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Evaluating the
Periodic Error
of the worm
Here a randomly selected
Paramount ME was intentionally moved
off the pole by an amount of 1.5 degrees in azimuth (shifted too far to the east)
to cause an inordinate amount of declination drift. The period of the worm of the Paramount ME is 2 and 1/2 minutes long (2.5
minutes = 150 seconds). Using an SBIG ST-8 imager
employing small 9 micron
pixels with 110 inches of focal length the following is an 8 minute long exposure
with a scale of
~1.0 arc seconds/pixel. Normally I would never image with this
unrealistic
scale on a commercial Schmidt Cassegrain at this focal length). However, for evaluating the periodic error this is a must. That is because the error is so small it would be lost in a larger pixel
especially when imaging with poor seeing (average).
The sine wave below is showing several periods
of the worm (3.2 periods). Note the smoothness and repeatability of the periodic error
on this randomly selected
Paramount ME. Great
pains are put into both cutting the gears and worms (done in-house) and then
accurately mounting them!
NOTE! ALL
Paramount MEs' are
run-in BEFORE shipping and the periodic error is measured in-house!
The Paramount ME is guaranteed to have 5 +-2 arcseconds or less of periodic error
BEFORE training the error. After the correction one can expect 1 arc
second of error or less when using
PrecisionPEC to train the error.
The somewhat large width of the sine wave
below is being caused by very poor average Colorado
seeing.
Sample trailed star
Click Image to EXPAND!
C-11 @ f/10 ST-8 - 9 micron pixels
(just under 1 arc second/pixel scale)
How to minimize the periodic error
in the Paramount
Announcing
PrecisionPEC
PrecisionPEC
Total error ~2.5 arc seconds before correction!
After uploading the PEC
table into the Paramount you can expect 1 arcsecond or less total error
after the correction. The easiest way to test this is simply log a star
a second time after enabling the correction.
Periodic error after
the correction is enabled
0.5 arcseconds up and down = 1
arcsecond total
The following image shows what can
be achieved by using Periodic Error Correction correctly.
PrecisionPEC
allows anyone with a CCD camera supported by
CCDSoft (excluding 8-bit
live video cameras) to easily record the periodic error, throw out the effects
of seeing, fit the data, and update the
Paramount ME's firmware
with the correction. This
requires minimal effort on the users part. The same 3.5 arc seconds of
error above has now been reduced to ~1.0 arc second.
16 minute Exposure
Click on image to expand
8 minutes with correction enabled
8 minutes without!
The above image is 16 minutes in length. 8 minutes without periodic
error correction a 15 arc second jog and another 8 minutes employing the
correction.
PrecisionPEC for the
Paramount ME ,
accept no substitute!
A quote from
Paramount ME customer
Michael Rice - New Mexico Skies, "Periodic Error is a
thing of the past.."
The following RAW data is the best
I have seen to date. After having the customer check and double check his mount
it turns out that he has less than 0.5 arcseconds of error without any
correction!
NO correction enabled!
0.4 arcseconds without correction!
Sample #2 - 1 arcsecond up and 1
arcsecond down
2 arcseconds
before correction!
Astounding
Here the amount of periodic error
BEFORE correction was slightly over 4 arcseconds. However, after logging the
data a second time with the correction enabled note the end result. The total
error is now on the order of 1 arcsecond!
0.5 arcseconds up and 0.5
arcseconds down
Data collected using correction
At this point the error is lost in
the noise!
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