[g__day (Matthew)]

Folk I'm interested in fixing that last bit of polar misalignment I am seeing on a permanently mounted rig (Atlux on a pier in an astrolab). At my disposal are the latest versions of MaxPont, PEMPro and Tpoint for the Sky 6 - and plenty of time.

I guess my polar alignment is within 1-3 arc minutes of the SCP (true versus refracted SCP - I don't know).

My main scope is a C9.25 with a Canon 400D on it. I use the central focus spot on the Canon viewfinder to centre my stars when aligning (shining a very small red led into it so I can see this spot when its otherwise pitch black! Finally I assume my C9.25 has some very slight mirror shift that changes based on elevation or other random factors. Being Carbon fibre my focus rarely changes night by night. I have a starlight fine focuser on the SCT (greatly helps remove any mirror shift) - but I focus using a Meade motorfocuser into a JMI PC controller and a Bhatinov mask. So Once I'm set up and focused - I never physically touch the mount or scope during the night's run (so rule out human errors from knocking gear). The OTA is firmly attached using Losmandy bars - so I assume there is minimal differential flex happening via the mounting rails.

Last time I checked with multiple 30 minute runs on PEMPro on both Alt and Az - it said I was aligned with 0.2 arc minutes of the SCP.

MaxPoint with a 80 star model says I'm 25 arc seconds too low and around 3 arc minutes West of the SCP.

Tpoint with a 70 point star model says I need to rotate the mount 4.7 minute to the East (Sigma 93.987)and elevate it -2.1 minutes (Sigma 95.899) (which I guess means drop it 2.1 arc minutes - which would be disagreeing with MaxPoint)?

So lovely - three modern pieces of software - all purpose built to aid polar alignment - all disagree!

Oh the Hand controller itself - a SkySensor2000-PC Final version EPROM - set to polar aligned mode. Interesting behaviour when I do an initial 3 star alignment from mount level and facing East. I generally align on a triangle of stars Achnerar, Dipha and finally Rigel Kentarus - always in that order - always twice - one pass through alignment followed by the next. Once I have a two star alignment and slew to Rigel Kentarus the first time (before 3 star alignment is reached) the mount always stops pointing about 1-2 arc minutes too far West and 1-2 below my target. I am pondering if this closing error on my 3rd star is a very good indication of my polar mis-alignment error. If my mount overshoots the third star to the West by say 2 arc minutes - sounds to me my starting position was too far West to begin so I have to rotate my mount 2 arc minutes to the East - agreeing with Tpoint. Similarly if my mounts end up too low on the thrid star does that mean it started too low by this inverse amount?

If I was using a large refractor - I guess I could rule out any mirror shift during drift alignment - by eye or using PEMPro. As this is not the case I am pondering is this why I see three modern pieces of software giving conflicting advice.

I am tempted to rotate the base of the mount 2 arc minutes to the East then doing a 3 star alignment on the hand controller and noting if homing to the 3rd alignment star becomes a lot more precise. Then I could repeat the exercise in Altitude.

Can I ask for advice - why what you do in my place to nail the final polar alignment tuning? Do I trust Tpoint over the rest of the software and or the SkySensor2000-PC hand controller itself?

Thanks,

Matthew