The South African Astronomical Observatory (SAAO) is currently developing WiNCam, the Wide-field Nasmyth Camera, to be mounted on Lesedi, the observatory’s new 1-metre telescope. This paper discusses the design and results for the remotely-operated camera system. The camera consists of an E2V-231-C6 Back Illuminated Scientific Charge Coupled Device (CCD) sensor with 6144x6160 pixels, four outputs operating in non-inverted mode. This is to date the largest single chip CCD-system developed at SAAO. The CCD is controlled with a modified Inter-University Centre for Astronomy and Astrophysics (IUCAA) Digital Sampler Array Controller (IDSAC) utilizing digital correlated double sampling. The camera system will have full-frame and frame-transfer read out modes available with sub-windowing and pre-binning abilities. Vacuum through-wall PCB technology is used to route signals through the vacuum interface between the controller and the CCD. A thin, compact, 125x125mm aperture, sliding-curtain-mechanism shutter was designed and manufactured together with a saddle-type filter-magazine-gripper system. The CCD is cryogenically cooled using a Stirling Cooler with active vibration cancellation; CCD temperature control is done with a Lake Shore Temperature Controller. A Varian Ion Pump and Activated Charcoal are used to maintain good vacuum and to prolong intervals between vacuum pump down. The various hardware components of the system are connected using distributed software architecture, and a web-based GUI allows remote and scripted operation of the instrument.
SpUpNIC (Spectrograph Upgrade: Newly Improved Cassegrain) is the extensively upgraded Cassegrain Spectrograph on the South African Astronomical Observatory's 74-inch (1.9-m) telescope. The inverse-Cassegrain collimator mirrors and woefully inefficient Maksutov-Cassegrain camera optics have been replaced, along with the CCD and SDSU controller. All moving mechanisms are now governed by a programmable logic controller, allowing remote configuration of the instrument via an intuitive new graphical user interface. The new collimator produces a larger beam to match the optically faster Folded-Schmidt camera design and nine surface-relief diffraction gratings offer various wavelength ranges and resolutions across the optical domain. The new camera optics (a fused silica Schmidt plate, a slotted fold flat and a spherically figured primary mirror, both Zerodur, and a fused silica field-flattener lens forming the cryostat window) reduce the camera’s central obscuration to increase the instrument throughput. The physically larger and more sensitive CCD extends the available wavelength range; weak arc lines are now detectable down to 325 nm and the red end extends beyond one micron. A rear-of-slit viewing camera has streamlined the observing process by enabling accurate target placement on the slit and facilitating telescope focus optimisation. An interactive quick-look data reduction tool further enhances the user-friendliness of SpUpNI
The South African Astronomical Observatory (SAAO) is designing and manufacturing a wide-field camera for use on two of its telescopes. The initial concept was of a Prime focus camera for the 74” telescope, an equatorial design made by Grubb Parsons, where it would employ a 61mmx61mm detector to cover a 23 arcmin diameter field of view. However, while in the design phase, SAAO embarked on the process of acquiring a bespoke 1-metre robotic alt-az telescope with a 43 arcmin field of view, which needs a homegrown instrument suite. The Prime focus camera design was thus adapted for use on either telescope, increasing the detector size to 92mmx92mm. Since the camera will be mounted on the Nasmyth port of the new telescope, it was dubbed WiNCam (Wide-field Nasmyth Camera). This paper describes both WiNCam and the new telescope. Producing an instrument that can be swapped between two very different telescopes poses some unique challenges. At the Nasmyth port of the alt-az telescope there is ample circumferential space, while on the 74 inch the available envelope is constrained by the optical footprint of the secondary, if further obscuration is to be avoided. This forces the design into a cylindrical volume of 600mm diameter x 250mm height. The back focal distance is tightly constrained on the new telescope, shoehorning the shutter, filter unit, guider mechanism, a 10mm thick window and a tip/tilt mechanism for the detector into 100mm depth. The iris shutter and filter wheel planned for prime focus could no longer be accommodated. Instead, a compact shutter with a thickness of less than 20mm has been designed in-house, using a sliding curtain mechanism to cover an aperture of 125mmx125mm, while the filter wheel has been replaced with 2 peripheral filter cartridges (6 filters each) and a gripper to move a filter into the beam. We intend using through-vacuum wall PCB technology across the cryostat vacuum interface, instead of traditional hermetic connector-based wiring. This has advantages in terms of space saving and improved performance. Measures are being taken to minimise the risk of damage during an instrument change. The detector is cooled by a Stirling cooler, which can be disconnected from the cooler unit without risking damage. Each telescope has a dedicated cooler unit into which the coolant hoses of WiNCam will plug. To overcome an inherent drawback of Stirling coolers, an active vibration damper is incorporated. During an instrument change, the autoguider remains on the telescope, and the filter magazines, shutter and detector package are removed as a single unit. The new alt-az telescope, manufactured by APM-Telescopes, is a 1-metre f/8 Ritchey-Chrétien with optics by LOMO. The field flattening optics were designed by Darragh O'Donoghue to have high UV throughput and uniform encircled energy over the 100mm diameter field. WiNCam will be mounted on one Nasmyth port, with the second port available for SHOC (Sutherland High-speed Optical Camera) and guest instrumentation. The telescope will be located in Sutherland, where an existing dome is being extensively renovated to accommodate it. Commissioning is planned for the second half of 2016.