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Another PHD2 Polar Drift Alignment tool


kens

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The latest dev5 version of PHD2 now includes two new PA tools: Static PA (SPA) and Polar Drift. The traditional Drift Alignment is the most accurate whilst the Polar Drift is very simple and SPA is fast. The two new ones align in the polar region rather than at the equator so may not be suitable for everyone. 

SPA has been around for a few dev releases whilst Polar Drift has just been released. Polar Drift is particularly useful if you want to align in the polar region but your polar alignment is a long way off e.g. due to a new setup. I use the tools as follows:

Do a rough manual alignment 
Point the scope near the pole (home position for a GEM)
Launch PHD2 and start the Polar Drift tool from Tools > Polar Drift Alignment
Select a convenient guide star and click Start
Wait until the "lollipop" settles down then click stop
You can read the PAE on the status line and adjust the guide star into the circle at the end of the lollipop

Once within about 10 arcmin I switch to SPA

In SPA it is important for the scope to be pointing accurately at the pole so the alignment stars are visible. For northerners Polaris is normally an easy target. In the south thinags are a bit harder so I proceed as follows:
Clear any star alignment/ sky model sync points from the mount - these can throw out the alignment process
Start the SPA tool from Tools > Static Polar Alignment
If the alignment stars are not visible, I pick any star and start the alignment. 
Ignore the adjustments and see if the centre of rotation (CoR) is in the FOV. If not, slew carefully in declination only to bring the CoR into the FOV.
If the previous Polar Drift was reasonably successful the alignment stars should become visible in the FOV
Then I follow the normal SPA process. 
Select an identified alignment star
Start the SPA process. If I have any problems I revert to the manual mode and slew manually
Adjust according to the on screen display

Once I'm within 5 arc minutes I confirm with a regular drift alignment and fine tune

Polar Drift.png

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I rather do not have a clear and open view towards POLARIS; Hence ! I must use the DRIFT METHOD in PHD2.. But PHD2 is for sure doing great progress and developing new  and interesting futures.. 

 

Regards

Martin

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Thats a good question. I've recently installed an OAG but haven't tried SPA with it. The distortion near the edge of the field may cause inaccuracy.

You could of course use the imaging cam if its a probem. You'd need to set up a new profile in PHD2 and calibrate it first. I've used my ASI1600 cam for that purpose. I also bin the camera 4x4 as otherwise PHD2 has trouble processing the large number of pixels.

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9 hours ago, kens said:

Thats a good question. I've recently installed an OAG but haven't tried SPA with it. The distortion near the edge of the field may cause inaccuracy.

You could of course use the imaging cam if its a probem. You'd need to set up a new profile in PHD2 and calibrate it first. I've used my ASI1600 cam for that purpose. I also bin the camera 4x4 as otherwise PHD2 has trouble processing the large number of pixels.

 

Thanks for the answer, I hadn't even thought about using the main camera. I guess I could set a large search area and use subframe download to speed it up on that profile, I'd have thought bin x4 would lead to inaccuracies due to the huge pixels, but what do I know ?

 

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With an Atik 460EX at 1200mm your pixel scale at 4x4 binning is still only 3" per pixel. But seeing as it is "only" 2749 pixels across you would only need to bin 2x2.  And in any case, SPA takes into account the pixel scale when it calculates how much to rotate in order to detect the deviation of the arc from a straight line. Smaller pixels need less rotation and speed up the process. But they can have their own problems as poor seeing and errors in the mount have a greater relative impact.  

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