pier-tech DDM85 and keeping polar alignment?

[prefetch]

i'm considering getting a pier tech extendable pier system, but i'm concerned that it would lose polar alignment and generally cause problems w/ the consistency from night to night w/ pointing files, etc.

 

i did a forum search and found a member that has one, and i sent him a PM, but he hasn't logged in for a month, so i thought i'd just post to see what people think about this idea.

 

i read this review which seems encouraging: http://www.pier-tech.com/polar_alignment_repeatability.html

 

the reviewer used a Tpoint model, which seems similar to our pointing file concept.

 

seems like i would just have to do a resync each night w/ autosequence to get autoslew back on track and creating a new pointing file would probably not be required.

 

thoughts?

[Roger]

I agree with your prognosis - but I stress it's only theory!

[wemartin]

Hi Prefetch,

 

I sent you a reply to your pm a couple of weeks ago.  Apparently you didn't receive it.  Here's the public version:  I have had no issues of pointing stability or polar alignment with my PierTech 3 pier mounted on a 2m reinforced concrete column.  The polar alignment is stable for many weeks at the level of repeatability of the Autoslew alignment procedure, about 0.2 arc min.  There might be long term variability but this could very well be due to the column moving with temperature.  One thing I do as a precaution is stop the pier raising to the very top limit of travel on the basis that the two columns of the PT3 may not be perfectly aligned.  The sacrifice of a centimetre or so of height is a bit of insurance.

 

So, basically you are more likely to change the polar alignment by changes to the OTA than I observe arising from the PT3.  Of course if you crash into the mount all the extra mechanical interfaces mean you are more likely to shift something than with a solid pier.

 

Bill