Jason finished assembling our new CCD (and shutter) cooling system in the mirror lab yesterday. After several tries, and finally replacing the threaded cap that wouldn’t hold pressure, the system passed a pressure and operational test. It’s on its way to Pasadena, and from there to Chile.
The Shutter in Closed Loop Action
The Magellan AO VisAO camera includes a novel system for performing “frame selection”, which is the technique of using only periods of good seeing and/or AO correction in the final science image. Traditional “lucky imaging” does this by reading short exposures and selecting in post processing. In our system, we use measurements of Strehl ratio in real time and open and close the shutter based on those measurements. This video shows our shutter working with the AO loop closed in the Solar tower in Arcetri, Italy. It was taken during the week after our pre-ship review.
The Strehl time series is derived from our custom wavefront reconstructor (calculations are done on a GPU). During this testing the shutter decisions were based only on the most recent Strehl measurement, meaning that we did not use any predictive algorithms. Note the fleeting moments of a clear Airy pattern as the shutter finds the highest peaks in the Strehl ratio time series.
The real question is: does it do any good? We’re still analyzing all the data we took, but for now this demonstration is an important step showing that our telemetry and hardware systems can do real-time frame selection.
The shutter in action
Here’s a short video of our “smart” shutter in action. In this test it is responding to a simulated Strehl ratio time series, showing that it is fast and accurate enough to perform real-time frame selection – essentially lucky imaging without the luck.
This plot shows that the shutter was open when Strehl was high (red line up), and shut when Strehl was low (red line down). The 5ms delay is due to the mechanical delay of the shutter – it doesn’t move instantaneously. We are actively developing predictive algorithms to reduce this error.
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