 bobzeq25

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Posted 02 March 2021 - 01:04 PM

Thanks all smile.gif

So the polar alignment is clear. I indeed also use the software for alignment.
But if the telscope itself is off? I mean for example the dovetail which is attached to it, is off by a millimeter or so. The RA axel is then aligned bit the telescope itself is slightly off that axle. This of course is fixed by the star alignment and Goto or plate solving but still, the initial position is off.
I ask this all because I want to refine my tracking: I don't have/use guiding but the CEM25EC mount is SO precise in it's tracking that I can do now 420 second exposures with tracking only (this with an 8" f/10 SCT). So every advantage I can have, I take smile.gif

There can be an effect.  But even that is somewhat compensated by the software, through the rotation process.

 

If you're not taking advantage of guiding, you're worrying about the wrong things.  They're far less important than that.  Guiding corrects well for a _lot_ of errors, getting feedback on tracking from a guide star is a _very_ powerful technique.

 

There are good reasons why serious imagers mostly either guide, or use very expensive mounts.  It's fundamental.


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#8 meegja

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Posted 02 March 2021 - 02:34 PM

There can be an effect.  But even that is somewhat compensated by the software, through the rotation process.

 

If you're not taking advantage of guiding, you're worrying about the wrong things.  They're far less important than that.  Guiding corrects well for a _lot_ of errors, getting feedback on tracking from a guide star is a _very_ powerful technique.

 

There are good reasons why serious imagers mostly either guide, or use very expensive mounts.  It's fundamental.

Ah well, I am a human guider then (in a matter of speaking) smile.gif

In SharpCap I choose 1 star with the "bulls eye" overlay and zoom in 600%. Any deviation I correct manually: RA with user defined tracking rate, Azimuth (if needed) with the knobs on the mount. Once tuned in (takes around 30 minutes), I almost have to do nothing anymore, the encoders and real-time PEC of the CEM25EC are doing their job then.
But no guiding is a choice for me, for now. I like experimenting plus I learn way more now then when I would have started with guiding right away.


Edited by meegja, 02 March 2021 - 06:30 PM.


#9 peta62

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Posted 02 March 2021 - 05:41 PM

Being a human guider is fun, I have done it too, I like it. What worries me is manual knob turning, it has to shake the system and bring inaccuracies into the picture, could you use motor on Dec too ?


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#10 meegja

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Posted 02 March 2021 - 06:32 PM

Being a human guider is fun, I have done it too, I like it. What worries me is manual knob turning, it has to shake the system and bring inaccuracies into the picture, could you use motor on Dec too ?

That was an error. I did write DEC but that should have been Azimuth, corrected it :) That of course is just a tiny adjustment to correct polar alignment if needed.



#11 peta62

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Posted 02 March 2021 - 06:47 PM

That was an error. I did write DEC but that should have been Azimuth, corrected it smile.gif That of course is just a tiny adjustment to correct polar alignment if needed.

I see so you do not have to adjust that much, that is good.



#12 Tim

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Posted 02 March 2021 - 08:26 PM

Being a human guider is old school that’s what a lot of people did back in the days of film.
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#13 psandelle

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Posted 02 March 2021 - 08:30 PM

Being a human guider is old school that’s what a lot of people did back in the days of film.

No thanks! I did my time as a kid! grin.gif

 

Paul



#14 meegja

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Posted 02 March 2021 - 08:51 PM

Being a human guider is old school that’s what a lot of people did back in the days of film.

And .... ?

When it works, it works. I choose not to use guiding, so what?

I track for 420 seconds with pinpoint stars on a 8" f/10 SCT. I learn now and have fun and maybe later I'll do guiding ...


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#15 Tim

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Posted 02 March 2021 - 08:52 PM

And .... ?
When it works, it works. I choose not to use guiding, so what?
I track for 420 seconds with pinpoint stars on a 8" f/10 SCT. I learn now and have fun and maybe later I'll do guiding ...



