Star Adventurer Polar Alignment problem

[ariesram]

I am trying to figure out how accurate polar alignment should be in order to get a round star photo using certain lens and exposure time. 

calculated pixel size is about 15 arcsecs per pixel using my DSLR with 70mm lens on this website. 
https://starizona.com/tutorial/pixel-resolution-and-field-of-view-calculator/

Calculated alignment error using this tool. 
http://celestialwonders.com/tools/polarErrorCalc.html

Input drift 15 arcsecs, 1 minute, and declination 35 degrees, calculated alignment error is 69.95 arcmins, more than 1 degree. It is an error 
tolerance that allows rough polar alignment, isn't it? As long as Polaris is close to the mark that it is supposed to, there should be no 
trailing. 

I used this method to do polar alignment. Then verified the position of the 6 clock mark using PS align Pro. 
https://fstop138.berrange.com/2018/05/polar-alignment-of-the-skywatcher-star-adventurer/

I tested more than 10 times in different locations, and got good round stars 3 times using my Star Adventurer. All of rest is trailing ones. 
I could get round stars in one exposure, and all the following exposures are trailing stars. 

Polar alignment is as accurate as possible. I am sure that it's on Polaris, not other stars. 

No wind, solid Gitzo series 3 tripod on solid surface, shutter cable and remote control. Camera on DEC plate, no ball head. Properly balanced. 

I calibrated polar scope as per the process on the manual. It is good, too. 

I did a 24 hour test indoor. I marked a laser point on the wall 21'5" from the SA. 23 hour 56 minutes later the laser point was only 1 3/8" away. this is about 0.3 degree. 0.0002 degree per minute. 

Also I did a long exposure test of lights on horizon far away. No periodic error, no zigzag line of the lights. 

What can be wrong with the process? Does it tell that the SA is defect?
 

Thank you

Edited December 24, 2019 by ariesram

[Davey-T]

Hi and welcome to SGL.

If you do a continuous long exposure on a centred star do you get increasingly longer star trails ?

Dave