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Observing Plan | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Observing Result | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Slew/Centering Performance | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Dome Slewing Performance | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Sky Conditions (Locate Frames) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Night Sky Summary Plot Top axis: Sky Brightness at Zenith (in ADU/s) Lefthand axis: Local Time (hh LT). Righthand axis: Sun Altitude (degs) |
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Pre-Session Weather Forecast (API data from darksky.net) Forecast showed initially cloudy clear with some rain, but then clearing after midnight. Wind quite strong In the event skies rain stopped at 17:00 and skies at 20:00 Observatory opened at 22:07 and Polar Alignment, BackLash Testing was conducted. Main session was started at 02:20 and continued until 05:37 when session suspended due to passing cloud and overall reducing star count. |
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Session Event Log | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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PHD2's Drift Align Tool was used at start of session to try to improve polar
alignment and thus improve autoguiding performance.
Used images from the ZWO
ASI 178MC camera attached to the 80mm GuideScope. Images are orientated
North Up, East Left.
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PHD2's Guiding Assistent was used to measure the LX200 Mount's Declination
Backlash at a number of sky points.
These were all done using Guide Speed
x0.66 (ie. a guide speed of ~10 arc secs/sec)
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Latest development version of PHD2 (v2.6.6dev3, dated 2019-12-07) installed onto Observatory and Office Computers
https://openphdguiding.org/development-snapshots/
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2" Field Flattener and Corrector (TSFLAT2) from TS-Optics (Germany) was
installed on the secondary scope today, along with necessary extension tubes to
connect to my existing Orion X-Y Star Finder & ZWO ASI 178MC Camera.
(the prime purpose of the flattener/corrector is to obtain high quality off-axis
imaging is a setup where the camera sensor is deliberately placed off axis to
allow the secondary scope to be perfectly centered on the same FOV as the main
scope)
The 2" flattener (TSFLAT2) was purchased instead of the larger 2.5" flattener
(TSFLAT2,5) because it was
a) significantly cheaper ( 179 vs 289 EUR),
and is more than adequate for size of the CMOS sensor on my ASI 178MC
camera
c) allow easily swapping in of Herschel Wedge for Solar Imaging
(centered in optical field and does require flattener)
My TS 80mm f/6 APO Scope has a 480mm focal length. For focal lengths of
450 to 490mm the Field Flattener requires 123mm separation distance from
the camera sensor for optimal flattening. (Product
Page on Teleskop Express Website). With my 178MC camera and Orion XY Finder
have a combined backfocus of 50.5mm, so I needed 72.5mm of extension
tubes. I didn't purchase the TSFLAT2A extension option (where online shop select
the items for your setup), but instead selected the extension items myself.
--------------------------------------------------------------------- Back
of 2" Field Flattener
30.0mm (TSVF230, 30mm
Extension tube, 2")
6.0mm (TSM48i-T2a,
Adapter, 2" to T2)
26.0mm (TST2V26,
26mm Extension Tube, T2)
10.0mm (TST2V10,
10mm Extension Tube, T2)
38.0mm (Orion XY GuideStar
Finder, T2 to 1.25"
12.5mm (ZWO ASI 178MC Camera,
1.25" nose)
--------------------------------------------------------------------- Camera
Sensor
122.5mm Total (vs 123mm Required)
The 30mm Extension Tube
allows the field flattener to pushed further into the telescope back tube if
required or lfor ater optimisation. As there are no natural stops on the
2" flattener & extension tube a Baader Hyperion 2" parfocal ring was added to
allow consistent placement of the assembly within the telescope's focuser. This
will assist the swapping in/out with 2" Herschel Wedge for solar viewing,
without loosing track of the focus position.
After installing the new TSFlat2 Field Flattener a careful check was made
to ensure that the guiding/imaging train was absolutely locked tight and rigid.
Whilst the majority of the train was rigid there was movement of the camera in
the Orion XY Guidestar Finder, relative to the T2/2" extension tube & telescope.
This is due to slight play in the XY Guidestar Finder unit associated with the
mechanical components that enable the XY Offset. This was resolved by using two
small clamps to rigidly hold the two parts of the XY Finder together and take out
all the play.
Small clamps added to take out play in Orion XY Guidestar Finder |
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As part of checking out large and variable Declination Backlash (see
Declination Backlash Measurements above) the Declination Drive Cover was
removed from the right hand fork arm in order to examine the Declination Drive.
The movement of the Declination Drive Unit and its tension against the large
Declination Gear seemed normal. It would have been nice to a) reduce
the travel distance of the drive unit using travel limit screw and b) insert a
small washer to increase the spring tension, but it wasn't possible to apply a
enough leverage to move the screw using a small hexagonal allen key with risk of
breaking the key or stripping the hexagonal slot on the screw.
