As you know, we have been working on an all-refractive camera for the Hydra Bench Spectrograph. This camera, called The Bench Spectrograph (Red) Camera, has the advantage of no central obstruction and sophisticated multi-layer anti-reflection coatings. Recall that the Simmons camera has a significant central obstruction that blocks ~40% of the light in the fairly uniform beam produced by fiber scrambling. Note also that the glass and coatings on the Bench Spect Camera are optimized for the wavelength interval 4500-10000 A.
Our deployment of the Bench Spectrograph Camera was delayed by the fact that the WIYN CCD T2KC is warped and the Camera has a narrow depth of focus. In order to overcome this difficulty, a new final element was fabricated in order to optimize the coincidence of the focal surface of the camera with the measured shape of the CCD. I am happy to report that this fix has been quite successful. The images are very good (~2.4 pix FWHM) over 90% of the CCD. There is some degradation in the lowest and highest rows. We list below the grating configurations that we have tested the new camera with. This includes all of the on-blaze configurations that make sense redwards of ~4000 A.
Note that because the camera is fully refractive, the position of the best focal surface is a function of wavelength. In practice, that means that we have a tilt adjustment for the CCD dewar with respect to the final element of the camera (referred to as the dewar azimuth). As part of our testing, we determined the optimum dewar azimuth for all of the tested gratings (listed below). The recommended procedure is to set this dewar azimuth, and then to perform a focus sequence in dewar-camera spacing (as usual). Select the best focus for the spectral region of interest. Focus steps of two thousandths of an inch are recommended, and the final focus should be interpolated to 1 thousandth. Configurations well off blaze will likely require an adjustment to the tabulated dewar azimuth. Since determining the optimum dewar azimuth is time consuming, significant extra time should be allowed for such setups. We plan to augment our knowledge of the optimum dewar azimuth through experience.
We have observed numerous flux standards with the new camera and various gratings. Due to other commitments, these are not fully reduced. Initial indications are that the Bench Spectrograph Camera is ~2X more efficient at ~7000A than the Simmons Camera. We plan to incorporate all our information on efficiency, etc. in the Hydra manual as time permits. Note that wavelength coverage, resolution, etc. with the Bench Spect Camera are currently available via setup.f and Table 1 in the Hydra manual.
In order to allow users to make full scientific use of this new capability, we are releasing the Bench Spectrograph Camera for shared-risk use. For now, we only recommend observations that concentrate on the wavelength region 4500-10000 A. We also recommend only configurations listed in the Table below.
The following individuals have been trained to set up the new camera and counsel users during this set up: Jim De Veny, Daryl Willmarth, Dave Sawyer, Di Harmer and Bill Binkert.
One note of caution regarding changing between the Simmons and Bench cameras. This is a time consuming job that should not be done during the night. The WIYN operations staff may wish to limit the number of camera changes per run to one, since the changes do require significant time and the presence of one of the above trained personnel. Note that during the design of the camera we did take numerous steps to enhance the rapidity and safety of camera changes.
I am very grateful to the large number of people at NOAO who have worked on this project over the years. Let me single one out for special thanks: the project engineer, David Vaughnn.
We will be most interested in your comments and questions on the new camera. Please stay tuned for more information on the new camera being included in the Hydra manual.
Grating Order Angle Central Blue Red Dewar Az(degrees) 316@7.0 1 21.953 7401 4729 10105 1.310 600@13.9 1 28.900 7735 6306 9166 0.808 860@30.9 1 38.672 9019 8026 9999 0.638 860@30.9 2 41.523 5016 4523 5500 -0.360 1200@28.7 1 43.701 7731 7029 8419 0.293 316@63.4 10 68.900 5633 5479 5768 -0.128
Note: dewar azimuth not expected to be a function of order for the echelle due to the narrow wavelength interval covered. We have only tried 10th order so far.
Queries about this camera should be directed to Taft Armandroff (tarmandroff@noao.edu).
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Last Updated: 8/2/99, wiynq@noao.edu