After the mounting of Turpol ,
remember to balance the telescope by typing the command coun-wei
0.12 which means setting the counterweight height. Better even:
power on TCS, put telescope to alt-pos 55 and open mirror
covers. Look at the motor current readings in TCS status page #3
and adjust the counterweight height manually.
Locate the grey NEC portable PC, which is used to run the software for
the diaphragm viewing with the ST-4 CCD .
Most likely it is found in the Turpol cupboard.
Make sure that the CCD, which is permanently mounted on the Turpol
eyepiece, is connected to the multiplexer in the adapter at the port
Turpol STV. In the control room to the right of the Tamar PC
you will find the serial cable to connect to the portable PC. Turn on
the PC (on the left-hand side). Follow the description on the piece
of paper taped onto the laptop. The use of the camera is described
Using the ST-4 for Turpol Diaphragm Viewing .
Ikegami TV monitor from the metal cupboard in the control room and
connect the coaxial cable marked Turpol STV to it.
Test that the diaphragms can be seen on the TV screen.
Mark the diaphragms on the screen. Then select diaphragm #3 (open
position) and check the alignment of the chopper by integrating for
a few seconds with the diaphragm illumination on. It should be centred
between the two diaphragms. If you need to adjust it, note that
turning the knob clockwise moves it towards the left on the screen.
(To actually move the chopper pull the knob towards you and then turn.
The outer part of it is completely loose.)
Make sure that the dark slide is closed
(knob in OUT position), and check that both high voltage power supplies
are turned down to zero and switched off. Switch on the CAMAC crate
(button at bottom left of the unit). Then power on the high voltages.
This should be done 3-4 hours before observations start.
NB! Make sure the knobs are turned down to zero before switching on!
The UBV supply should be at -1150 V and the RI supply at -1800.
Turn them up step by step, and do not put too high a voltage on
the tubes, as this will cause permanent damage! Also, do not
power on in humid conditions! If the whole day has been very wet,
one might encounter leakage problems.
Typical dark current counts (per second) are found to be 0-5 in U,
10-20 in B, 0-10 in V, 30-70 in R, and 10-50 in I. These can checked
on the data acquisiton computer when having started the pp
program. Scroll between the channels by clicking with the mouse on
the two central lower fields. If the count rates for R and I dark
current reach 200 it means that the cooling is not working.
When it is dark:
Having opened the dome and started up the TCS, switch on the guide-TV
on the TCS by typing tv-on and set auto-pos-full
for automatic guiding if not already set. Point the telescope to a
bright star (FK5 or so). Select diaphragm #3 (open) on Turpol to see
a bigger field. If you don't see the star, nor the scattered light
from it anywhere, then stop guiding (ag-off) and step the
telescope (use o-s 3 3) to move the guide star a bit towards
the upper right on the guide tv screen. Now you should see the star on
the Turpol TV image. Put in the diaphragms, use o-s 0.5 0.5 and
step the telescope until the star is in the center.
When the star is nicely centred in the diaphragms, mark the position
of the guide star on the guide monitor. Move the guide star box
position to the guide star with the command star-box-pos x y
where x and y values should be close to 310 and 140. Start guiding
using relaxed guiding ag-rel. On subsequent pointings the star
box will not be moved and by using auto-pos-full a correction
is made to pointing
errors, such that the target should land in the diaphragms (roughly)
when the correct(!) guide star is moved into the star box. Show the
observer this step, as the star-box-position is set to centre when
the telescope is powered on. (This should be included in a
Now adjust the telescope focus (foc-pos <xxx>) in such a
way that the image in the right hand diaphragm (the extraordinary ray,
which is slighty astigmatic) gets as round as possible. Default focus
for Turpol is 24350. The default guide camera focus is: 650. It is probably best to set manual-tv-focus
on the TCS for the time being.
Optionally, you may now check where the target lands on the
guide TV for future finding of a faint target that is not easily seen
through the turpol diaphragms. Do this with the
commands tv-fi g, tv-foc 600, and g-p-c. Now the bright
star should be a bit to
the upper right of the centre of the TV monitor. Mark its position with
a felt tip pen.