Spectroscopy, Gecko: The Coudé f/4 Spectrograph
Gecko: Focus of the 2
The first step of the LLLTV Focus procedure can be done during the
day. The rest of it needs a star, and should be done as soon as possible
after sunset, with a magnitude 4-5 star.
Get me back to the Secret page!
- In the control room, on the pannel that says ACQUISITION TV SYSTEM,
COUDE SLIT VIEWING:
- Switch ON the LLLTV camera (slit/field view) using the switch
called CAMERA POWER
- Switch ON the GAIN CONTROL
- Keep the gain to Zero using the dial.
- In the control room, on the OA's console, on the PRIMARY GUIDE
CAMERA CONTROL pannel, select the Coude camera, put POWER ON but keep
the intensity (gain) to zero.
- Before entering the outer Coude room:
- check that the Exposure Meter shutter is closed
- check that the gain on the LLLTV camera is at zero
- check that the gain on the Autoguider camera is set to zero
- Get a a walkie-talkie or portable phone to communicate with the OA
and observer (to change the gain on the cameras and change to Slit
View/Field View with Gecko)
- Get a small flashlight
- Procedure for LLLTV Focus (Slit view/Field view camera)
- (Daytime step) In the outer Coude room:
- put the TV screen ON (the switch is on the lower right of the
- On the right side of the rack, at the back of the room, there
is a select button with 3 positions, one saying SLIT, the other
saying A/G; select the SLIT position.
- Ask the observer to put the slit view mode
- Make some light (very little!), shining under M7
- Ask the OA to bring the gain of the LLLTV camera up, until you
see the black rectangle that is the image of the slit/slicer
- Unlock the sliding lens
- focus the slicer entrance slit on the TV using
the sliding lens.
- With a magnitude 4-5 star, and still in slit view, get the star on
your TV screen and ask the OA to focus the star using the telescope
focus; the focus value should be around 4540 (?) for a 0 celcius
temperature. The star will not focus to a spot, but rather to a
line that matches to the slicer entrance slit.
- Now with the telescope focused, ask the observer to change to
field view. Focus the star on the TV again using the adjustable lens
on the front of the camera.
- Change back to slit view and re-focus the slit on the TV using the
sliding lens again. When it is in focus, lock the sliding lens in
position. At this point, don't touch the adjustable lens on
the front of the camera.
- The LLLTV should now be in focus in both field and slit view
modes. This procedure should be re-done every time the filter in front
of the LLLTV is changed.
- Procedure for ISIT Camera Focus (Autoguider camera)
With a star focused on the slit, look at the image on the ISIT
camera. Adjust focus using the large silver-colored vernier on the
mounting stage of the ISIT. This focus will need to be adjusted if the
filter in front of the ISIT camera is changed.
Send comments to: Nadine Manset
Copyright © 1996, 1997, 2000. CFHT Corporation. All rights