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Drift Model
The Drift model is an alternate way to measure an object’s path through the sky and then use it to compensate for drift for
unguided imaging. It does not require any external planetarium software - it is a self-contained keypad routine. This model
allows the user to build a tracking path for any object as it moves across the sky for a number of hours from East to West.
The model measures the drift of stars along the constant declination of the object and applies the proper tracking rate in
both RA and Dec axes to keep the object centered and not drifting for typical exposures of between 5 to 20 minutes.
The key is to measure the drift very accurately at several points along the path, starting with the object and moving West
at several intervals. One simply does a GoTo slew to the object to be imaged, centers the object and takes a quick image
to display some stars. You then pick any star, draw a small focus box around it (with crosshairs enabled) and begin a fast
continuous download of the image. Magnify the image on the screen to perhaps 800x and center the star on the crosshair
using the N-S-E-W buttons at the appropriate centering rate (.5x or .25x is recommended).
Up to 8 data points on each side of the meridian can be stored at the object’s declination. New object paths at different
declinations can be measured as desired and simply added to the existing data. As long as the mount is not disturbed or
moved, the data will be valid for future imaging sessions.
The upper right corner of window 5221 displays the number of data points that have been added for any particular Dec
line. A new declination data line is created when a star is entered 10 degrees from the original. Dec lines are created at 10
degree intervals from -90 to +90 degrees. Each Dec line is a corridor that includes any star that is within 5 degrees of the
first one. Up to 8 stars can be measured and entered as data points on any one of 16 declination lines in the model. The
first declination line will have numbers from 1 to 8. The second Dec line will have numbers from 11 to 18, the third will have
numbers from 21 to 28 and so on. As an example, a number 64 means that the 7th Dec line has 4 data points in it, and the
user can add 4 more before that line is full
The east and west models are independent. All mapped points are remembered through power cycles, available for
correction in subsequent sessions, until you create a new model.
1. Go to Drift Model window.
(Main Menu > 3=Tools > 2=Modeling).
2. Select 3=New Model if you have not created a model previously.
Window 5221 will appear. The upper right will
read “ D Pts:000” since you do not have any points in your model when you start.
3. Set your button rate (toggle 6), center a star near the object you wish to image and press ENT.
Window 5222
will display.
4. Allow some time to pass in order for drift to occur.
The keypad window suggests 5 minutes, but the time can be
less - at least 10 seconds.
5. Check your crosshair and recenter the star with your keypad buttons.
If your camera can be put on video mode,
this may facilitate quick centering.
6. Press ENT.
This will register the drift measurement data at that point. Window 5223 will appear.
7. Press < or > to command the mount to move E or W in RA by 7.5 degrees (1/2 hour).
Press the West button (>
button) to move 1/2 hour, or press it again to move 1 hour. Each press of the button moves the mount by an additional
1/2 hour. It is recommended to move the mount by 1/2 hour if you are below about 45 degrees altitude, where the drift
changes quickly. Above that altitude the drift is more regular and you can begin each point at 1 hour intervals. Generally
it takes only 3 points above 45 degrees altitude and perhaps 3 - 4 points for locations between 0 and 45 degrees.
8. Press ENT.
The mount will slew in the commanded direction.