User's Guide to the Nickel Spectrograph


Table of Contents


Introduction
Hardware Overview
Aperture Wheel
Filter Wheel
Collimator
Grisms
CCD Stage
Flexure
Detector Characteristics
Software Overview
CCD User Interface
Motor Controller
Nickelfocus
Observing Hints
Calibration Lamp Spectra
Checklists

Mt. Hamilton Homepage

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.


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Last modified: Tue Jul 17 18:32:13 PDT 2012