Polemaster - is it good?

[gregbradley]

I followed up on what the Polemaster was after seeing it in many thread titles.

Clever. It probably would not replace a TPoint model but it certainly sounds fast. Sometimes it would be good to confirm a T-Point model as I have had them be a bit off.

Anyone care to review the Polemaster? I imagine that 30 arc secs accuracy depends heavily on how well made the adapter is plus how well levelled the sensor is.

Greg.

[rally]

Greg,

I cannot imagine why any astroimager with Tpoint would be interested in using a tool that is at best 30 arc secs accurate when Tpoint is more like 1 arc sec !

Since Polemaster is also a self contained system - (camera & lens) - that means it needs to be added onto your imaging system - so there is yet another error to contend with - the difference between the alignment of the Polemaster and your imaging system

Tpoint is very accurate - If you had problems with Tpoint then I can only guess that there were problems with the mapping accuracy of the stars or movement/fexure in your system that wasnt being dealth with either mechanically or in software

Stick with Tpoint !
With accurately mapped stars I get reliable repeatability down to the arc sec.

[peter_4059]

There's a demo video of it on youtube. It looks like you rotate the RA axis as part of the routine so I suspect the alignment of polemaster with the mount axis is not critical. Its accuracy is another question though.

[gregbradley]

Tpoint has been good many times. It was the accurate polar alignment feature SB added to Tpoint. It has given me a worse PA at one point. I don't think I have ever seen accuracy to 1 arc sec. Sometimes a physical confirmation is superior to a modelled supposed polar alignment. I have had to use drift alignment a few times to correct a tpoint model. Sky X has occasionally had bugs in the southern hemisphere with regards to TPoint so its not bulletproof and infallible.

Greg.

[rally]

Peter,

The relationship between your telescope/imaging system and its alignment with the Dec axis (and RA) isnt being considered.
If the scope rings, optical axis, scope tube, mirror collimation is out - it doesnt know.

So even if they can eliminate the difference between the RA axis and the PoleMaster, its still not fixing a common problem that a full Tpoint model is designed to correct.
Even just using the 6 standard terms that Tpoint defaults to, will eliminate the most common errors that are probably in existence in almost every system. so it makes sense to use Tpoint still - even if you use PoleMAster as well !

I guess people can use whatever they like, but to discard a tool that not only provides an accurate Polar Alignment report well beyond the capability of the other option, but also goes on to correct (in software - using TheSky) all the normal geometric problems inherent in most systems and with a more expanded model, all the rest of the problems just seems retrograde.

These comments really applies only to systems using TheSky where the Tpoint model is fully integrated into the pointing and tracking control.

Ill try and find the video.

[peter_4059]

Rally, I never claimed the Polemaster was a substitute for a software program that takes care of all the errors in your mount and ota. I just said I don't think the accuracy of its attachment to the Ra axis is critical. Polemaster is intended for fast polar alignment. It never claimed to correct other mount and ota attachment issues.

[barx1963]

Here is a tutorial on using the PM

https://www.youtube.com/watch?v=0-9eHmd90tU

Not sure if it the one you referred to, a bit long winded (really do not care if his backyard is wet!) but it covers it's use.

Malcolm

[peter_4059]

That's the one I was referring to.

[garymck]

Hi,

Polemaster does not need to be accurately attached to a mount. It computes the center of rotation, and then shows you how to adjust based on that. This takes account of inaccurate mounting. Hence accurate mounting is not required. I've used it on a Celestron CPC, a Losmandy G11, an AZEQ6 and an EQ6. It never failed to give me a good polar alignment. It is nor arc second accurate - none of my scopes could be adjusted that well anyway!! I can't say how accurately as I don't hve the means to quantify it, but my dec drift is now all but non existent and better than a 4 hour drift alignment.

FWIW Gary

[gregbradley]

Thanks Gary.

There is something appealing about a physical method rather than a computed method. You are more in control for one thing rather than some behind the screen computation which may have errors in it.

My experience with Tpoint is overall quite positive, though as I have said its not always bullet proof as basic assumptions are made and they can be violated or the software has glitches in it which has happened a couple of times now that throw you off. And because that is hidden you may not pick up on it except for the clue from non round stars or guiding software showing drift is occurring.

Greg.

[Atmos]

I have personally found the best way to get results from Accurate Polar Alignment with my EQ6 is to, after every T-Point iteration, park and disconnect the mount and start again.

I set up every night and run 2-3 iterations of 26 point models. It may work very differently with a Paramount mount as they're designed to be completely integrated with TSX but after I have done the Accurate Polar Alignment I park and disconnect the mount (using EQMOD). After I reconnect I start a new model.

I have found that if I don't do this, for some reason the results on the next model can be very bad, even small moves can make it impossible to get an accurate PA.