[Fwd: Tracking Error Measurements for AP600]

RCK <rkuberek@...>

Reposting by request.

Bob Kuberek

RCK wrote:

Hi all,

I have done measurements of the tracking error of
the AP600 GTE mount using the ST7 camera. The
following table shows the sequence of adjustments,
in arcseconds, necessary to re-register the image
after each of ten 60 sec. exposures.

0.00 0.00
-4.70 0.00
-4.70 -1.57
0.00 -1.57
1 min. dark frame
6.27 -1.57
3.14 -1.57
-3.14 -1.57
-6.27 -3.14
1 min. dark frame
-3.14 -3.14
3.14 -3.14

As this shows, the RA errors range from -4.7 to 6.3
arcsec. over the 12 minute period, relative to the
initial (0,0) exposure. This RA error has a standard
deviation of 4.36 arcsec. and a total range of about
12.5 arcsec. (i.e., +/- 6.25 arcsec.).

The DEC drift, which I assume is due to the Polar
alignment error, is pretty steady. (Polar alignment
was not precise--interative N Polar Calibrate
procedure was used.)

The attached image, m1badx.jpg, shows the effect of the
tracking error on a sum of the 10 one minute expo-
sures, at an image scale of 1.56 arcsec. per pixel.
This image simulates the effect of the above tracking
errors on a single 10 minute, unguided exposure.

The second image, m1x.jpg. shows the result of re-regis-
tering the 10 exposures, then adding. This image simulates
the result of manually guiding a single 10 minute

The AP600 is tripod mounted and was balanced pretty
well in RA. The balance in DEC was not so good, even
though I had the scope pushed forward as far as
possible in the rings, since the ST7 is very heavy
with a flip mirror in front. The wind was calm.

Is this performance consistent with what other people
are experiencing with this mount? Also, I would greatly
appreciate any feedback or comments on my setup or
technique so I can improve my results.

Bob Kuberek


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