A fairytale end to a loooong slog!

After quite ordinary weather all of yesterday, things started to improve around sunset - first we were treated to a black eagle flyby & then the sky cleared up :)  The seeing was also better than we've had up here in a long time & so it was that IQ's last night turned out to be a particularly memorable one... 

It was cool too having Paul learning the ropes - seen here receiving the SALT Astronomer Force from The Master, Petri!

But the highlight of the night, & indeed the culmination of the enormous IQ effort, was obtaining this magnificent image (with a freshly stacked primary mirror & great seeing) - stars with full width half maxima of 1.1 arcseconds over the entire field of view!!

We were ready to celebrate with the images obtained the night before, but it was a great privilege to be able to see what the telescope's capable of in good seeing - truly a fairytale end to the IQ campaign!

The big bottle has joined the collection that's marked previous milestones in SALT's life & there will no doubt be more to follow as we edge closer to full science operations over the next 6 months :)

All packed up & ready to go home, Darragh was readily coerced into leaving a note on the front door for the Tech Ops Team that'll be in first thing tomorrow morning...

A picture that's worth a thousand words/hours/days!  & for those who want more of the gory details, see Darragh's latest IQ report to the SALT Board.

We'll be back in about a month or so to throw the party to end all parties!  In the meantime, good luck with the rest of the work guys - it's been an *Absolute Blast* working with you all, it's with heavy hearts that we leave you & this very special place...

Before & After!

Perhaps it's a bit late to be describing what the problem was, but since starting the on-sky testing we've dug out old images & it's worth looking back...  The most serious contributor to the SALT IQ nightmare was the focus gradient, which meant that only a small portion of the 8 arcmin field could be kept in good focus at any given time.  By adjusting the telescope's focus, different parts of the field could be optimised, but always at the expense of other regions.  This in itself was unacceptable, but the focus gradient also exposed a variety of other horrors, including mutilated stars in regions that were out of focus & severe astigmatism.  Finally, there was the hideous notion that all of these woes somehow vary unpredictably due to a combination of factors...  Below is a typical bad IQ image, obtained with the Apogee camera in late September 2007.  Best focus is in the top right corner, the bottom left corner shows the mangled stars & overall the whole lot's just a Mess!

Fast forward through years of extensive detective work, the formulation of an extremely thorough repair plan, the 16 months it took to execute the plan & then wait for mediocre observing condtions to get the image below...  Uniform IQ over the entire field of view - The Focus Gradient Is Gone!! :) :) :)  But the good images aren't stable over time & one can see strange things going on when you take the telescope out of focus - the doubled images that we've dreaded all along!

That's where the auto-collimator instability came in & after fixing up the mount & then attaching the whole lot to the steel collar of the SAC, we obtained really beautiful images last night!  Still no focus gradient & after optimising the auto-collimator offsets, they didn't need to be tweaked throughout the night - the images weren't doubled or distorted any more :)  

What remains is a small amount of astigmatism, which we now know has to reside within the primary mirror (since we've fully re-aligned the SAC & tested the surface figures of its mirrors & found them all to be in great shape).  So that's the next step, but we're down to the finishing touches now! :)

SALT's looking like a telescope again!

We opened up the shutter just before sunset & enjoyed the photography-friendly light while the tracker cast shadow-monsters on the inside of the dome...

Yesterday Jonathan put in four more (very clean!) mirror segments near the bottom of the array.

Eben & Martin installed various dial-gauges (visible just to the left of centre in the image below) to measure the amount of movement between the steel and aluminium collars that attach the SAC to the payload.  Happily, these readings were only of the order of a couple of microns.

The major intervention today was to move the auto-collimator, previously mounted on the NRS, to a new attachment point on the bottom of the steel collar that's bolted to the SAC itself.  The small silver tube can be seen just above the SAC in the pic below.

This ought to improve the stability of the auto-collimator & since the sky looks good, we hope for healthier images later tonight!

Beefing up the auto-collimator mount

During the day Eben & co worked on making the auto-collimator mount a lot more stable than it was & conditions at the start of the night looked promising...

Sadly though, these were the best star images we managed all night, thanks to rapidly deteriorating seeing & then the arrival of a nasty cold front!  SIIIIGH :(

Farewell to a Cape Town landmark

After another frustrating night of hopelessly bad seeing, we packed up & drove back to Cape Town the next morning.  Coming in on the N2 we got a last close-up look at the Athlone cooling towers scheduled to be imploded the next day.  Thanks Tim for snapping this pic while I was driving!

Much of Cape Town turned out to watch, making traffic in the areas with the best views impossible, but a bunch of us watched from the roof of the SAAO.  A brief squall distracted everyone & prompted the demolition team to flip the switch about 4 minutes early - we were lucky to catch any of the action at all!

WOW :)  Google "Athlone cooling towers" for some great YouTube videos of the event!

Encouraging, but puzzling too...

Despite it still being gloomy & overcast by lunch time, the sky cleared up beautifully through the afternoon & straight after dinner we came up to start aligning the primary mirror.

The bizarre weather from yesterday was safely behind us & we settled in for a long night's observing!

The Apogee camera has to be moved around a 3x3 grid to image the entire focal plane of the telescope - shown below is one of the nine images from such a set.  The seeing wasn't ideal for much of the night, but encouraging images were obtained during intervals when the conditions improved. 

However, our excitement was tempered by significant IQ variability on a timescale of a couple of seconds which we don't yet understand.  The most likely source of this instability is the auto-collimator &/or the interferometer - two instruments mounted adjacent to the SAC on the NRS to control its attitude (tip/tilt) & focus (Z)  with respect to the primary mirror.   These pieces of equipment will undergo extensive testing over the next few days...

Bye Bye Okkie!

Although the clean room action's dried up now, there's still plenty going on next door in the spectrometer room where RSS is being put through its paces...

High hopes for getting more data tonight were dashed when the weather packed up spectacularly, much faster than any of us have ever seen!

On the up side though, this facilitated an excellent send-off for Ockert who's off to Wisconsin for a few weeks & then when he returns he'll be based at the SAAO in Cape Town.

In Sutherland, regardless of the temperature, the best conversations tend to happen while standing around outside (preferably close to a fire).

Some kinds of head-gear convey authority & have the potential to inspire respect among colleagues...  But those with huge floppy ears don't so much - we really ought to have done more to protect David & Vic from themselves!

Back in the lounge (on the Winnie The Pooh couch), 3 other bears dealt with the paparazzi in different ways.

& over on the bench - fortunately within reach of a fire extinguisher - these two worked through how to say their painful goodbyes.

All too much excitement for our brave host, who's admittedly been running a little low on beauty-sleep lately...

With friends that leave your house looking like this at 2am, who could blame Ockert for moving back to Cape Town?!