TPoint:
Making Polar Alignment Adjustments
Paramount
ME Altitude/Azimuth Adjustment Knobs
The
Elevation and Azimuth adjusting knobs on the Paramount
ME allow for very precise
polar adjustments to be made easily and accurately. When you loosen one axis to make the
necessary adjustment the other axis will remained fixed. For example, when the Paramount
ME is completely free to be moved in elevation the only change you will see is
in the up and down direction. The same is true for azimuth East - West movement
only. When the mount
is moved in azimuth you see movement in only the left and right or East and West direction. Perform the adjustments one axis
at a time. When the star doesn't jump all over the place after tightening
the mount back down after making the necessary adjustments it is extremely easy
to make the proper precise adjustment based on the TPoint information.
HINT:
Live Video Users
If you have a live video camera it
is quite easy to see what is happening when you are adjusting the mount in
real-time. For the price of a live video camera under $100.00 these are hard to
beat for polar alignment. By accurately centering a star you can see precisely
what happens to the stars position when you loosen the mount knobs to make
adjustments. Even when all 4 elevation knobs are loose and the mount is free to
be raised or lowered the star will stay put. After making an adjustment up or
down when you lock the mount down it again stays put!
The Final Adjustments - precisely calibrated with feed back
At the point where the polar
alignment numbers are very good, say 1 to 2 arcminutes in error or less you may
find it hard to make smaller than 2 arcminute adjustments. That is adjustments
that are smaller than the calibrated tic marks on the adjustment knobs 2
arcminutes.
By using TheSky's Motion controls as
a tool you can make very accurate adjustments at varying increments.
Here is exactly how! <----- Click here!
Note that by shooting for slightly higher than the pole
(the refracted position
based on your latitude ~90 arcseconds too high for 39 degrees north latitude) you have accomplished the same thing as
trying to use the King’s
Rate to help compensate for the effect of atmospheric refraction during
tracking. However, when employing
ProTrack
the polar alignment, the above off-set, along with many other tracking
related issues like flexure, out-of-roundness of the gears, refraction, and many
more can be completely taken care of by the low level TPoint tracking kernel
ProTrack,
so you need not be too concerned with the polar alignment when it is reasonably
small say an arcminute or less.
Azimuth Adjustment knob
2 arcminutes knob peak-to-peak
Azimuth adjustment
Side View of Knob
Elevation Adjustment
High point to high point on knob
Note the three large threaded holes
provided in the revolutionary elevation adjustment knob are to be used with a
“cheater” screw or threaded rod for more leverage. This maybe necessary for scopes that approach the 150 pounds weight carrying
capacity of the ME (150 lbs. for the OTA and 150 lbs. of counter weights for a
total of 300 lbs). Use one if necessary.
Note it is best to be slightly high
on the elevation tic marks first so you can then come down, that is drop the
elevation which is easier with a lot of weight on the mount.
That is because the weight is gently being lowered as opposed to fighting the
weight to accurately raise it. When the ME is accurately
leveled the tic marks on the mount are very precise and achieving an elevation
of 5 arc minutes from the pole or better before TPoint is reasonably simple.
If the telescope you are using is an
older model Paramount GT-1100 or GT-1100S the amount of one full turn in Azimuth
is equal to 12 arc minutes of adjustment. The Elevation is 15 arc
minutes/turn. Use the above amounts as a guide or see the alternative
method for accurate adjustments below.
If you have a "goto" telescope mount
that is supported by TheSky but it does not have precisely calibrated polar alignment
adjustments i.e. the mount wobbles when tightening the mount back down after
making adjustments, use live video as a
tool! For example if TPoint reports that
you need to make an adjustment that is 5.2 arcminutes to the West in azimuth and
3.0 arcminutes lower in elevation you can use the video to watch the amount of
adjustment being made.
First align your live video camera
with North Up and East to the left for proper orientation. Next, slew to a star
as close to the Celestial Equator as you can (Declination = 0 degrees). With
German Equatorial mounts keep in mind that crossing the meridian changes North
and South on the video. Next slew the telescope in Azimuth and Elevation
precisely the amount that TPoint is reporting under Model | Polar Alignment
Information. By using a star near declination zero you have the most amount of
right ascension allowing for accurate adjustments. The closer to the pole the
worse the adjustment becomes.
Location of Declination Zero
Celestial Equator - Declination Zero
Very near Orion's Belt
Example TPoint Polar Alignment Information
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TPoint reports polar alignment relative to the
true pole, not the refracted pole. If you're aiming for the
refracted pole, adjust the values reported by TPoint accordingly.
See "Optimum Location of the Polar Axis" in the
TPoint User's Manual
for a detailed description on how to adjust your mount to the
refracted pole.
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In this example, TPoint
reports the following information for the polar alignment (only after mapping
enough points as described above AND after adding the proper new
terms also described above). The relatively low sigma values indicate that you can
"trust" the data.
We are going to use the following
actual TPoint data to demonstrate.
Northern Hemisphere
************* AZIMUTH ************
MA: +15 seconds (+5.2 minutes).
Rotate axis West (counterclockwise).
For latitude 34.22°, the azimuth adjustment is 5.3 minutes.
Sigma=11.904
************* ALTITUDE ************
ME: -182 seconds (-3.0 minutes).
The polar axis should be lowered -182 seconds (-3.0 minutes).
Sigma=7.507
Use TheSky's
Telescope | Motion Controls dialog in the Altitude/Azimuth mode and
"JOG" the telescope as close to 5.2 arcminutes to the West and as close to 1.5 arcminutes South or down
as you can. With the Paramount ME the JOG will be extremely accurate.
First
pick the right amount to "Jog" the telescope. There should be enough increments
to suit any amount of adjustment here.
TheSky's Telescope
Motion Controls
TheSky's Motion Controls
Offset Slew Alt-Az
In the case of the elevation adjustment we are shooting for the
refracted pole which is about 1.5 arcminutes too high for a latitude of 40 degrees, as described earlier in the text.
These jogs must be made only after centering on a bright star near the
meridian at declination ZERO. Use a star at
declination zero as close to the Celestial equator as
possible. Use TheSky to easily identify such a star that meets the declination
requirements. See above. Also, note that you will have to adjust the "Jog" amount's
according to the amount of adjustments needed.
HINT: By using CCDSoft's feature to place the cross hairs on your CCD images
or piped in video you can easily center stars in the field! If you have
calibrated the CCD camera you can use CCDSoft or you can also use TheSky's
telescope motion control!
Nice! Click image for details!
After
the mount has been JOGGED the proper amount in Altitude and Azimuth (offset
based on TPoint values for polar alignment) use the
mount's polar alignment adjustments to bring the star back to center, as
accurately as you
can. That is, the mount is physically being moved in each direction as
needed to re-center the star making a precise calibrated polar alignment
adjustment.
If you have made very large adjustments to the
mount it may require a finder scope, flip mirror, Telerad (c) or other method,
to aid in placing the star back in the smaller live video field of view after
the adjustment. Or just
work in small moves (small moves Elly small moves - Contact).
When the star has been accurately re-centered using the mount's polar
adjustments that match the values reported by TPoint, you have made a near perfect adjustment limited primarily by your
ability to keep the star centered after locking the mount back in place!
Paramount ME users do not have to be concerned with this!
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