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 very small so the field of view is much smaller than when you use an
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, and since 'that tree' is no more there I can see Polaris.
Here is how I Polar Aligned my LX200 10" f/10 Classic which is permanently mounted on my pier and wedge
Guideline: Polar Alignment (on Polaris) by using a webcam
- I started - more or less - conform the Meade Manual and:
- Made sure the North/South switch was in the NORTH position (I live in the Northern Hemisphere)
- Made sure my Latitude and Longitude were correctly entered
- Made sure the time [recommended setting: 24 hour mode] was also correctly entered with the correct offset to GMT
- Precisely lined up the finder with the main scope by aiming at a bright star
- Looked up the DEC of that star and calibrated the DEC setting circle
- Used the Keypad to set the HA at 00 and the DEC at 90
- The scope slewed to where it assumed Polaris
- Of course I was not on Polaris so I rotated the wedge and also adjusted the angle of the tilt plate to bring Polaris exactly at the centre of the crosshairs of the finder. I adjusted even more precisely by looking through the eye piece and centring Polaris right in the centre. Synced on Polaris.
- GoTo Procyon: I used the Keypad to exactly centre Procyon in the centre of the eye piece. Synced on Procyon.
- GoTo Polaris: still off. I rotated the wedge and adjusted the angle of the tilt plate to bring Polaris HALFWAY to where I wanted it to be.
- GoTo Procyon: again I used the Keypad to exactly centre Procyon in the centre of the eye piece. Synced on Procyon.
- GoTo Polaris: still a bit off, but improving. Once more I rotated the wedge and adjusted the angle of the tilt plate to bring Polaris HALFWAY to where I wanted it to be.
- GoTo Procyon: once more I used the Keypad to exactly centre Procyon in the centre of the eye piece. Synced on Procyon.
Next I mounted my webcam and centred even more precise by looking at the K3CCDTools preview screen.
- GoTo Polaris: yes, it was on the K3CCDTools preview screen, but not in the centre.
I applied a final minute rotation of the wedge - I had attached a spanner to the wedge to be able to make small and controlled movements - and also carefully fine tuned the angle of the tilt plate to bring Polaris almost to where I wanted it to be. Synced on Polaris.
- GoTo Procyon: BINGO! Procyon is almost in the centre of my screen, meaning that even with my webcam mounted I can GoTo where I want to go.
- DONE !
- And with my permanent setup I only have to do this once: on my next session I only have to 'sync' on a known bright star and I am in business.
However: what to do when you cannot see Polaris because of a blocked view? I use Drift Alignment!
Note: the following procedure is based on my own experience and as a webcam imager I of course used a webcam.
But the same procedure can be used visually too, be it with less accuracy.
Guideline: Drift Alignment by using a webcam
- Set up your scope and rotate the wedge North/South as good as you can.
- Now aim at a rather bright star in the South, best is to select one close to the celestial equator.
- Centre this star in your eye piece.
- Mount your webcam and use the Keypad to move the star to the centre of your screen.
- Use rather short exposure time, so that the screen refreshes frequently.
- Lookup the DEC of this star on a star map and calibrate your DEC setting circle.
- Next use the East/West buttons on your Keypad to move the star East/West over your screen.
Rotate your camera until the star goes in a straight horizontal line over your screen.
You can fine tune this by using the Reticle function of K3CCDTools, which puts nice crosshairs on your screen.
The result of this step is that your webcam is now perfectly East/West oriented.
- Move the star to the centre of your screen and watch closely.
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.
This East/West drifting is called the Periodic Error (PE) of your mount, which is caused by imperfections of the mechanical components of the mount, most likely the RA worm shaft and gear and the related bearings. These tracking problems are outside the scope of this tutorial, but you should read the section in the Meade Manual about PEC training.
We continue with the Drift Alignment and first address the North/South orientation [Azimuth] of the wedge:
- Look closely at your screen at the star: does it move up or down?
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: now you can see what is happening.
Even better: use the K3CCDTools Drift Explorer to assist you with a graph.
If the star drifts upwards or downwards this means that you must ROTATE the wedge.
You should do this in small steps and continue to watch the K3CCDTools preview screen and the Drift Explorer graph.
Continue to rotate the wedge till the up/down drift has been eliminated.
Now the angle of the wedge's tilt plate [Altitude] must be adjusted:
- Aim at a bright star as far East or West as you possiby can, preferrably on or close to the celestial equator (DEC 0).
- Also this star should not drift up/down on your screen.
If it does: adjust the angle of the tilt plate till the drift has been eliminated.
- You might have to execute the Azimuth and Altitude adjustment procedure once more to fine tune your polar alignment.
- DONE !
HINT: A more precise approach.
The Drift Explorer of K3CCDTools is a nice help with polar alignment, but sometimes the changes are hard to see/interpret,
even when at 'max'.
The other night I had Altair 'on screen' with my LX200 in prime focus and the Drift Explorer was running.
Then it dawned to me, that when I would fool K3CCDTools and specify a smaller focal length than the 2500mm the readings from the Drift Explorer would be much more aggressive. Quite obvious of course, but I simply never thought about this ...
So I tried with 700m and yes: the peaks/vallies were very huge now, so fine tuning is much easier as I can better see what I
am doing ....
In the K3CCDTools forum Peter Katreniak revealed a hidden treasure:
"The graph in the Drift Explorer is more "smart" than it would seem: it has a very useful ZOOM function for the fine polar alignment.
To Zoom a graph area, hold the left mouse button and drag mouse toward down/right.
You'll see a rectangle around the selected area.
Release the left mouse button to perform Zoom.
You can continue zooming again and again.
To RESTORE (or UNDO) the zoom, drag a rectangle in the opposite direction (up/left).
Using the above trick you can achieve any required zoom level.
You can also use right mouse button to move the graph area to a required position."
Other recommended Polar Alignment sites:
LX200 Polar Alignment Procedure - Iterative Method by Philip Perkins
LX200 Polar Alignment Procedure - Drift Method
by Philip Perkins
What is drift alignment? by Bruce