In the
process of loosening and removing the Declination Knob it was noticed that the
scope is badly out of balance, which was expected and is the most likely cause
of the very the variable declibatiion backlash & associated poor guiding in
declination
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As part of checking out the large and variable
Declination Backlash (see above) and associated poor autoguiding performance
the Balance of the LX200 Main Scope was re-checked.
(this was done
after installing new 2" Field Flattener on secondary scope, see
2" Field Flattener, TSFLAT2)
The LX200 Scope was previously balanced when it was installed in
Observatiory in May 2018 so that the OTA tube was balanced with the tube lying
horizontal when pointing due south. This is at a position where scope is
pointing at Declination -32°. In practice this is of course never a position
where autoguiding/imaging is ever active; for all positions (Dec -25° to
+66°) where autoguiding/imaging is actually employed the scope is out-of-balance
(being only moderately balanced for Dec -25° to +10° & very poorly balance for
Dec +10° to +66°)
The poor balancing iof the OTA tube was very noticable
when the Declination Knob and Cover were removed to check Dec Drive Unit. The
OTA 'demands' to point vertical pulled down by the weight of the heavy SBIG
Camera/Filter Wheel & TCF-S Focuser.
To improve balance two things were changed
a) the counter weights below
the OTA (cylindrical weights plus two lead-weighted ankle exercise weights) were
pushed as far forward as they would go.
b) the guidescope was pushed slightly
further forward
Checks following the these two changes shows that the OTA is now in balance when scope pointing at Dec 0° (Altitude 32° when pointing due south. When position horizontal the OTA noew tries to point downwards, when tipped up (Alt 45°) the front of the scope still tries to pull towards zenith but not as badly as before. This means the scope if now very well balanced when pointing at Dec -10° to +10°, moderately well balanced for -10° to -30° and +10° to +40° and only poorly balanced for Dec +40° to +66°. This is still not perfect but at least a lot better than before.
The OTA balance will be improved further when the AO-8 adaptive optics unit (no longer needed) is removed from the scope. This will reduce weight at the back of the scope in two ways, directly from removing the 0.6kg unit and indirectly by bringing the heavy SBIG ST-10XE camera closer to the scope
Forward Plan
- Repeat Backlash Measurements
>> To be done at next session
- Look at adding further weights below OTA in order to achive
improved balance when OTA tube in vertical. At present the scope
is top heavy . Options are i) extra ankle weights and ii) extra weight bar.
Done 2019-12-14 (see LX200 Rebalancing (2)
)
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As part of checking out the large and variable Declination Backlash (see above) and associated poor autoguiding performance some improvements in telescope balance were achieved by moving the counterweights below the OTA further forward, and moving the piggybacked secondary scope further foward (see LX200 Re-Balancing (1) ).
Whilst this improved the balance, the OTA was still too top-heavy, especially
when the scope was pointed vertical. To get better balance the 3D weight
system from my old 8" LX200 Scope was requisitioned. In order to fit
onto the rail on my 12" LX200 Scope the hole on the circular metal cylinder had
to be drilled out to 15mm diameter (from ~ 13mm). The weight system
only had one remaining weight and until some additional weights arrive, a leaded
ankle/wrist exercise weight was used to provide the necessary weight allowing
balance to be achieved with the OTA tube both vertically and horizontally.
Balance with OTA tube vertical still needs a little bit of tuning but this
will be done after an upcoming modification to the irmaging train to take out an
AO-8 adaptive optics unit. The latter will reduce the weight at the back
of the scope in two ways, directly from removing the 0.6kg unit and indirectly
by bringing the heavy SBIG ST-10XE camera closer to the scope
Forward Plan
- Review balance again after
removing AO-8 unitpeat Backlash Measurements
>> Waiting on modification to imaging train
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PHD2's Guiding Assistent was used to re-measure the LX200 Mount's Declination
Backlash at a number of sky points, following re-balancing of the scope (see
LX200 Rebalancing (2) )
These were all done using Guide Speed
x0.66 (ie. a guide speed of ~10 arc secs/sec) and with anti-backlash (Dec)
disabled (i.e. Autostar II setting of 0)
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PHD2's Drift Align Tool was used to check polar alignment after adjustments
made in last session
(see Polar Alignment -
Measurements and Adjustments, 2019-12-10) .
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This Web Page: | Notes - Session 728 (2019-12-10) |
Last Updated : | 2024-02-20 |
Site Owner : | David Richards |
Home Page : | David's Astronomy Web Site |