ChrisMoses

On 5/18/2014 at 17:03, frugal said:

The weather has finally cleared enough that I can actually use the scope the I bought in the FLO clearance sale a while ago. I spent a good while setting up the scope in the light. I collimated the polar scope and when it got dark I polar aligned as accurately as I could.

When I performed a two star alignment it reported a polar alignment error of about 1 arc minute in either axis. Seeking across to targets got them on screen first time every time.

My question is: Is a polar error of 1 arc minute considered accurate?

About half of the 150 second subs had nice round stars, however the other half had eggy stars (but I think that this had more to do with the balance being slightly camera end heavy)

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I just wrote a little calculator based on Barrett's paper.  It will let you calculate how accurate your PA needs to be given other parameters, including dec, guide star angle, and FL.

You can download it, and the source code in case you are a programmer, here:

https://github.com/133Parsecs/PolarAlignmentCalculator

There is a link to Barrett's paper at the bottom of the readme.

I hope it helps.

In general, 1 arc-min is very good. So good, in fact, I would question it if you just did a quick two star test.  My experience is that two star tests often do not give highly repeatable results.  I would try it a few times to be certain.  And be sure to use different stars.

Also, the required accuracy will change as you go higher in dec, or change your guide star. 

My routine is to try to nail PA as well as possible. Then I use a few minutes of drifiting in PhD2 to quantify it.  From there, I plug the parameters into the program and see what my max exposure time is for each target I'm thinking about imaging.

Hope that helps.

I haven't had a chance to read this entire thread yet, but it sounds fascinating.  If you still need beta testers, please let me know. I am an experienced developer and astrophotographer.