Phd2 polar alignment

[Andyk93]

Hi, I have just started guiding and figuring out how all this equipment works. What I would like to know is how close do I need to get polar alignment realistically when I setup every time and tear it down afterwards. I would like 2-5 minute subs. I have got it very close before but it did take over an hour and ate into my imaging time. See attached picture for how close I got, any help appreciated

[johnrt]

Well that is all going to depend on what focal length and pixel ratio you are imaging with, can you provide some details of your kit?

[Andyk93]

Sorry for not giving enough detail. I either use a SW 130pds or 200pds with qhy5 and 9x50 finderscope on an neq6. The focal length on the 9x50 is 180mm, the 130 is 650mm and 200 is 1000mm

[sloz1664]

If you are setting up and tearing down every time I would invest in a QHY polemaster. Providing you have access to Polaris. It save valuable imaging time, only takes 5 mins to accurately polar align and you would be more confident in obtaining subs in excess of 5 mins. I had the same issues when I didn't have my obsy and I wished I'd had the Polemater from the start. I still use mine now as I'm always bumping into my mount when sorting things out. One of the best "add-ons" I've purchased.

Steve

[cfpendock]

Just a couple of comments.  Your exposure times seem very short to 0.1 secs - you will be chasing the "seeing", so even at x giving 400 points you are only getting 40 seconds worth of history on view.  If you are looking for 5 minute subs it would be useful at least to see 5 minutes worth of guiding.  The y axis could be reduced to say 4  seconds of arc to show deviations more clearly - it is difficult to see what error you have although I would guess between one and two seconds of arc.

Personally I think 1.2 minutes of polar accuracy would be difficult to beat - but I am not sure that I would trust the PHD figure - other things such as mount backlash on the dec drive come into play.  In fact sometimes it is useful to have several arc minutes of error on the polar alignment just so you can get the dec driving only in one direction (doesn't apply to RA because you are ALWAYS driving in one direction, providing of course that you have adjusted your "out of balance" correctly).

Hope this helps.

Chris

[Andyk93]

Thanks everybody, given me some feedback as to what I can do, will definitely show you 5 minutes of guiding as soon as possible. what exposure time would you recommend? When I thought I had PA very good last time phd2 showed it was 10 arc minutes out. Guiding created more star trails than being unguided

[Ken82]

As long as your not imaging near the pole your absolutely fine with something in the region 1-5 minutes error! Your guiding looks reasonable but your exposure time is  to short I'd say even at your focal length . I'm sure many people waste time adjusting polar alignment when they could be imaging ! 

[JemC]

if you have the latest version of Sharpcap, there is a polar align feature in the tools,

i used it for the first time a few days ago and believe me it really is simple to use, i cannot compare it to anything else as not used anything else before,
this is what i ended up with Sharpcap saying my polar align error was on my first use,

 

 

[Andyk93]

1 hour ago, JemC said:

if you have the latest version of Sharpcap, there is a polar align feature in the tools,

i used it for the first time a few days ago and believe me it really is simple to use, i cannot compare it to anything else as not used anything else before,
this is what i ended up with Sharpcap saying my polar align error was on my first use,

 

 

That looks brilliant, any idea how accurate that is and does sharpcap just connect to my qhy5 through my finder scope? 

Thanks

[JemC]

16 minutes ago, Andyk93 said:

That looks brilliant, any idea how accurate that is and does sharpcap just connect to my qhy5 through my finder scope? 

Thanks

Yes it connects to qhy, i am using a qhy5l-iic with it, as for accuracy, its a lot better than i have ever had,  this image was taken after i polar aligned with it,

6x300sec images stacked

it really is easy to to use, i only ever polar aligned by eye with polar scope and was lucky if i could get 1 min without trailing, i really am just a novice so if i can use it anybody can,

when making the adjustments, (which it tells you which way to adjust the polar axis) just make sure you only make small adjustments otherwise you will be chasing it back and forth 
Also step 3 is the final step, you just need to get the number as low as you can and to something you are happy with(the program does not tell you when enough is enough) when you are happy with the lowest number you can get you just exit from it,

Regards

[Andyk93]

That is a brilliant picture. If I can get anything like that I will be extremely happy. I will be downloading that tomorrow and I'll have a go with it. Did you guide with phd2 as well? 

Thanks

[JemC]

3 minutes ago, Andyk93 said:

Did you guide with phd2 as well? 

i did  and it was the first time using that as well, overall i'm pretty pleased with the results so far,

just need some more clear skies so i can try some more,

[cfpendock]

16 hours ago, JemC said:

this is what i ended up with Sharpcap saying my polar align error was on my first use

I don't believe it is physically possible to achieve better than the 6 seconds polar alignment error shown, and I would be surprised if it was repeatable.  The mechanics of mount adjustment are simply not sufficiently precise.  But as Ken82 has pointed out above, between 1 and 5 minutes is fine.  I usually get between 1 and 2 minutes with my Tak EM200 which is a very good system.  I use this to image at 2800mm focal length, and my guide camera exposure time is never less than 5 seconds, giving around a half hour of guiding history on the graph.  At shorter focal lengths (around 500mm), I tend to use 10 second guide exposure times.  With your neq6 mount this should be no problem at all.  In fact, if the mount is in reasonable condition and with a reasonable PA (say less than 2 minutes) you shoulldn't need any guiding at all for two minute subs...

I would be interested to see your graph with longer guide exposures and a reduced y axis - from what you have posted so far it seems you could reduce by half at least.  Many people on this site (myself included) use 4 arc secs.

Chris