polar alignment and autoguider

[caj1311 (Cindi)]

Having just ordered my autoguider, and having just spent an hour out on the paddock trying to do my polar alignment, I am interested to know whether using an autoguider lets you be a bit less precise with your polar alignment (please let the answer be yes!! )

[Somnium (Aidan)]

Originally Posted by caj1311

Having just ordered my autoguider, and having just spent an hour out on the paddock trying to do my polar alignment, I am interested to know whether using an autoguider lets you be a bit less precise with your polar alignment (please let the answer be yes!! )

haha sort of ... but the fewer corrections your mount needs to make the better the images you will get. it also depends on what focal length you are imaging and how long you are imaging.

[RobF (Rob)]

You really want to be quite close Cindi. Depending on your focal length, the worst case is getting frame rotation during a long sub in the corners of your subs even while guiding.

I'd flip your question around, and say rejoice - with an autoguider, its now easier than ever to more quickly get even better than normal PA

[tileys]

Haha,

I had hoped the same when I got my QHY5 (using an NEQ6). I think you still need to be fairly close but it certainly helps. I've found that with the guide camera I can still drift a bit if my alignment is out (PHD graph shows the deviation well).

Maybe with some more aggressive settings on the ST4 adjustments I could do better but my imaging definitely improved with an auto guider.

[The_bluester (Paul)]

For any real length of sub you will still need a good polar alignment, but as Rob wrote, once you have an autoguider you can use software to speed up the alignment process.

I was actually fiddling with this recently, I was never going to get an image on the night I was playing around and I wanted to see if a planetary camera (An old Celestron one) was sensitive enough to guide with (Fat chance) so I started playing around with the frame and focus mode in Backyard EOS on a star near the horizon, if you align the camera consistantly you can see which direction a star is drifting in Dec and use that to help tweak the alignment of the mount. Basically the same thing as people do in the likes of PHD but more manual.

[barx1963 (Malcolm)]

Paul
BY EOS has a function that puts a reticle on your screen that you can tweak so it works exactly the same as the reticle in an eyepiece. I tried it and it was much easier to use than an eyepiece. The only issue was that as the feed is direct from liveview, you can only use fairly brights stars. Unless you set up a loop of longer exposures.
I also tried the PA alignment routine in PHD2 and it worked really well once you worked out which way to move the mount.

Cheers

Malcolm

[The_bluester (Paul)]

One advantage to what I was doing and I will probably still do it when I have a guide camera is that I was using my main scope (So in my case long focal length) for the alignment, that will mean any error will show up a lot more noticeably. Once I get a guide cam (Budget, always budget!) I will probably use PHD and the guide cam in the main scope when setting up as it should make the error much more pronounced, then move the guider to the guidescope.

[caj1311 (Cindi)]

Thanks everyone - sounds like I am still just going to have to practice the drift alignment...

Hopefully the autoguider will make it a bit easier, and also maybe forcing me to get technological and attach it all to the laptop will actually help too...

Trying to find a way around crawling all over the ground and standing on a little step ladder as I align - tell me it is possible...

[Somnium (Aidan)]

you should be able to get a good drift alignment in 10 mins with practice. the best thing to do is get a spot that you can repeatedly go out to and get a really good PA, then mark the ground where the tripod legs are with tape. makes life a whole lot easier, then you do't really need to PA each night

[Howard (Howard)]

Hi Cindi,

You'll always be learning something new with astronomy

If you are jumping into autoguiding in the near future, then there is actually a way to do drift alignment using your autoguider. The following url has a good outline of this method (along with a stack of other polar alignment methods).

http://njstargazer.org/PolarAlignment.asp

I got shown it by an Astrophotographer who did not own any eyepieces! Just had cameras! Quite a neat method. And if you are going to autoguide anyway, then use it to both align and then guide (saves some setup time), and in the learning process you will learn heaps more about your autoguider and how it all works.

Cheers
Howie

[The_bluester (Paul)]

Time to throw in a question for those more experienced at it than me (Which is not hard)

I see many people setting up mounts, then doing one, two or three star alignments and then going to drift alignment with the likes of PHD, at the end of which if they do not switch off and realign they will end up with less than great pointing accuracy as the mount has been moved since the star alignment was done. Wouldn't it be better to simply power up the mount, switch on the RA drive to track and then aim at any suitable star near the horizon and then near the zenith to do the drift alignment to sort out the PA, then switch off, power up again and carry out star alignment to enable goto? It has always struck me as a step in the process (Star alignment before drift alignment) which does not really need to be there as the second step means the first has to be redone.

[kens (Ken)]

You want your PA to be close but not perfect. A little bit of slow drift in dec lets you set the autoguider to only correct in one direction. This helps avoid backlash issues.
I find doing PA with PHD so much easier than any other way.

Paul - what you say makes perfect sense. I don't need an accurate goto to find a star to drift align on.

[Howard (Howard)]

Yup. You most definitely must do a star alignment after doing any sort of polar alignment.

As you said, by doing the PA you have then 'broken' the original star alignment as you have moved the mount around. But you don't have to power off the mount to do that second alignment.

Is it a 'waste of time' to do the star alignment before doing the polar alignment? IMHO ... yes, it is a waste of time.

The astrophotographer I mentioned in my previous post (who showed me PA using an autoguider), did the autoguider drift alignment first, then did star alignment after that. I've heard that Paramount (mount manufacturer) did/still-do (?) recommend adjusting ALT and AZ bolts on the first alignment star centering it in the finder, and then fine tune using HC buttons in the main OTA. This effectively does a quick PA right up front as the 'map' in the mounts 'brain' thinks the start up position was perfect. So long as the OTA was correct in DEC (OTA parallel to mounts axis) and correct in RA (head and counterweight bar vertical) then that powerup 'map' will closely match the stars actual RA and DEC, but be out far more in PA. So slewing to the first alignment star and fixing the mounts AZ and ALT on slewing to that first star, corrects PA heaps right up front.

Having said that, I think any continuance of the debate on this (which might come) should be in a separate thread rather than in Cindi's / this thread

cheers
Howie

[caj1311 (Cindi)]

Originally Posted by Howard

Hi Cindi,

You'll always be learning something new with astronomy

If you are jumping into autoguiding in the near future, then there is actually a way to do drift alignment using your autoguider. The following url has a good outline of this method (along with a stack of other polar alignment methods).

http://njstargazer.org/PolarAlignment.asp

I got shown it by an Astrophotographer who did not own any eyepieces! Just had cameras! Quite a neat method. And if you are going to autoguide anyway, then use it to both align and then guide (saves some setup time), and in the learning process you will learn heaps more about your autoguider and how it all works.

Cheers
Howie

Thanks for that - I might give it a go

[The_bluester (Paul)]

Originally Posted by Howard

Having said that, I think any continuance of the debate on this (which might come) should be in a separate thread rather than in Cindi's / this thread

cheers
Howie

I am happy enough to have had it confirmed that what I thought was a largely redundant step is in fact just that (Which might be handy for the OP too) It is not going to do any harm so long as the star alignment is redone after polar alignment is refined but not really required. If others want to discuss it to and fro they can start a thread, I am happy as is.

[RobF (Rob)]

If you know your mount and set up location well, there's nothing to stop you slewing to known star, tweaking your AZ adjustment bolt a smidge to get the star close, then doing drift, then a proper star alignment.

The last step is rarely needed by astrophotographers nowdays anyway - just check and use platesolving to fine tune the final pointing.