#16 Tim

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Posted 02 March 2021 - 08:52 PM

And .... ?
When it works, it works. I choose not to use guiding, so what?
I track for 420 seconds with pinpoint stars on a 8" f/10 SCT. I learn now and have fun and maybe later I'll do guiding ...



#17 Tim

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Posted 02 March 2021 - 08:59 PM

And .... ?

When it works, it works. I choose not to use guiding, so what?

I track for 420 seconds with pinpoint stars on a 8" f/10 SCT. I learn now and have fun and maybe later I'll do guiding ...

and what?  nothing!   sorry.

 

I wasn't implying anything wrong or right about it.

 

just that that's what was done for many years previously that's how they did it with an eyepiece not a computer screen. I was pointing it out as many younger people may not be aware of that's how it was done in the old days. I think its great your doing it, perhaps not for me.

 

 

I am glad I dont have to manually do it. Everyone should give it a go perhaps appreciate what technology is doing for us and helping us just like goto telescope and polar alignment aids etc the Hobby continues to grow expand. I think that's a great thing and also important that we understand how we got to this point in my opinion and understand the technology used previously.


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#18 peta62

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Posted 03 March 2021 - 04:28 AM

I think this is again everybody's personal choice. There is the whole scale spanning from doing everything by myself ( hardcore old school includes film development ) to setting up, going to sleep and finding the results in the morning. The latter is no more a hobby for me, I have to include my work, being by the scope under the sky, but I fully understand people are different, including amount of free time, so it is preferred way for many. I like time to time look into the recticle eyepiece, correcting the tracing, feeling I am taking the picture. Also I do not need computer for this, so much less hassle with power sources.

And I do not see anything bad in the "old school" label.


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#19 meegja

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Posted 03 March 2021 - 06:53 AM

and what?  nothing!   sorry.

I wasn't implying anything wrong or right about it.

just that that's what was done for many years previously that's how they did it with an eyepiece not a computer screen. I was pointing it out as many younger people may not be aware of that's how it was done in the old days. I think its great your doing it, perhaps not for me.

 

I am glad I dont have to manually do it. Everyone should give it a go perhaps appreciate what technology is doing for us and helping us just like goto telescope and polar alignment aids etc the Hobby continues to grow expand. I think that's a great thing and also important that we understand how we got to this point in my opinion and understand the technology used previously.

Sorry, my bad then. I did read it as being down talked to. My apologies.


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#20 Tim

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Posted 03 March 2021 - 09:41 AM

Sorry, my bad then. I did read it as being down talked to. My apologies.

it used to be "bragging rights" to say how long one would look and guide for on a particular image. Somehow the image had more importance when someone would say I spent 2 hours on it. It was about the skill of the person guiding that helped create the image. I think its cool and likely gives one a good understanding of what the mount and equipment are doing second by second. 


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#21 SonnyE

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Posted 03 March 2021 - 02:05 PM

One thing about this sport is, the rules is: There is no rules.

Everybody seems to go about it in their own personal way, and interest.

I know I do. I came up through Budget Equipment. And Lordy, what a trial that has been.

But what ever way, and how ever done, we all fine tune our way through.

 

I know I'm a stickler for accuracy in what I do with my equipment.

If you try to do your best, you've done all you can do.

But tomorrow night might be even better.

So I might occasionally try to fine tune something to make it easier or better than I had it.

One of my more recent was to turn my Guide camera so its picture moved the same as my main telescope, for easier aligning.

 

I don't really think to much about it, but I'm always thinking and occasionally fiddling or tweaking things a bit.

I just figured it's part of the fun being down in the fishbowl looking up at the sky.


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#22 meegja

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Posted 03 March 2021 - 05:05 PM

It's gone a bit off topic here but that's okay :)
It looks like tracking vs guiding might be in the same realm as refractor vs reflector ;)
But yes, everybody does things in their own way.

I myself got my scope originally for planetary but very soon I went for deepsky and now I am mostly aiming for faint objects like planetary nebulae. All this as starter last year with a long focal length SCT and tracking only.

