importance of p.a. and alignment when plate solving and guiding

[iwols]

hi all going to try tortilla to plate solve and make it possible to revisit objects to add more data from various nights just wondered how important pa and alignment makes when going down this route as the plate solving would make any adjustments automatically with phd2 then holding the object centre thanks guys

[Demonperformer]

First thought is that, if PA is out, you will get field rotation on your subs.

[iwols]

cheers demon wouldnt i need to alter this on different nights and how my camera is set up on different nights anyway 

[wornish]

Having different field rotation from different nights shouldn't be a problem for most stacking software to handle.   DSS and PI both can handle quite large rotations or different alignments.

As long as the same camera is used CCD or DSLR on the same scope.

[Demonperformer]

From the replies, I'm not sure if you are getting what I was saying [apologies if you are]. When the PA is out, each individual sub will contain a certain amount of field rotation, resulting in some of the stars becoming streaks instead of points (and/or limiting the length of the sub). Certainly any slight variation in the postion angle of the camera from night to night can be sorted by the stacking software, but it generally can't turn stars that have streaked into single points. Neither can guiding software correct for this, unless you have a system that includes automated eyepiece-rotation [which, apart from being inordinately expensive, is, I understand, even more of a hassle than getting PA correct!].

[iwols]

thanks i think the answer is spend a little time and get pa  sorted first cheers all

[wornish]

20 hours ago, Demonperformer said:

From the replies, I'm not sure if you are getting what I was saying [apologies if you are]. When the PA is out, each individual sub will contain a certain amount of field rotation, resulting in some of the stars becoming streaks instead of points (and/or limiting the length of the sub). Certainly any slight variation in the postion angle of the camera from night to night can be sorted by the stacking software, but it generally can't turn stars that have streaked into single points. Neither can guiding software correct for this, unless you have a system that includes automated eyepiece-rotation [which, apart from being inordinately expensive, is, I understand, even more of a hassle than getting PA correct!].

 

 

To get an idea of how big star trailing effect could be there is a great great link here. Obviously the longer the exposure the worse it gets.

polar alignment error