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APPENDIX A: DECLINATION AXIS BACKLASH TESTS
PulseGuide™
PulseGuide™
is a free software program, developed by Ray Gralak, to provide keypad-like functionality using a computer.
It offers the additional feature of a Dec. axis backlash test. You can download it through Ray Gralak’s website.
Once you have started the
PulseGuide™
application and have connected to
the mount, go to the “PEM/other” tab and click the “Backlash Tests” button to
bring up three tests suggested by Roland Christen to test the performance of
your declination axis. Roland posted some tests that you can run on your AP
mount to see if it has a potential problem with Dec movement.
IMPORTANT: Before running tests 1 and 2 set the mount’s backlash to 0.
Also while performing the tests do not try to auto-guide.
Dec Backlash Test 1
Before starting Test 1 set up your
camera control program (e.g.
MaxImDL™
,
CCDOps™
, etc.) to
do a 100 second exposure (but do
not autoguide). You can also set up
an auto-dark exposure, but make
sure that you start the test when the
camera control software is exposing
the light image.
Once you start the exposure press the Start Test 1 button. With the default settings
(recommended) the entire procedure will take about 90 seconds.
Test 1 will move the scope in this manner: East - pause - West - pause - East to center -
North - pause - South - pause - North to center.
The stars in the resulting exposure should look something like the image to the right. The
scale might be different but you should see what looks like many plus signs in the image.
If you take the image near Dec=0 the height and width will be about the same. Although not
shown in this particular image the East and West points will be slightly brighter than the North/South points. This will make
it easy for Roland to establish the orientation of the camera.
Dec Backlash Test 2
You will run Test 2 three times, once for each of the
guide rates. Before starting this test set up your
camera control program (e.g.
MaxImDL™
,
CCDOps™
,
etc.) to do a 25 second exposure but do not try to
autoguide. You can also set up an auto-dark exposure,
but make sure that you start the test when the camera
control software is exposing the light image.
Start by setting the Guide Rate to 1x. Once you start the exposure press the Start Test 2 button.
With the default setting (recommended) the entire procedure will take about 16 seconds.
Although the scale might be different, the stars in the resulting exposure should look something
like the image shown.
For reference the actual movement in Test 2 is: North+West - South+West - West only (the pause
setting) - North+West.
Now you will need to repeat the tests at 0.50x and 0.25x. The star patterns will look similar
but smaller because the movement rate is slower. Here are two examples taken with a
Traveler:
0.5x
0.25x
1.0x