Please note that the Polar Alignment Tutorial for my LX200 is here

If your scope is poorly polar aligned, the celestial object slowly but very surely disappears out of your field of view.
This hurts especially when using a CCD camera: the chip is only 4.6x3.97 mm (or maybe even smaller) so the field of view is much smaller than when you use an eye piece.

For CCD imaging it is absolutely vital that you have an (almost) perfect polar alignment, especially when imaging deep sky objects which require longer exposure times. Usually Polaris is used for polar alignment, but what to do when you cannot see Polaris because of a blocked view?

I use Drift Alignment!

In K3CCDTools there is a nice function to determine the Drift and I highly recommend you to use THAT functionality.
However, being an old guy I tend to stick to my own proven procedure......

I am facing the following constraints:

  1. I have an inexpensive telescope with no fine tuning for polar alignment: mine has clamps and a coarse scale with degrees only.
  2. My mount is not a tripod, but a pillar.
  3. Because of 1 and 2 I cannot use the polar alignment functions of Astrosnap.
  4. I have a permanent set up in my observatory, but I cannot see Polaris, and I have only a limited view both east and west. So I must use the drift method to Polar align my telescope.
    Note: spring 2005 this situation has changed: the neighbours felled a huge tree and now I can see Polaris. As I am used to the Drift Alignment I will stick to this procedure; also I think this is the most accurate method.
  5. I live on the Northern Hemisphere, hence those living on the Southern Hemisphere will have to read South where I write North etc.
  6. I have a Newtonian telescope, and the adjustments and findings are intended for my Newtonian. Users of an SCT telescope with a 90° diagonal mirror/prism must reverse the adjustments.

My mount has clamps only ...

Guideline: Polar alignment of a Newtonian telescope by using the webcam

  1. Set up your scope and point the polar axis as good as you can at (where you assume) Polaris.
  2. Aim at a rather bright star in the South, best is to select one close to the celestial equator.
  3. Centre this star in your eye piece.
  4. Mount your camera and try to get the star in the centre of your screen.
  5. Use rather short exposure time, so that the screen refreshes frequently.
  6. Turn your RA motor OFF.
  7. Because all stars rise in the East and set in the West, this star should drift from right to left (East to West) on your screen in a straight horizontal line along the longest side (= the width = in landscape) of your frame.
    If the star drifts from left to right, then maybe your camera is mounted upside down …..
    Rotate your camera until you get this straight horizontal line going from right to left (= East to West).
    You can fine tune this by using the Reticle function of K3CCDTools, which puts nice crosshairs on your screen.
    Please note that the top of your screen is South and the bottom is North. Now your camera has the correct and reproducible angle on your scope.
    For my own convenience I have made (white) marks on my cameras and scope, so that I do not have to readjust every time I remount the camera.
  8. Turn your RA motor ON again and centre the star on your screen.
  9. The star should not drift to the left or the right of your screen, but stay right in the middle.
    If the star drifts left or right in on your screen it does not have to do with poor East/West alignment: it is due to poor tracking.
    Either your tracking is too slow (star moving West (to the left on your screen)) or too fast (star moving East (to the right on your screen)).
    This might have to do with your motor speed or incorrect gears.
    Or you suffer from Periodic Error (PE). This is caused by the mechanical components of your telescope, most likely the worm shaft and the worm gear. These tracking problems are outside the scope of this particular guideline, but here you can see what I did to improve the tracking of my TAL-2M telescope.
    Suggestion: search the Internet on ‘Periodic Error’, maybe in combination with your scope model.
  10. The only axis you can adjust with a star located due South, is the East/West axis.
    To help you in determining the drift direction it is highly recommended to use the Reticle function of K3CCDTools, which puts nice crosshairs and circles on your screen.

    If the star drifts to the North (downwards on the screen), then this means that your polar axis is pointing too far West: the scope starts its down curve before the star does.
    Adjustment: move the polar axis of the scope to the East.

    Hint: to do this you need to rotate the equatorial head on your mount.
    I used K3CCDTools - Drift option - to see how I was doing. As I have only crude controls to adjust in azimuth I use a long square tube of aluminium which I poke in the equatorial head and then very gently I apply minimal pressure at the other end of that tube so that I can make very small adjustments in azimuth. Usually I keep looking at the screen so that I do not overshoot: small steps are the best IMHO.


    On the other hand if it drifts South (upwards on the screen) then your polar axis is too far East: the star starts its down curve before the scope does.
    Adjustment: move the polar axis of the scope to the West.

    Now it becomes really difficult for me, because from my observatory I have only a limited view both East and West. I will interpret ‘due East’ as ‘as far East as possible’ etc. and hope for the best of it.

    It is time for the second step, that is check a star either due East or due West.
    If you do the aligning using a star on the West horizon then the following applies:
    If the star drifts North (to the bottom of your screen), that means that the polar axis is too low. Adjustment: elevate the polar axis.
    If the star drifts South (to the top of your screen), the polar axis is too high. Adjustment: lower the polar axis.

    If you use a star on the East horizon, then:
    If the star drifts North (to the bottom of the screen), that means that your polar axis is too high. Adjustment: lower the polar axis.
    If the star drifts South (to the top of the screen), the polar axis is too low. Adjustment: elevate the polar axis.

When you have done all this, the star should remain right in the centre, also after a rather long time.
Verify this by using longer exposure times now, say 30 seconds and record them (during 15 minutes or so) as an AVI. When you play this AVI afterwards you can see if your polar alignment needs additional fine tuning. Further refinement can be achieved by repeating the above scenario with Barlow lenses.

IMPROVED PRECISION METHOD
I just found a way to use your long exposure webcam for refined and easy Polar Alignment.
All what is said above is still valid, but now I use the long exposure capabilities of the webcam and Preview mode of K3CCDTools to get exact Polar Alignment.
Here is - in short steps - what I do:

1. Make sure the cam is PERFECT East-West aligned (as explained above).
2. Make sure you are in PERFECT focus (use a bright star to focus on).
3. Point the scope due South, rather low in the sky (try to avoid turbulence however).
4. K3CCDTools in Preview mode, long exposure: say 25 secs. No need to aim at a bright star: you will catch all the stars you need!.
5. Watch the shift between frames and adjust the direction of the polar axis (as explained above).
6. Same procedure for East or West and adjust the elevation (Latitude or DEC) of the polar axis (as explained above).
7. Result: no more shift and PERFECT polar alignment has been achieved. Proven during a 75 minutes unguided imaging session:

July 15, 2003. I imaged M27: 150 frames of 30 secs and summed in K3CCDTools with the 'if lighter' option.
The vertical shift is really minimal: you see the total shift of 75 minutes!
Compare with the (few) hot pixels on the image.

The Periodic Error is visible too. In fact my PE is smaller, but I am still trying to find the perfect motor speed (my motor controller has a 'variable speed' option.

July 15, 2003. I imaged M27: 150 frames of 30 secs and summed in K3CCDTools [with the if lighter option].
The vertical shift is really minimal: you see the total shift of 75 minutes!
Compare with the (few) hot pixels on the image.

The Periodic Error is visible too. In fact my PE is smaller, but I am still trying to find the perfect motor speed: the APM motor corrector for my TAL-2M telescope has a variable speed option.

July 21, 2005: also see my Tutorials about the Periodic Error and Autoguiding.

Some links for further study and information:
QCUIAG member Tom Goode's explanatory image
What is drift alignment? by Bruce Johnston
CCD Polar alignment by J. Hall