Polar aligning from ANY part of the sky

Using SharpCap's Polar Alignment feature
AussieHowie
Posts: 25
Joined: Fri Aug 11, 2017 12:23 am

Re: Polar aligning from ANY part of the sky

Post by AussieHowie » Tue Apr 28, 2020 2:50 pm

The iOptron hand control has a PA routine built into it. Look for it in your manual. No need to see the pole to use it. You iterate between two stars you can see as East as possible and as West as possible - if memory serves me correctly. Club members get close enough that autoguiding with both DEC and RA pulses allows them 5 minute frames at high mag without any problems. Very quick to do that iteration too.

If anyone is reading this thread and has Orion or Skywatcher or Celestron eq mounts .... they too all have built in PA routines within the standard hand control menu. I have both Celestron and Skywatcher and used the built in PA routine on the hand control for years. Do 2 or 3 star alignment (which in effect creates the star map of the sky - like the OP using platesolve to do the same). Then you start the PA menu item which asks you to select a star you can see from your location, it slews to that star then asks you to centre that star in the FOV (of camera or EP). After that it slews slightly off target and prompts you to re-centre using the AZ bolt. Then it slews off target slightly again and prompts you to centre using the ALT bolts .... and you are polar aligned. Do a 1, 2 or 3 star alignment and away you go. I've gone 2min 20 sec unguided and 10 minute subs guided at 1000mm with 11mm sensor.

Also, there is another Iterative polar alignment technique different to that which iOptron use. Again no need to use any stars near the pole ... even though most do. It works best with the first star being somewhere on the celestial equator and the second being either as far north or as far south as you have available and also best if there is 3 hours difference in RA between each star. You pick two stars you can see. Slew to whichever is closest to the celestial equator and "sync" on it. Then slew to the other star further N or S where you correct HALF the error using the ALT and AZ bolts. After 3 or so iterations between those 2 stars (which is pretty quick to do) you will be very closely polar aligned. Easily go 5 minutes sharp stars with DEC and RA guiding. Where I said that you SYNC on the first star ... that is the Celestron SYNC process, most other mounts have something similar such as Precise GoTo (Skywatcher and Orion). Or if unsure about SYNC'ing etc just use a 2 star alignment whereby when you slew to the first star centre using the direction buttons and when it slews to the second star in the 2 star alignment process then correct half the error using the AZ and ALT bolts .... IE the same end result iterating between the two stars but using 2 star alignment routine instead of SYNC or Precise GoTo.

As per other posts above, if you use autoguider to do both RA and DEC you really do not have to be that closely polar aligned. The guider pulses will sort it out for you. You can be several minutes (!) in PA error and not have any problems doing 5 minute subs with autoguider on DEC and RA.

Oh yeah .... I used to use the DARV method on my fully manual Star Adventurer ... Google Drift Alignment Robert Vice DARV for yet another way to do drift aligning which does not require a view of the pole, just of stars on the celestial equator. The originator says its faster than normal drift aligning but trust me it is still quite tedious. But there you go .... use it if you like the look of that one.

BTW every single PA routine including polemaster, sharpcap, iterative, DARV, AllStar etc all require you to do a star alignment after doing the PA ... as by adjusting the AZ and ALT bolts during the PA process you have moved the mount away from its original pointing model (broken its star alignment if you did one beforehand). I said IF you've done a star alignment beforehand, because that's one of the beauties of polemaster and sharpcap in that no alignment is necessary beforehand! I put my workflow down below.

Having stuffed disks in neck and back and use cameras for everything (no EP's) I've tried them all. Nothing beats polemaster or sharpcaps implementation of the same PA technique. Setup is super easy using either.
1. No leveling of the tripod required.
2. Stick on the mount and OTA and balance. No need to power up at this point!
3. Use RA clutch to tilt over 45 degrees to the left and start the PA routine on your laptop. Do step one. Then again use RA clutch to then tilt 45 degrees over to the right (thus making the required 90 degree RA rotation). Do remaining adjustment of AZ and ALT bolts in the PA routine. Done! You are now polar aligned in about 3 minutes.
4. Use RA clutch to roughly put OTA into HOME position then power up the mount entering your lat long and date and time,etc.
5. Perform a 1, or 2, or 3 star alignment depending on how accurate you want your go to's to be and you are up and running.

Cheers

Juicy6
Posts: 4
Joined: Sat Apr 25, 2020 6:30 am

Re: Polar aligning from ANY part of the sky

Post by Juicy6 » Wed Apr 29, 2020 6:10 am

AussieHowie wrote:
Tue Apr 28, 2020 2:50 pm
The iOptron hand control has a PA routine built into it. Look for it in your manual. No need to see the pole to use it. You iterate between two stars you can see as East as possible and as West as possible - if memory serves me correctly. Club members get close enough that autoguiding with both DEC and RA pulses allows them 5 minute frames at high mag without any problems. Very quick to do that iteration too.
Wow! I have missed this totally. They call it BrightStar Polar Alignment. I will try it next night out. Thank you for reminding us of this (not widely known) function!

Christer, Sweden
Sky-Watcher Esprit 100 ED Super APO
ZWO ASI 294 MC Pro
ZWO ASI 120MM on a QHY Mini guider
iOptron CEM40

mikeykokomo
Posts: 1
Joined: Thu May 21, 2020 3:13 am

Re: Polar aligning from ANY part of the sky

Post by mikeykokomo » Sun May 24, 2020 4:39 am

AussieHowie wrote:
Tue Apr 28, 2020 2:50 pm
The iOptron hand control has a PA routine built into it. Look for it in your manual. No need to see the pole to use it. You iterate between two stars you can see as East as possible and as West as possible - if memory serves me correctly. Club members get close enough that autoguiding with both DEC and RA pulses allows them 5 minute frames at high mag without any problems. Very quick to do that iteration too.

If anyone is reading this thread and has Orion or Skywatcher or Celestron eq mounts .... they too all have built in PA routines within the standard hand control menu. I have both Celestron and Skywatcher and used the built in PA routine on the hand control for years. Do 2 or 3 star alignment (which in effect creates the star map of the sky - like the OP using platesolve to do the same). Then you start the PA menu item which asks you to select a star you can see from your location, it slews to that star then asks you to centre that star in the FOV (of camera or EP). After that it slews slightly off target and prompts you to re-centre using the AZ bolt. Then it slews off target slightly again and prompts you to centre using the ALT bolts .... and you are polar aligned. Do a 1, 2 or 3 star alignment and away you go. I've gone 2min 20 sec unguided and 10 minute subs guided at 1000mm with 11mm sensor.

Also, there is another Iterative polar alignment technique different to that which iOptron use. Again no need to use any stars near the pole ... even though most do. It works best with the first star being somewhere on the celestial equator and the second being either as far north or as far south as you have available and also best if there is 3 hours difference in RA between each star. You pick two stars you can see. Slew to whichever is closest to the celestial equator and "sync" on it. Then slew to the other star further N or S where you correct HALF the error using the ALT and AZ bolts. After 3 or so iterations between those 2 stars (which is pretty quick to do) you will be very closely polar aligned. Easily go 5 minutes sharp stars with DEC and RA guiding. Where I said that you SYNC on the first star ... that is the Celestron SYNC process, most other mounts have something similar such as Precise GoTo (Skywatcher and Orion). Or if unsure about SYNC'ing etc just use a 2 star alignment whereby when you slew to the first star centre using the direction buttons and when it slews to the second star in the 2 star alignment process then correct half the error using the AZ and ALT bolts .... IE the same end result iterating between the two stars but using 2 star alignment routine instead of SYNC or Precise GoTo.

As per other posts above, if you use autoguider to do both RA and DEC you really do not have to be that closely polar aligned. The guider pulses will sort it out for you. You can be several minutes (!) in PA error and not have any problems doing 5 minute subs with autoguider on DEC and RA.

Oh yeah .... I used to use the DARV method on my fully manual Star Adventurer ... Google Drift Alignment Robert Vice DARV for yet another way to do drift aligning which does not require a view of the pole, just of stars on the celestial equator. The originator says its faster than normal drift aligning but trust me it is still quite tedious. But there you go .... use it if you like the look of that one.

BTW every single PA routine including polemaster, sharpcap, iterative, DARV, AllStar etc all require you to do a star alignment after doing the PA ... as by adjusting the AZ and ALT bolts during the PA process you have moved the mount away from its original pointing model (broken its star alignment if you did one beforehand). I said IF you've done a star alignment beforehand, because that's one of the beauties of polemaster and sharpcap in that no alignment is necessary beforehand! I put my workflow down below.

Having stuffed disks in neck and back and use cameras for everything (no EP's) I've tried them all. Nothing beats polemaster or sharpcaps implementation of the same PA technique. Setup is super easy using either.
1. No leveling of the tripod required.
2. Stick on the mount and OTA and balance. No need to power up at this point!
3. Use RA clutch to tilt over 45 degrees to the left and start the PA routine on your laptop. Do step one. Then again use RA clutch to then tilt 45 degrees over to the right (thus making the required 90 degree RA rotation). Do remaining adjustment of AZ and ALT bolts in the PA routine. Done! You are now polar aligned in about 3 minutes.
4. Use RA clutch to roughly put OTA into HOME position then power up the mount entering your lat long and date and time,etc.
5. Perform a 1, or 2, or 3 star alignment depending on how accurate you want your go to's to be and you are up and running.

Cheers
AussieHowie's post is very informative. I give it an "A". Thank's mate.

In my ignorant opinion however (as I am a beginner) the sky model affects the go-to accuracy and not the tracking performance. Since guiding accuracy depends on polar alignment over time, a static or even drift alignment cannot compensate for leveling error, when present in both the longitude and latitude orientation. Leveling error, if present in both longitude and latitude orientation, will result in RA and Dec axis interaction. When RA correction is made under auto-guiding, an unintended Dec movement would occur. I understand that excluding leveling should not be included in a session's workflow. doing it accurately would be too time consuming. For those placing their mount head on a pier, accurate leveling will make a very significant impact and therefore should not be minimized.

My comments regarding the sky model should not be interpreted as criticism toward SharpCap's polar alignment tool. I believe it is scientifically sound and use it consistently. Guiding performance depends on polar alignment, leveling error and periodic error correction ... in my ignorant opinion.

Cheers, Mike

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