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Researchers at the Department of Energy’s SLAC National Accelerator Laboratory have captured 3,200MP images, the largest photos ever captured in a single shot. The camera, an array that contains 189 individual image sensors, will become the future camera of the Legacy Survey of Space and Time (LSST) telescope at the Vera C. Rubin Observatory in Chile. The camera will be used to help shed light on some of the most intriguing mysteries of the universe, including dark matter and dark energy.
The 189 image sensors are charge-coupled devices (CCD) and each capture a 16MP image. To build the image sensor array, nine CCDs and supporting electronics were assembled into square units, called science rafts, by the Department of Energy’s Brookhaven National Laboratory and then shipped to SLAC. Then the team at SLAC inserted 21 of these square units into a grid to hold them in place.
The completion of the image sensor array and focal plane earlier this year took six months and proved to be a difficult task. In order to maximize the imaging area of the array, the gaps between individual image sensors are less than five human hairs wide. If the sensors touch each other during the process, they could easily break. Damaging a sensor or raft would be costly, as the rafts cost up to $3M USD a piece. SLAC mechanical engineer Hannah Pollek said of the assembly process, ‘The combination of high stakes and tight tolerances made this project very challenging. But with a versatile team we pretty much nailed it.’
The focal plane features impressive specifications beyond even the 3.2 billion total pixels. The pixels themselves are about 10 microns wide and the focal plane itself has been constructed to exacting standards. The focal plane is nearly perfectly flat, varying by ‘no more than a tenth of the width of a human hair’ across its more than two feet of width. The optics through which light will reach the image sensor array is designed to allow the sensors to identify objects 100 million times dimmer than what the human eye can see. This is equivalent to being able to see a lit candle from thousands of miles away.
The images produced by the 3,200MP camera are so large that you would need nearly 400 4K UHD televisions to display a single image at its full size. The resolving power of the camera would allow you to spot a golf ball from about 15 miles away.
As mentioned, the camera will be installed at the Vera C. Rubin Observatory in Chile. Once it has been installed, it will capture panoramic images of the southern sky every few nights for 10 years.
Steven Ritz, project scientists for the LSST Camera at the University of California, Santa Cruz, said, ‘These specifications are just astounding. These unique features will enable the Rubin Observatory’s ambitious science program.’ Over the course of a decade, the camera will capture images of about 20 billion galaxies. Ritz continues, ‘These data will improve our knowledge of how galaxies have evolved over time and will let us test our models of dark matter and dark energy more deeply and precisely than ever.’
Before the focal plane can be used within the Rubin Observatory’s program, it needs to be rigorously tested. This includes capture images of a variety of objects, including a head of Romanesco broccoli. In order to operate normally, the sensors must be cooled to negative 150° Fahrenheit. Without a fully assembled camera, the team at SLAC used a 150-micron pinhole to project images onto the focal plane.
SLAC’s Aaron Roodman is the scientist responsible for building and testing the LSST Camera. Of the successful test images, he says, ‘Taking these images is a major accomplishment. With the tight specifications, we really pushed the limits of what’s possible to take advantage of every square millimeter of the focal plane and maximize the science we can do with it.’
Despite the successful tests, there is much more work to do. Over the next few months, the team will insert the cryostat used to reduce the temperature of the image sensors along with the focal plane into the camera body and add lenses, including the world’s largest optical lens. The team will then affix a shutter and a filter exchange system so that the camera can be used to capture the night sky in different colors. The team anticipates the SUV-sized camera to be ready for final testing in mid-2021 before it begins its final journey to Chile.
JoAnne Hewett, chief research officer at SLAC and associate lab director for fundamental physics, says, ‘Nearing completion of the camera is very exciting…It’s a milestone that brings us a big step closer to exploring fundamental questions about the universe in ways we haven’t been able to before.’
As one would expect, we are unable to display 3,200MP images here on the site. However, SLAC has five full-size images taken with the focal plane of the LSST camera which you can view at the links below: