B&C Spectrograph Refurbishment
B&C Spectrograph Weight and Dimensions
Undergraduate project: Jacob Stow, Tynan Weber
Our lab houses a Boller & Chivens (B&C) Cassegrain spectrograph model 31523 that was installed at the Cerro Tololo Inter-American Observatory (CTIO) in 1975. We are refurbishing it with modern controls and mechanisms.
The B&C Cassegrain Spectrograph Model 3153
The spectrograph manual provided to Observatorio Astronomico Di Brera by Boller & Chivens for the same model of spectrograph provides an overview of the instrument: "Light passes from the telescope through the slit and is collimated by an off-axis parabolic mirror. The collimated light is dispersed by a diffraction grating and is then reimaged by the camera onto the photographic plate. Other features include a decker, filter holder, provisions for an exposure meter, shutter, comparison light system, a 14 cm direct photography camera, and a 45 cm direct photography camera."
Refurbishment Plan
The spectrograph needs a motorized collimator dial, updated electronics, updated motors and motor control, and software control. Additionally, some subsystems should be disabled and removed from the workings of other subsystems. For example, the exposure timer controls the shutter, but modern detectors have their own exposure timers, therefore the shutter should be changed to have an independent controller.
Motorized Collimator Adjustment
The collimator was designed to be adjusted by hand with a knob at the lower end of the spectrograph. Changing to a motorized adjustment allows users to control the collimator using the control software. The collimator assembly is removed to add a motor to the mechanism.
The motor is a 57mm NEMA 23 Stepper motor, reused from an old 3D printer. The motor is connected to the focus mechanism by an RC-018 set screw shaft coupling and driven by a DRV8825 motor driver carrier that receives commands from a Raspberry Pi.
