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My astronomy tutorials:
Drift align and auto guide calibration


  1. Mount polar drift align
  2. Auto guide calibration

I take no responsibility or liability for what are written here, you use the information on your own risk!

1, Mount polar drift align:

To have have good quality photos it's important that the mount is positioned correct against the polar star and in balance. This was earlier a part of my E6 mount project.

In this case it's a Windows system. ASCOM connect the different software with each other and I use EQMOD to control the mount. Here is some guide about EQMOD and PHD2 that control the mount:

This is partly connected to my test of the EQ6 mount after I converted it to belt drive.

Prepare the mount for drift align:

EQ6 Mount, Drift align and guide calibration

Before start to drift align the mount must point rough to the polar star. I can't see the polar star from my balcony so little bit more difficult. The latitude is easy, I simple measure the angle of the RA axis of the mount. 59 degree where I live. I noted later that the latitude scale pointed to 68 degrees, that's not where I live.

EQ6 Mount, Drift align and guide calibration

Checked with my spirit level, found it correct, I must have placed the scale on the mount i wrong angle when I did some work on it. Even better with a digital spirit level.

The azumutal angle I found from the shadow of the Sun. The Sun is in South at local solar time. It differs for different places +/- 30 minutes. Check in a table how much it differ from your local time at your place.

You can find the time from this page when Solar noon occur, NOAA. Click on the map where your place is and it calculate the time when solar noon is. Then a sunny day make a mark where you have the sun's shadow at your solar noon time. Don't look at the sun, look at the shadow from your mount ! At my place in January the solar noon time is 11:56.

Try to adjust your mount better than +/- 2 degree in both Latitude and Azumutal. Now the mount is ready for a drift align during a clear sky at night. This can be done during daytime.

CdC, Star chart:

EQ6 Mount, Drift align and guide calibration Star map Credit CdC.

From our balcony I can't see the polar star, still I have to do a polar align. I use the drift align method. The free auto guiding software PHD2 has one implemented. I control the EQ6 mount over the EQMOD driver through the star chart software CdC or Skychart.

I start to adjust the altitude, from the star map I choose a star close to the celestial equator (DEC = 0), in my case in Eastern direction. But the Western direction work as good too, depends in which direction you have a clear sight. I found a star 3 degrees above the celestial equator and ten degrees above the horizon. The star must be bright enough to get a good S/N ratio on the guide camera. In my case stars of magnitude 8 or brighter will do.

More to read about polar align at Wikipedia:


I use EQMOD to control my EQ6 mount.

EQ6 Mount, Drift align and guide calibration Mount controller Credit EQMOD.

In the EQMOD window I can see the coordinates the telescope is pointing to. The coordinates and time must be correct setup in EQMOD first.

PHD2, altitude adjustment:

EQ6 Mount, Drift align and guide calibration Drift Align, credit Open PHD2 Guiding.

After I have started PHD2 and initiate the mount and guide camera I open the drift align window, choose altitude adjustment. These software and drivers communicate over the standard ASCOM interface.

EQ6 Mount, Drift align and guide calibration

When drift align in work I can follow the DEC drift, the red line in my case. Look at the trend, is it upwards or downwards. When it's perfect the red line will be horizontal. In the window you can also see the polar alignment error, it's expressed in arc minutes / seconds or pixels. You must also do the azimuthal adjustment, that influence this altitude adjustment. Redo these two adjustments one or twice until it's stable.

I noticed how the guiding try to slow down the RA tracking. It's like the RA axis rotate too fast, strange. It's because a bug in the stepper motor driver of the SkyWatchers earlier EQ6 mounts. Use the EQMOD's RA drift compensation to cancel it out. When controlling the mount from the hand terminal this isn't a problem.

Drift Align, azimuth adjustment:

EQ6 Mount, Drift align and guide calibration

Switch over to azimuth adjustment, this image is before I move the telescope to the Meridian at the celestial equator. Note the notes I have written down in the window. It can be very confusing in which direction to do the adjustment, you need some support in the form of these notes.

EQ6 Mount, Drift align and guide calibration

In the end I got the error come down to one arc minute, much better than I have achieved before.

You are always reading the DEC trend, red line in my case. Both for altitude and azimuth adjustment !

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