Importance of polar alignment?

[ollypenrice]

Being observatory based I have good PA from long drift alignment. (I'm allergic to gadgets and softwar solutions to this simple problem.) I also autoguide.

But  I often read in the threads relating to beginners running unguided that good PA is of paramount importance. Is this really true? Running guided, a decent PA is of moderate importance but in reality it only really matters if you are running long subs. Sure, I like my 30 minute subs so I fuss over PA, but if you are running unguided over a couple of minutes how important is PA? Isn't periodic error pretty much the limiting factor?

Olly

 

 

[Jonk]

Image scale too I would have thought?

[Knight of Clear Skies]

I'm not sure really. One way to find out would be to make an animation from the subs like this:

(Comet Jacques passing the Garnet Star). It seems to stutter but it might not have been taken in a straight run, possibly I stopped to check the frames at a few points.

DSS also shows x and y offsets in pixels between subs, so looking at the figures there might shed some light on how the mount is performing. I tend to get sub-pixel drift between subs which does a lazy dither for me, as the camera isn't aligned along the RA & Dec axis. This can eventually mess up of the framing of tight targets though.

[ollypenrice]

17 minutes ago, Jonk said:

Image scale too I would have thought?

Yes, you're right, but image scale will be a constant across all tracking errors. I'm really wondering about the relative importance of PA and PE.

Olly

[barkis]

I used the Drift Alignment method too Olly. In my original domed Observatory which I built onto the end of my Garage, 
originally home to a  8" f6 home made Newt. later superseded by a 12" f6 also self made. These scopes were mounted on an  A frame, 
made fron 2.5" Angle Iron welded together. The Polar support part had two 2.5" self aligning bearings which were adjustable on the frame, to allow for 
tweaks to the Latitude. and Azimuth adjusting was achieved by a long 18mm threaded bar, which moved the A frame itself.
Once finally adjusted the whole frame was locked down to the concrete pillar on which is stood.
I followed guide stars through a Guidescope with a guide eyepiece with parallel crosshairs which formed a small box in the centre.
the crosshairs were illuminated by a small lilliput bulb painted red poking through the drawtube of the guidescope.
I adjusted the guide reticule so that moving the main scope kept a guide star within the  parallel  lines of the crosshairs.
Once achieved, centre the guide star, start the drive, and watch for any drift north or south, making adjustment to the PA as needed .
Of course, there are checks to be done a few degrees above and below the celestial equator, and east or west, to cover discrepancies in both Azimuth and Latitude.
Indeed a painstaking task.  My experience about this is going back  30 years, and Using an Olympus OM camera, and various types of  film Tri X  400    HP5 and others.
Never tried any hypering or anything like that. Some results were decent, but nothing sensational.   
A bit Heath Robinson, but it did work quite well.
However, I found it exciting, and always full of anticipation of great success. Got some decent Lunar pics. and Deeps Sky were basically a few Globulars M31, M42 and a few other.
Nothing to write home about, but I loved it. great fun.   Odd thing is, I have some great stuff today, a MN190, ED80, ZS66, Atik 314L+ Canon 1000D and much more,
however, I'm not filled with motivation for some reason, it's weird. My EQ6 Pro is pier mounted, in the OBS polar aligned, and all the other imaging requirement are there, 
But the inspiration just won't kick in.  Maybe I'm too much on the Golf Course, but that isn't exciting in winter. Astronomy ought to be though.
What were you talking about? ah yes, Polar Alignment, I've kind of drifted off a bit here. 

 

[gonzostar]

As a complete and utter noivce does this thread below help?

advanced vx & PEC - how does it work? by scorpious in aug 2015

I have reasonable polar alignment I do currently unguided subs of upto  2 minutes. I have found that Olly's advice a while back of going "east heavy" increased the number of light frames that where accepted by dss 

Cheers

Dean

 

[Tim]

You can probably get away with it, but when super tight PA is available in minutes, why would you? The more little things that are as good as they can be add up to an overall healthier approach I reckon.

Saying that, it has always bothered me at star parties that folk interested in getting space photos waste half the dark night setting stuff up rather than getting photons on the chip!

 

[cosmojaydee]

Rather than look at PA as essential, I would like to think its good practice. If you have someone who is new to astronomy looking for advice and would like to use a telescope sat on a German equatorial mount , is it not better sing of the same hymn sheet to coin a phrase, rather than offer conflicting advice?   

[ollypenrice]

1 hour ago, cosmojaydee said:

Rather than look at PA as essential, I would like to think its good practice. If you have someone who is new to astronomy looking for advice and would like to use a telescope sat on a German equatorial mount , is it not better sing of the same hymn sheet to coin a phrase, rather than offer conflicting advice?   

I'm not offering advice here, I'm asking for it. It is something of a mantra to say that very good PA is important for unguided imaging. What I'm wondering is whether or not this is really true. It's a bit like levelling mounts. Careful levelling is often recommended but is, in fact, not necessary at all.

Behind my question is Tim's point. Astrophotos are made with photons.

Olly

[cosmojaydee]

7 hours ago, ollypenrice said:

I'm not offering advice here, I'm asking for it. It is something of a mantra to say that very good PA is important for unguided imaging. What I'm wondering is whether or not this is really true. It's a bit like levelling mounts. Careful levelling is often recommended but is, in fact, not necessary at all.

Behind my question is Tim's point. Astrophotos are made with photons.

Olly

I understand its advice you were asking , but accurate polar alignment or any polar alignment would depend on so many different factors , I did a little research and came across this debate  http://www.cloudynights.com/topic/481144-polar-alignment-considerations/