And I love it, it's right up my alley to work with this and proof to myself (and others, to be honest ;) ) that experimenting, solving problems and overcoming obstacles are key and each time a victory in itself.

But that's just me :)


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#23 Sacred Heart

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Posted 04 March 2021 - 08:59 AM

I have a Ioptron CEM25EC mount and an Ipolar Polar-scope. I did build it into the RA-axel of the mount.
Everything is working fine but (like almost everybody here wink.gif ) I want to have things almost exactly right.

 

So, does it matter that the polar scope itself is not exactly aligned with the telescope? I never checked this because all works just fine.

So on purpose, putting Polaris in the center of of the polar scope, must it then also be in the center of my telescope view?

Or is this a matter of "When it works then it's a matter of if it ain't broke, don't fix it"?

I know nothing about your mount or polar scope.  I;m speaking on principals / mechanics.  Your polar scope should be in alignment with your RA axis, it is machined into your mount and that is important.  Your scope may not be able to " perfectly align " with the polar scope because of the worm engagement or something.  Level your mount as best you can.  Leave tripod legs set in that position or mark the legs with a paint marker.  If you take your scope apart everytime mark where the scope sits in the saddle, mark where your weights are on the shaft.

 

Do you have polar alignment software??  If yes, great. Use it and adjust the mount to it.  If mount is used in a portable setting,  mark the ground. So you can place it back in the same spot. the more exact the better, pending on what you do with the mount.  Finding the ISS and tracking requires exact, finding M31 or M57 not so much.   

 

Now that you have polar alignment, all sky pointing accuracy.  Build you a pointing model over the whole sky, east and west.   Keep the model active in your mount.  Now you should have repeatability and reproducibility for that spot.

 

 

                              It works for me,     Joe


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#24 meegja

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Posted 04 March 2021 - 12:21 PM

I know nothing about your mount or polar scope.  I;m speaking on principals / mechanics.  Your polar scope should be in alignment with your RA axis, it is machined into your mount and that is important.  Your scope may not be able to " perfectly align " with the polar scope because of the worm engagement or something.  Level your mount as best you can.  Leave tripod legs set in that position or mark the legs with a paint marker.  If you take your scope apart everytime mark where the scope sits in the saddle, mark where your weights are on the shaft.

 

Do you have polar alignment software??  If yes, great. Use it and adjust the mount to it.  If mount is used in a portable setting,  mark the ground. So you can place it back in the same spot. the more exact the better, pending on what you do with the mount.  Finding the ISS and tracking requires exact, finding M31 or M57 not so much.   

 

Now that you have polar alignment, all sky pointing accuracy.  Build you a pointing model over the whole sky, east and west.   Keep the model active in your mount.  Now you should have repeatability and reproducibility for that spot.

 

It works for me,     Joe

Thanks for the remarks and tips!
Originally the CEM25EC mount comes with a normal see-trough polar finder. For me not handy since I'm 6ft7 tall, so I did build in the Ipolar camera myself according to the provided manual. There is some deviation because when I do the star alignment to build the GoTo model, the pointed stars are just outside my FOV. But, that POV is very small with my scope and camera: 41' 42" x 27' 42". But after star alignment (or plate solve with StarCap) everything works fine.
I do use the Ipolar software, version 2.21 in my case because I also have troubles with the latest versions of that.

And indeed I have a standard spot where I build up (my balcony), so I did mark the concrete where the legs are placed on anti vibration pads. This also evens out the small irregularities in the concrete.

 

I do not understand though what you mean with building a pointing model of the sky and keep that model active in my mount? Whenever I power off my mount, no such data is kept. Also, I have zenith to the horizon North to South-West. So no East at all sadly. Still I am not complaining with an almost 180 degrees free sky :)



#25 bobzeq25

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Posted 04 March 2021 - 04:18 PM

Pointing models are useful for making mount GOTOs more accurate.  Since I use platesolving to go to my targets, I have not used a pointing model (or a star alignment, which builds one) in years.  Platesolving is more accurate.


Edited by bobzeq25, 04 March 2021 - 04:19 PM.

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