#1  
Old 09-05-2007, 09:07 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Polar Alignment

Hi All,

This is probably completely wrong, but...

If i got a celestron skyscout, put a laser on it and put it on a tripod. Then told it to point at the SCP.

Would this make it simple to polar align my NEXSTAR 11 assuming it was on a wedge. Pointing roughly south and so on.

I mean i could use the finder to align the laser dot to the center of the eyepiece using the wedge controls?

This is probably a dumb idea, so sorry
Reply With Quote
  #2  
Old 09-05-2007, 09:32 PM
Doug
Registered User

Doug is offline
 
Join Date: Mar 2006
Posts: 645
I could think of better ways to spend $700 if I already owned a nexstar 11.
A question.......what do you expect by way of pointing accuracy from your nexstar?
Reply With Quote
  #3  
Old 09-05-2007, 09:40 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Quote:
Originally Posted by Doug View Post
I could think of better ways to spend $700 if I already owned a nexstar 11.
A question.......what do you expect by way of pointing accuracy from your nexstar?
I am not using the Nexstar to point at the laser dot. I am using the wedge controls to align the mount. And you can get a seconhand sky scout for $450.

maybe?
Reply With Quote
  #4  
Old 09-05-2007, 09:44 PM
Doug
Registered User

Doug is offline
 
Join Date: Mar 2006
Posts: 645
After you have your nexstar polar aligned, what are your expectations for pointing accuracy or if you prefer, goto accuracy?
Reply With Quote
  #5  
Old 09-05-2007, 09:50 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Quote:
Originally Posted by Doug View Post
After you have your nexstar polar aligned, what are your expectations for pointing accuracy or if you prefer, goto accuracy?
Assuming it was correctly Polar aligned then i should get 10 minutes or more with guiding.

People take long exposures with Nexstars if they are correctly Polar aligned.


At least I think they do.
Reply With Quote
  #6  
Old 09-05-2007, 10:05 PM
Doug
Registered User

Doug is offline
 
Join Date: Mar 2006
Posts: 645
Well if you want a simple way of getting a polar alignment, (ball park) and you are having some difficulty with the SCP, you could always just 'goto a relatively bright object and then move/adjust your wedge to get the object in the EP. It is simply placing the cart before the horse. If you expect your nexstar to find an object once it is polar aligned, then it follows that once it thinks to is pointing to a known object, moving it till is is so pointing will place its polar axis close to the SCP. If you want it to track for 10 mins, you will need to drift align. I suspect that you have light polution probs that make viewing the SCP next to impossible?

edit cart/horse
Reply With Quote
  #7  
Old 09-05-2007, 10:24 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Quote:
Originally Posted by Doug View Post
Well if you want a simple way of getting a polar alignment, (ball park) and you are having some difficulty with the SCP, you could always just 'goto a relatively bright object and then move/adjust your wedge to get the object in the EP. It is simply placing the cart before the horse. If you expect your nexstar to find an object once it is polar aligned, then it follows that once it thinks to is pointing to a known object, moving it till is is so pointing will place its polar axis close to the SCP. If you want it to track for 10 mins, you will need to drift align. I suspect that you have light polution probs that make viewing the SCP next to impossible?

edit cart/horse
Thanks Doug,

I am new to Polar aligning and havnt actually tried it yet. I am about to buy a wedge and it seems very difficult to do, but i want to try. I was just thinking that by putting an actual dot in the sky exactly at the SCP then i wouldnt have to drift align as i would already be smack bang on the dot; or at the very least a bit of drift aligning around the dot.

So i am just asking this question to see if it is feasible or just a very dumb idea. I was kind of hoping a moderator would come and tell me if my idea was completely dumb or not .

You bet, i live 2km from the center of Sydney and it is very light polluted.

Paul
Reply With Quote
  #8  
Old 09-05-2007, 10:57 PM
Doug
Registered User

Doug is offline
 
Join Date: Mar 2006
Posts: 645
Paul I don't think your idea is crazy, just expensive. It should work in theory, but don't forget that sigma octans is not exactly on the pole anyway.

Where I am I have a large pine tree blocking a significant part of my southern sky such that I can not view any further south than about -70 dec. I wish I had a laser powerful enough to take out that pine tree, but I don't. So this is what I did.... first I did a 'goto' to the moon (about 1st quarter). I was probably about 10 deg or so out. I then moved the mount (pier and all)till the moon was in the EP. Then I parked the mount and did a 1 star alignment, and again moved the mount east/west and up/down till the alignment star was in the EP. The mount movements were of course mechanical movements; not using the RA or Dec motors. From that point I drift aligned till I had no drift.
Granted this method is not orthodox, but it works, and it does not rely on the SCP being visible from the place where the mount is placed. I should point out that my mount is set on a permanant pier, and therefore a different case to a portable setup. You might consider mounting a laser on your nexstar and after getting close to polar aligned, park the scope and use the laser to spot a point somewhere in your yard and take steps to be able to place your tripod close to the same place each night, then with your scope in park use the laser to position the mount to place the laser dot where your mark is and then quickly drift align. The more care you take initially, the less time will be wasted in susequent setups. Make sure your tripod is level (before the scope is placed on it. don't set up on bare ground. avoid changing the height of the tripod.
Reply With Quote
  #9  
Old 10-05-2007, 12:16 AM
ballaratdragons's Avatar
ballaratdragons (Ken)
The 'DRAGON MAN'

ballaratdragons is offline
 
Join Date: Jan 2005
Location: In the Dark at Snake Valley, Victoria
Posts: 14,412
I posted in here somewhere how I polar align very fast with a green laser, but I can't find it.

