Need help for polarscope calibration for Skywatcher AZ-EQ6 Mount

[Muse]

I am a newbie who now struggles with calibrating the polarscope of my newly bought SW AZ-EQ6 Pro mount. Following some Youtube advices, I centred a distant object on the reticle, and found some gap between the object and the centre when I turned around the shaft 180 degrees. I tried to calibrate it by turning the three screws as advised. But the object image would move father and farther away from the centre. Judging from that right turn screwing has reached the limit on all three screws and left-turn screwing is the only option left but leading to the increasing gap, am I right in thinking that the reticle has dropped inside? I remember that I had turned around the screws mistakenly for trying to solve another problem a few day ago. If I have to take out the whole polarscope to reset the reticle inside, will it be technically too demanding for people like me who has useless fingers?  Your advice will be greatly appreciated.

[mikeyj1]

It's been awhile since I did it, but those 3 screws effectively sit on the edge of the reticule glass. So it's a combination of loosening 1 or 2 and tightening the 3rd to move it in the direction you want to go (half the error distance from rotating the RA axis 180°). If the reticule has become dislodged through over loosening, you can sometimes reseat it without removal, 1st of all and screw the focusing lens at the front and you should be able to see the reticule. You might need to balance the mount so that the polar scope is looking downwards  or upwards (I can't remember which way the reticule sits on the flange), jiggle it so that it re-seats and then gently tighten the screws up evenly. Once you got it all back together you can repeat the polar scope alignment routine but this time only move it in small steps to make sure it does actually move in the direction you want to go.  It always used to annoy me that the reticule isn't captive so that the lines point vertical when in the home position, but whilst you're doing this, you can get it close (dont touch the glass with a finger, you'll leave a mark), or just ignore it..it still works but in a different position.  If all else fails, you can take it apart, but try not to first of all

cheers

Mike

 

[Seelive]

 ... and found some gap between the object and the centre when I turned around the shaft 180 degrees...

Do you mean it didn't remain on the graticle circle when you rotated the RA axis or it moved off the circle centre? The adjustments required are quite fine, just a quarter turn on the grub screws makes a big difference.

My mount had cone point grub screws which tended to 'dig' into the graticule mount making fine adjustments difficult. I replaced them with cup point which made accurate alignment much easier. 

[Muse]

Hi Seelive, I meant that when I rotated the RA axis, the image moved away from the previously focused centre, a symptom that I need recalibration.

Yes, perhaps I overscrewed them and something went wrong. 

[Muse]

Mike, that seems to be the only solution at this point. I will try it under daylight tomorrow. You seem to have gone through the same problem. I will report the result tomorrow. 

[Muse]

I did it  this evening, because I couldn't wait until tomorrow. When I unscrewed the focus lens, I could see what was happening inside in its entirety. Truly, the three screw system is absolutely unergonomic I suppose. Anyway I solved the problem. Many thanks, Mike, and thank you also Seelive, for your kind comments.