Polar Alignment

Overview  Polar Align  Focal Length  Focussing  Find & Take  Processing  Color Imaging

Any astrophotography, be it CCD imaging or 35mm film, requires the telescope to be accurately polar aligned.  If you do not do this you will greatly increase the amount of work required to guide the telescope when taking an image and also run the risk of seeing star trails in all but the shortest of exposures.  The simplest and most accurate method of polar alignment is known as the drift method.  The best description of the drift method I have seen was written by Philip Perkins and can be accessed here.   The drift method can be quite time consuming.  However, by doing some simple things before starting drift alignment you can greatly reduce the time it takes.

  1. Adjust the azimuth of the OTA so that it is pointing roughly towards the pole star and ensure that your equatorial wedge is set to your current latitude using the scale on the wedge.

  2. Make sure your telescope is level.  Check the base of the equatorial wedge with a sprit level and place shims under the tripod legs until it is level in all directions.

  3. Do a reasonably accurate polar alignment prior to starting drift alignment.  I developed the following method for use with the LX10:

    Switch on the telescope RA motor

    Look up the current sidereal time in a planetarium program

    Calibrate the RA scale on the telescope. To do this, find the point on the RA scale that represents the current sidereal time. Now turn the scale so that this point is at a 6 o'clock position as you look directly face on to the RA setting circle.  The RA circle is now calibrated.

    Set and lock the RA of the OTA to 02:32 using the RA setting circle

    Set and lock the DEC of the OTA to 89.2 using the DEC setting circle.  This assumes that your DEC setting circle is correctly calibrated.  You can read a description of how to do this here.

    Adjust the azimuth and latitude of the OTA (do not adjust the RA and DEC setting) until Polaris is centered in the viewfinder and again until it is centered in the telescope eyepiece.

    For the LX200 and RCX400, some of the above steps are automated by the handcontroller.  If you choose Polar Alignment from the menu you will be asked to set the RA to the 6 o'clock position described above and the DEC to 90 degrees.  When you have done this the LX200 will automatically slew to the RA and DEC of Polaris.  You can then adjust the azimuth and latitude of the the OTA until Polaris is centered in the eyepiece.

  4. Perform the drift alignment process.

I have found that when you have done steps 1-4 once,  you only need to repeat these steps for the azimuth axis the next time you need to do a precise polar alignment.   This is only true providing you level the telescope accurately, have not changed the latitude setting on the equatorial wedge since the previous alignment, or moved the location of the telescope to somewhere with a significantly different geographic latitude.

If you have your telescope permanently mounted on JMI wheely bars and just move it in and out of your garage then you only need to perform drift alignment once.  The first time you move it to its normal imaging position you need to perform drift alignment as described above.  Once that is complete draw a circle around each of the wheely bar foot pads.  The next time you move your telescope to its imaging position locate the wheely bar pads in the circles you drew last time and make sure the telescope is level like it was when you did the drift alignment.  This will give you an accurate enough polar alignment for CCD imaging.

The Takahashi EM-200 mount has an integrated polar alignment scope that makes polar alignment very straightforward.  It can be done in just a couple of minutes and is accurate enough to enable CCD imaging without aligning using the drift method.