Drift alignment - just checking I've done it right

[Carole]

Right, well after reading up a number of articles on this I've done my first drift alignment, and in the end it went so well I can't believe I've done it properly.

I used K3CCCD tools to open up a screen with a reticle and slewed my controls right and left turning the camera until the star was moving along the line horizontally.  Then switched off the tracking and watched for a while the star (Altair) drift and then adjusted the latitude controls.  Got it running pretty much along the line.

Did the same for I think it was Arcturus (no Eastern horizon), and that seemed to go vertically almost immediately. 

I probably should have chosen lower stars, but for my first "go" at this, in principal do you think I have got the right idea, and should I do it again with stars closed to the celestrial equator.

Also how long should I monitor the star?  I did it for about 5 minutes each.

Carole

[Mac]

Then switched off the tracking

you need to keep the tracking on. and then watch the stars,
depending on how far out the alignment is you should see some drift after 5 mins.

do it due south to start with. and make the adjustments as necessary,
The star will drift in both directions!!!
you are only adjusting for one of them!!!

once you are happy the star is not drifiting in the one direction you are working on.
then select a star in either the east or west, depending on which horizon is more favarable,
then select the star and drift align again.
adjusting for the direction you are working on.

this might help you.
http://www.andysshotglass.com/DriftAlignment.html

Mac

[Carole]

Hi Mac,

Thanks, that was one of the references I used.

you need to keep the tracking on. and then watch the stars,

However this is a quote from one of the sites I used which was why I turned off the tracking:

Switch on your telescope so you can use the direction drives in RA and DEC, but do not engage any automatic tracking.

I did turn the motors back on but without tracking. 

Carole

[Mac]

you need the telescope to track,

have a look at this simulator
http://www.petesastrophotography.com/

and click on the drift simulator.

[Carole]

Well I must admit I would have thought it was logical to have the tracking on, so that website was incorrect then.

I'll have to have another go then.

Thanks
Carole

[Carole]

Just looked on another website and got this:

The drift alignment method involves tracking the telescope on TWO different stars in specific locations of the sky, and watching these stars in an illuminated reticle eyepiece. By monitoring their movement, or drift, relative to the illuminated reticle, one can determine how to adjust the mounting in altitude and azimuth to obtain a precise polar alignment.

Conflicting information so thanks Mac, good job I checked.  

Carole

[Mac]

i'll have a look, but on of my many bookmarked websites, showed you why you need to drift align on two stars, one south, the other either east or west.



basically, if you align the eyepiece up so the stars run along it, then with the scope facing DUE SOUTH, center a star and observe the star.

Ignore any east / west movement, watch which way the star moves, If it moves down you are pointing to far north so you will need to move the star in the eyepiece up i.e. back to where you started.

Once you have aligned the n/s and the star no longer drifts up or down (with respect to the eyepiece line) move the scope to the East or west and do the same
place a star along the line. (assuming you are looking EAST)

the star will now move either up or down, with respect to the line, just remember UPRIGHT.

If the star moves UP, you need to move it RIGHT in the eyepiece.
As you move it right it will move out of view, just re position the star back on the line, and re-observe the drift.

If you use the simulator, turn on the pole star bit, and move it so its centered (i.e. polar aligned), then selecting either the n/s or e/w.
move the pole star to the furthest n/s or e/w position and see which ways the stars will drift, it might make it easier to understand what you are looking at.

Mac.

ps. wont be over this week as im stuck at barking on days, due to that fire.

[MarkS]

I've never done drift alignment but I would imagine that periodic error in the mount drive will also cause it's own cycle of apparent drift. So you might want to observe the drift over a period of a complete turn of the worm.

[Carole]

Looks like I need to do it all again.  Probably will be easier second time round even with modifications to what I did last time, as less new things to get my head around.

Mac I will be temping 3 days a week in the next two weeks, so can you make it a Monday or Tuesday. 

complete turn of the worm

Mark, what does that mean?

Carole

[Mike]

I've never done drift alignment but I would imagine that periodic error in the mount drive will also cause it's own cycle of apparent drift. So you might want to observe the drift over a period of a complete turn of the worm.

Or do a PEC routine before the drift alignment.

[Carole]

PEC routine before the drift alignment.

One step at a time I think Mike.

Carole

[Ian]

Yup, its iterative. Pec is more accurate with a good polar alignment, and that is more accurate with a good pec routine. Start by polar aligning, and as mark says use a reasonable duration to minimise the periodic error.

Also, bear in mind that how accurate you pec and polar alignment needs to be is related to the focal lenth and pixel size of the sensor. If you can't see any evidence of drift in your exposures, the pec and pa are good enough.

[RobertM]

Hi Carole,

PEC won't affect polar alignment since you're looking at north/south (Declination) movement with the drift method.  PE will only affect East/West motion (Right Ascension)and will guide out so I shouldn't be worried about that.  I'm not sure anyone in the society uses Periodic Error Correction and I would say that if you're autoguiding there is no point.

Robert

[Carole]

Thats a relief Robert, Ian's post rather overwhelmed me. 

Carole

[Rocket Pooch]

Hi Carol,

It is easy and as Robert said there is no issue with the PE of the mount when you have done it.

I have used K3CCD, at this time in the year I would use a star due south at 45deg to north, this has the most movement from polaris.

Ensure your star moved ion the X & Y correctly, you can do this by stopping the mount or using the hand controller.

The follow these instructions.

http://www.iceinspace.com.au/63-544-0-0-1-0.html

Chris