Hardware Overview
The Nickel Spectrograph mounts at the f/17 cassegrain focus of the
Nickel 1-m telescope. A number of different grisms are available to
cover the full optical range of wavelengths. A limited direct imaging
mode is also available. Nearly all the hardware can be remotely
operated from the Nickel 1-m control room.
A remotely selectable
aperture wheel containing fixed slits in
a variety sized, pinholes, and occulting
spots is located in the telescope focal plane (the telescope is focused
onto the aperture wheel by moving the secondary mirror). The apertures are
reflective and tilted with respect to the focal plane allowing a
periscope relay an image of the focal plane to the guide camera for
easy slit viewing and guiding.
A five position, remotely selectable
filter wheel sits immediately
below the aperture wheel. One position of the wheel (position 0) is always
empty. Up to four 2x2" filters can be loaded into the remaining positions. A
standard selection of broadband and order blocking filters are
stored at the Nickel. Additional filters are available from the Shane
3-m filter library.
The
shutter is mounted just below the filter wheel. There is no
minimum exposure time for shutter operation, but shutter timing errors
are a few milliseconds. The timing error on a 1 second exposure should
be less than 1%. Exposures of less than 0.5 seconds are not
recommended because the uneven illumination of the chip due to shutter
fly time becomes significant.
The
collimating lens is on a remotely controllable stage that
moves it up and down along the optical axis, to achieve the best
focus of the spectrum on the CCD.
The
grism tray is a four position slide holding up to
three grisms, position 0 being always clear.
A fixed
camera lens refocuses the light onto the CCD. Two camera
lenses are available, a 110mm Hasselblad and 58mm Nikkor lens. Only the
110mm Hasselblad lens is recommended for use. The focus of the camera lens
is fixed and should not be changed.
A manually operated
dark slide lies between camera lens and CCD.
It must be opened for all exposures other than darks and biases, a fact
routinely rediscovered by many observers on the first night of a run.
The
CCD and its dewar are mounted on an X-Y stage. The X motion
moves the CCD in the spectral direction, permitting the observer to adjust
the central wavelength. The Y motion allows the spectrum to be best p
ositioned in the spatial direction. The Y-stage is
manually operated while the X-stage is remotely operable but manually locked.
The current CCD (also known as dewar#9) is a Reticon 400x1200
array. The CCD response is enhanced and made more uniform by flooding
it with UV light during a complicated cooling procedure. Failure to
keep the CCD cold by neglecting to fill the dewar can result in loss
of sensitivity, requiring a laborious reflooding. Fringing can
be pronounced at the red-end of the spectrum with this detector.
Due to the length of the spectrograph, flexure is significant
(up to 5 pixels). Observers should consider this when taking data.
Where effective removal of fringing and/or accurate wavelength
calibration is needed, observers should take flat field and
line-lamp exposures at the same position as each observed object.
Support Astronomers (sa@ucolick.org)
Last modified: Tue Jul 17 18:32:13 PDT 2012
