Interlude: Installing new cold stops and a J-band filter into Clio2

Meanwhile, back in Tucson… We interrupt the NAS Fitcheck program to bring you this update on the Clio2 infrared camera.

After the Pre-Ship Review for Clio2 in Amsterdam in July, we have been completing preparations to receive diffraction-limited near-IR to thermal-IR photons from MagAO. Yesterday and today we installed the new J-band filter, and the cold pupil stops sized for Magellan. This was done in a CAAO lab at Steward Observatory in Tucson, where Clio2 is undergoing its final testing before shipment.

Cold pupil stops: Clio2 used to be “Clio” and was installed on the MMT telescope in Arizona. The MMT, like Magellan, is a 6.5-m telescope, but the Magellan secondary is 0.85m while the MMT secondary is 0.7m. Therefore, because the pupil is different, we needed two new cold stops for Clio2 on Magellan. A cold stop is a cryogenically-cooled metal mask located at an image of the telescope pupil, and its purpose is to block stray light (heat sources in the dome cause a lot of background thermal light) from contaminating the infrared image. Here is a picture of the pupil wheel with the new cold stops:

Clockwise from Phil's hand: 3-hole non-redundant aperture mask (NRM); 6-hole non-redundant aperture mask (NRM); Wide-camera cold stop (home); M-band apodized-phase plate (APP); L'-band apodized-phase plate (APP); Narrow-camera cold stop.

We also added a new J-band filter, taking out the old 3-5um Janostech filter from filter-wheel 1:

Clockwise from the red arrow: J (new), Blocked (for darks), Open (home), MKO M', Barr M, Direct vision prism, 3.1um, Barr L'.

We updated the Clio2 user manual at so that we can repeat this in Chile if need be.  Note the tools required: Most of the wrenches were found in a standard set of Allen keys, except for the 0.035” driver which is a special size.

Tools required for changing Clio2 filters: Phillips/flat head, 0.035, 5/64, 3/32, 7/64, and 9/64 inch Allen keys.

It took about 3 hours to take it apart and insert the new filter and pupil stops, including finding new spacers, etc.  It took about 1 hour to put it all back together.


T.J. Rodigas (foreground) and Andy Skemer (background) helped take Clio2 apart.

The box labeled 3 and 4 contains filter wheels 1 and 2. The box labeled 2 contains the cold pupil stops. We disconnected the wires and unscrewed the bellows (those keep the shafts straight at cryo temperatures) to access the filter and pupil wheels.

The same view as the previous image, with the filter and pupil wheels removed.

Two by two, hands of blue

Opening the pupil box to put in the new cold stops, and also Phil put in a new home switch. (Otherwise we could have just inserted the new cold stops through the port and not had to open it all the way.)

Oli Durney putting Clio2 back together


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