But this is how I do it:

1. Align my Laser and scope with each other using any bright star.
2. Then I make sure the scope is lined up with the mount (perpendicular) at 'Home' postion.
3. Find the Octans Trapezium in low power binocs (should be able to make it out in light pollution).
4. While keeping Octans Trap in binocs, reach over and turn laser on.
5. Adjust mount until laser is on the spot where the SCP is, then do final adjustment with Polar scope (if you have one).
6. Drift align if you wish. I don't bother as it is usually spot-on with the polar scope.

I have made some guides for you to point the laser at the SCP:

1. Octans box widefield so you can see where it is
2. Octans box and SCP location in low power binocs
Attached Thumbnails
Click for full-size image (SCP 1.jpg)
35.4 KB78 views
Click for full-size image (scp 2.jpg)
20.3 KB70 views
Reply With Quote
  #10  
Old 10-05-2007, 08:00 AM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Thanks Doug and Ken,

You have some really great ideas. Its very hard to imagine how i can easily do it until i get out and try. So when i get my wedge i will give both ideas a go; and get very frustrated no doubt.

Also how about this, with no laser.

Rough Alignment
(1) Set up mount, wedge make sure everything is level.
(2) Attach OTA and do a quick align.
(3) Tell scope to GOTO SCP and note where OTA is pointing
(4) Physically rotate mount and scope until front of wedge lines up with where the OTA was pointing in step 3. Make sure OTA is in home position.

Better Alignment
(5) Do a quick align then goto SCP again. (Scope is now tracking)
(6) Using wedge controls and low power eyepiece and Ken's diagram align scp in middle of eyepiece.

Final Alignment
(7) Using wedge controls and Ken's diagram align polar scope on SCP.


Dont know if the above would work, also i am unsure how to align the polar scope (which i dont have yet) and i guess if its not aligned to the mount then (7) wont be very accurate.

Maybe I am worrying about nothing, and will find drift alignment a piece of cake when i get out,.... but i dont think i will so i am a bit anxious.
Final alignment
Reply With Quote
  #11  
Old 10-05-2007, 09:36 PM
ballaratdragons's Avatar
ballaratdragons (Ken)
The 'DRAGON MAN'

ballaratdragons is offline
 
Join Date: Jan 2005
Location: In the Dark at Snake Valley, Victoria
Posts: 14,412
Paul,

Step 3 might be a bit hard considering the mount won't be pointing at the SCP to give any accuracy. So it probably won't point at the real SCP, only at what it thinks the SCP is from where your mount is pointing.

The polarscope should fit into the polarscope housing in the mount (if it has one). If it has, it will be accurate.
Reply With Quote
  #12  
Old 10-05-2007, 10:44 PM
Doug
Registered User

Doug is offline
 
Join Date: Mar 2006
Posts: 645
The Nexstars are as far as I know, all fork mounted jobs so a polar scope is out of the question.
Ken's method should work ok upto and including point 4.

The nexstar is a gps thing I believe and therefor might behave a bit differently from the Meade classic LX200. Assuming the gps can be turned off and the inbuilt electronic compass if it has one , turned off as well, the idea would be to start out with the forks level horizontally, and the ota set to -90 deg dec. then impliment Ken's method.

If you'd like to try mine, perhaps I should explain in a little more detail the rationale behind it.
With any polar mode 'goto' system, there are a number of assuptions made by the control electronics:
1. the polar axis is pointing exactly at the celestrial poles.
2. the correct siderial time + time zone offset have been entered.
3. the correct date has been entered.
4. the correct latitude and longitude have been entered.
Neglecting arguments about 1,2 or 3 star alignments,or no alignment,
lets just say that one star has been selected and the mount told it is aligned.
From this position the mount can calculate the movements needed to point to any selected object within range.
So now then, if I enter data in accord with points 2,3&4, I have only point 1 missing.
The mount knows no difference if I use a 1 star alignment and accept the position as correct, it will assume it is in fact pointing at the chosen alignment star even if it is in fact pointing in the opposite direction.
So if I now physically move the mount while it is still tracking, adjusting the altitude and the azimuth until the guide star is now in the EP, it follows that the polar axis must necessarily be pointing very close to the SCP, even if I was totally disorientated and began with the mount pointing north. In that case I would have to move the mount thru 180 degrees azimuth to get the star in the EP.
I had to use this method or else a more tedous meridian transit method because I simply can't see the SCP from my location, and there is too much ferous material nearby for a compass to work (from which to measure deviation).
Reply With Quote
  #13  
Old 13-05-2007, 09:15 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Thanks Doug,

I will definately try your method. I havnt got my wedge yet and am a bit anxious about if i can use it properly as polar alignment on an alt/az mount with wedge seems like a very arcane art.

When i look at some of the photos in the forums though i think it is something i very much want to learn.

My problem will be, my backyard is unsuitable so i have to go to a local park to setup. The isssue here is that is only 2km, maybe less from the center of Sydney and not many stars are visible.

Anyway, thanks for all your ideas, when i get my wedge and try it i will tell you how i go. I guess there is not much point talking about it, i need to get out and try.

Paul
Reply With Quote
  #14  
Old 14-05-2007, 12:01 AM
nightsky's Avatar
nightsky
Aus Irish Bi Cen Flag

nightsky is offline
 
Join Date: Mar 2006
Posts: 602
G'Day,
Not sure if this link will help you when you get your wedge as it's for a Meade LX 200 GPS,but who knows it's worth a look:
http://www.southern-astro.com.au/php...ralignment.php
Cheers
Arthur
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:37 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement