Monday, August 22, 2016

Wave-plates & field lens back in!

Popped in at SALT late in the afternoon, just in time to catch Jono handing the whole wave-plate mechanism to Keith, who was sitting underneath the RSS.

Serving up a wave-plate assembly
With the wave-plates re-installed, the last of the cleaned & re-filled collimator optics, the field lens group, could go back in as well.

The wave-plates fit between the main group & the field lens group of the collimator
Ockert could then check the overall alignment of the optics against the references that were established before the optics were removed.

RSS showing off all its nerves & blood vessels
That completes the RSS optical service part of the shut-down - great stuff guys!  Look forward to seeing the improved throughput of the spectrograph when we get back on-sky :)

Sunday, August 21, 2016

A few more of SALT's optics

Before all the action starts up again tomorrow, here's a chance to introduce a couple of the other important optics at SALT...  Here's a glimpse down the SALTICAM lens barrel.

Hello SALTICAM
& this beast is the ADC - the atmospheric dispersion compensator that sits just above the SAC, below the payload.  It consists of two large wedge shaped prisms, the separation of which can be changed to correct for the different extents to which the atmosphere bends red vs blue light.

The ADC getting some TLC from Janus
This is the moving baffle that lives above the ADC & blocks out stray light that's not followed the telescope's optical path.  The green reflections are due to the coatings on each of the prism surfaces. 

The carbon fibre moving baffle on top of the ADC housing

Saturday, August 20, 2016

Saturday eagle encounter

Drove up the hill for a walk this afternoon & spotted one of the eagles sitting on a rock on the SE edge of the plateau.

Enjoying the view out to the east, with Salpeterkop in the background
Strolled to within about 200 metres of it before it decided to take off & head home down the cliff to the south.

Time to go!
Those first few wing-beats are hard work...

About to disappear below the ridge
A stunning day up here - hard to believe the weather's due to pack up tomorrow, there's even snow forecast!

Friday, August 19, 2016

A well-deserved break for the team

The field lens group was cleaned & its fluid replaced this morning.  But now it's the weekend, after a very busy & productive week at SALT.  Time for the team to take a bit of a breather before finishing the RSS optical service & gearing up to re-install the payload next week.  SALT Operator Fred's up here now to run SAMS at night (weather permitting!), but otherwise it's pretty quiet for a change...

Papa black eagle on guard duty above the cliff this afternoon

Thursday, August 18, 2016

Collimator triplet oil change!

This morning the guys drained the collimator triplet & replaced the lens fluid in the 2 gaps.  Like last time, the scene was quite gruesome!  The problematic original lens fluid (which has vastly different specific gravity to the new type of fluid that's been in use since 2011) still refuses to leave the system.

Draining the coupling fluid out of the gaps in the triplet
Here's the replacement fluid slowly going in...  As the gaps fill up, most of the evidence of the old fluid disappears again.

Lens fluid transfusion in progress
The finished product looks Really Fantastic!

Sparkly triplet with surfaces cleaned & lens fluid replaced
The throughput measurements were repeated after the fluid change & showed an additional 2-3% increase blueward of 3700 A.

Before cleaning (red), after cleaning (blue) & after fluid change (green) throughput measurements for the main group
Having completed the post-fluid-change measurements, the main group was re-installed in the instrument.

Putting the main group back in this evening
The main group & field lens assemblies go into the spectrograph from below.

Jono making sure everything's lined up properly
The lens barrel is supported on a wooden frame that's carefully positioned & then slowly jacked up on a lifting platform.

Almost there - soon to be bolted into position
With that, it was time to get started on the field lens group.  A relatively simple assembly consisting of a fused quartz bottom lens (L1) & a calcium fluoride one above it (L2), with a small fluid-filled gap in between.

The calcium fluoride (L2) lens in the RSS field lens assembly
The dirty assembly was rigged up to the throughput testing system, which consists of a broadband light source, an iris to control the beam size, various combinations of lenses (to re-image the source for each group to be tested), an integrating sphere to even out the light distribution & an extremely handy little spectrograph that Ted donated from his old lab.  The optic under test is mounted on a pneumatically actuated stage that places the lenses in & out of the beam to produce the differential measurement (a huge upgrade over the old system that relied on a person sitting in the dark actuating the stage!).  The even more significant improvement is the fact that the throughput measurements over a broad wavelength range are now in the form of spectra obtained at various grating angles, rather than photometric data taken with a set of manually deployed filters.  Janus has also written a data pipeline to painlessly calibrate the spectra & display the throughput results - brilliant! 

The new throughput testing system, with the RSS field lens group installed
Here's the profile view of the field lens group in the beam.

A bit of a tight fit
This is almost the photon's view of the setup...  The light source is in the lower right corner of the image & the lab spectrograph is visible in the background on the right.  A set of "before" measurements was taken this evening so that the cleaning can be done first thing in the morning...

Field lens group in beam in the throughput testing system
While this setting up was going on in the clean room, most of the team was still busy with various tasks in the spectrometer room - only about 11 hours after they showed up here this morning!

Tell us a story Uncle Paul!
The notoriously tricky slit-mask mechanism was putting Thabelo & co. through their paces...

Feeding the monster
2.5 weeks into the shut-down, things are still on schedule & going well - great work by all concerned!

Wednesday, August 17, 2016

Cleaning the collimator main group

The next bunch of RSS lenses to be attended to was the collimator main group - the most complicated of the lens groups.  This unit contains 2 singlets + a triplet consisting of a sodium chloride lens (yes: SALT!), sandwiched between 2 spectacular chunks of calcium fluoride, with coupling fluid filling both the gaps (the butter in the sandwich, if we're inclined to overdo the analogy).

A dusty eyeball
The collimator doublet leaked some of its lens fluid at some point & this oily liquid had found its way down onto the top of the triplet - seen here as the messy streak at 6 o'clock.  Ugh :{

We've found the mystery smudge!
A set of "before" throughput measurements was made on the dirty main group, then Ockert could dive in & do his cleaning magic.

Okkie super-focused on the task!
The powerful combination of sodium lauryl sulphate, de-ionised water & alcohol once again did the trick, even removing the nasty streak of dry lens fluid.

Washing windows
The curvature on the top CaF2 lens in the triplet is really extreme!

Going after those hard-to-reach places
With the outer surface clean, one can more easily see the small droplets of the original lens fluid that still stubbornly refuse to mix with the new coupling fluid.  Fortunately these don't seem to have a huge effect on the optical performance.

Streaks & droplets of the original lens fluid are impossible to remove
The throughput tests were repeated after the cleaning & showed a huge improvement across the entire wavelength range - a gain of approximately 8%!  Awesome :)

Throughput measurements before (red) & after (blue) the cleaning of the main group
An already brilliant day that'd included thunder, lightning & loads of rain (technically impossible in the middle of winter!) + excellent throughput gains got even better when Ockert spotted a meerkat through the north window of the control room!  The more we looked, the more of them we saw & pretty soon a bunch of us were staring at a bunch of them.  From the pic below, one might argue that they were staring at us!  Absolutely delightful creatures :D

Who's watching who?!
So there you have it - we're finally starting to develop SALT/MeerKAT synergies!  We haven't seen these little guys out here before, but presumably they're heading north towards Carnarvon to go run their telescopes?

Tuesday, August 16, 2016

A new telescope in the family!

While Ant waits for various RSS mechanisms to become operational again & thus testable with the software, he's getting plenty of drawing/painting done!  Here's another view of the plateau, looking towards the south this time.  

Another angle on the plateau
The middle dome in that scene is the site of much excitement & activity as the SAAO's beautiful new 1-m telescope was installed in there earlier this month.  

The installation began on 2 August
Hannah's quiet but absolutely heroic efforts in leading this project, along with the dedicated APM Telescopes team + great support from numerous SAAO staff has made this wonderful new facility a reality.

The telescope was engineering-operable within 2 days!
The weather played along & First Light was achieved on Thursday 4 August.  An enthusiastic crowd visited the dome the next night & delighted in seeing New Blue in action!

New Blue begins exploring the southern sky
Saturn through the eyepiece was truly spectacular - thanks in no small part to the corrector optics that Darragh designed for the telescope...  Well Done to the whole team & thank you for sharing the excitement with the rest of us :)

A cellphone pic of Saturn through the eyepiece!
We wish you the best of luck with the extensive list of commissioning tasks that lie ahead!